Northeast Fisheries Science Center Reference Document 05-06
Use of the Historic Area Remediation Site
by
Black Sea Bass and Summer Flounder
by Mary
C. Fabrizio,
Jeffrey P. Pessutti,
John P. Manderson,
Amy F. Drohan, and
Beth A. Phelan
NOAA National Marine Fisheries Service,
James J. Howard
Marine Sciences Laboratory,
74 Magruder Road,
Highlands NJ 07732
Print
publication date June 2005;
web version posted June 22, 2005
Citation: Fabrizio MC, Pessutti JP, Manderson JP, Drohan AF, Phelan BA. 2005. Use of the
Historic Area Remediation Site by black sea bass and summer flounder. US Dep Commer,
Northeast Fish Sci Cent Ref Doc. 05-06; 95 p.
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EXECUTIVE SUMMARY
This report presents the results of a two-year study to determine habitat
use and residency time of black sea bass and summer flounder at the Historic
Area Remediation Site (HARS) using ultrasonic tags. In 2003, fish were
implanted with individually coded ultrasonic transmitters and monitored
for one year with in situ moored acoustic receivers that covered
the HARS in a grid pattern. Prior to executing the field experiment,
we conducted laboratory trials to develop surgical and anesthesia protocols;
we also monitored the survival and growth of experimentally treated fish
for about 10 months. To elucidate habitat use observations from the field,
we conducted a behavioral experiment with black sea bass aimed at understanding
swimming speed, affinity to structure, and interactions with conspecifics.
Results of these supporting laboratory studies are also presented here.
Based on laboratory studies conducted in 2002 with fish
held in captivity at the James J. Howard Laboratory, we determined the
minimum anesthetic concentration needed to anesthetize fish prior to
surgery; we also developed surgical implantation techniques, and monitored
the long-term effects of transmitter implantation on growth and survival
of fish. Black sea bass greater than 224 mm total length (TL) required
at least 40 mg/L of clove oil to achieve full anesthetic induction in
less than 5 min and with a reasonable recovery time (less than 10 min);
summer flounder greater than 311 mm TL required 80 mg/L clove oil to
achieve similar results. Exposure of black sea bass to clove oil for
periods up to 15 min beyond the time necessary to reach full induction
was not detrimental in terms of recovery time, long-term growth, or survival.
Both black sea bass and summer flounder retained surgically implanted
transmitters for up to 10 months and had high survival rates in laboratory
trials (black sea bass survival, 100%; summer flounder survival, 92.5%).
Two of the smallest summer flounder did not survive the surgery and implantation
procedures; these mortalities reflect the difficulty in making incisions
and suturing small fish without causing critical damage to internal organs.
Black sea bass did not exhibit detrimental growth effects after 10 months;
in contrast, summer flounder exposed to clove oil and surgically implanted
with a transmitter may have been susceptible to slower growth. We attribute
this to the size of the transmitter relative to the available space in
the compressed peritoneal cavity of this flatfish.
Using anesthetic dosing and surgical techniques developed in the laboratory,
we implanted V8SC-2H transmitters (Vemco Ltd.) in 129 black sea bass
(between 220 and 431 mm TL) and 24 summer flounder (between 330 and 500
mm TL) at the HARS between May and July 2003. The only difference was
our use of Aqui-S in the field instead of clove oil as the anesthetic
agent (Aqui-S contains one of the active compounds in clove oil and is
being
developed
for use as an anesthetic in fish). The implanted transmitters emitted
a coded acoustic signal at 69 kHz every 210 s on average (the delay between
signals varied randomly between 120 and 300 s); this configuration allowed
us to achieve a 384-d battery life on each transmitter. Both black sea
bass and summer flounder had high survival rates immediately following
surgery in the field (black sea bass survival, 98.3%; summer flounder
survival, 100%).
An acoustic grid was deployed in April 2003 at the HARS to passively
record transmissions from surgically implanted fish. The grid consisted
of 72 arrays each comprised of a mooring, a receiver, and a pop-up buoy
to facilitate retrieval. Prior to implementing the grid, we conducted
a range test with a single receiver to determine the effective detection
range of the receiver. We found that detection likelihoods decreased
as distance between the receiver and transmitter exceeded 400 m. Thus,
we spaced arrays 800 m apart. In a subsequent test, we found that the
highest detection efficiency occurred when the transmitter was located
between 300 and 400 m from a receiver. By September 2004, we completed
the retrieval of arrays from the HARS and downloaded the data from receivers.
We were unable to recover 13 arrays; 5 were likely buried in disposal
material because our retrieval line broke when we attempted to bring
the array up from the seafloor; the remainder were either dragged out
of the HARS by commercial trawlers or damaged by ships' anchors. From
the recovered receivers, we downloaded a total of 1,625,315 detections
covering the period May 2003 to September 2004.
The distribution of fish at the HARS was not random; instead, fish
were patchily distributed. The number of individuals and frequency of
detections of summer flounder and black sea bass were highest in relatively
shallow, complex habitats. These habitats occurred primarily in the region
roughly corresponding to the area of capped sediments at the old mud
dump site. Based on observations with laboratory-held fish, we expect
that black sea bass were active during both day and night. Captive-held
black sea bass rarely made use of a large concrete block shelter in the
research aquarium, using the shelter for about 5.3% of the time. Thus,
we do not believe that our relatively small arrays acted as attractors
to fish at the HARS.
We estimated the probability of dispersal from the site using the Kaplan-Meier
(KM) estimator, a nonparametric approach to compute estimates of the
proportion of the sample population that remains at the study site during
a particular sampling interval. We note that all 24 surgically implanted
summer flounder were detected after release; however, one fish was not
detected in 2003, so was not considered in the dispersal analysis. Five
of the 129 transmitters from black sea bass were not detected indicating
transmitter malfunctions (3.9% malfunction rate). In addition, we detected
recordings for two transmitters at only one station from the time of
surgery and continuing throughout the winter of 2004; we interpret this
to indicate that these two black sea bass died shortly after surgery.
Consequently, for dispersal analysis, we considered only the 122 live
black sea bass with functioning transmitters.
Dispersal probabilities estimated with the KM approach indicate that
black sea bass began dispersing from the HARS on 2 June and the likelihood
of dispersal decreased about 60 d later (1 August). During this early
summer period (30 May to 23 July), 25 fish dispersed from the HARS while
we were actively implanting and releasing fish (3 others were captured
and reported by anglers). Dispersal during the early summer did not appear
to be related to temperature, salinity, or wave disturbance, as indicated
by data we retrieved from two moored CTDs and the Long Island data buoy.
Most of the fish that dispersed from the HARS at this time left the site
through the southern (48%) or western (28%) perimeters. These fish may
have been transiting toward shallower reef structures close to shore,
such as Shrewsbury Rocks. After 10 September, dispersal probabilities
increased slightly, presumably as fish moved offshore toward deeper overwintering
habitats on the continental shelf. The median dispersal date for black
sea bass was 28 October (95% confidence interval [CI]: 11 October to
5 November 2003). Between 1 and 17 November, dispersal probabilities
increased dramatically, when temperatures in shallower nearshore waters
fell consistently below those measured in deeper water on the eastern
edge of the study area. By 18 November 2003, 75% of the implanted black
sea bass had dispersed from the HARS (the 95% CI for this statistic could
not be computed). Like black sea bass, summer flounder began dispersing
from the HARS immediately after implantation; dispersal likelihoods appeared
higher than those for black sea bass. Between 2 and 20 September, summer
flounder dispersal probabilities increased significantly. The median
dispersal date for summer flounder was 5 September 2003 (95% CI: 13 August
to 12 September 2003). By 20 September 2003, 75% of the implanted summer
flounder had left the HARS (95% CI: 5 to 21 September 2003).
Male black sea bass had dispersal likelihoods that were significantly
different from those of non-males (females and fish of unknown sex).
The difference appears to arise early in the period of study such that
by 2 July, 25% of males had dispersed, whereas it was not until 8 September
that 25% of non-males left the HARS. There were no significant effects
of size on dispersal probabilities among black sea bass, but in summer
flounder, total length was significantly associated with the tendency
to disperse (smaller fish tended to spend longer time at the HARS).
In addition to these observations on dispersal, we noted the return
of one summer flounder, and one (possibly two) black sea bass to the
HARS in 2004.
INTRODUCTION
US harbors and ports are maintained for safe vessel navigation by deepening
channels and deposition of dredged materials in designated disposal sites
at sea. Since the late 1800s, dredged material from the Port of New York
and New Jersey was disposed at the New York Bight Dredged Material Disposal
Site (also known as the Mud Dump Site, MDS). Effective in 1997, the EPA
terminated use of the MDS, and designated a 15.7-square nautical mile
(nm) area about 3.5 nm off the New Jersey coast as the Historic Area
Remediation Site (HARS). The HARS currently accepts only 'uncontaminated
dredged material,' that is, material that 'will not cause significant
undesirable effects' either directly or through bioaccumulation in the
food web (US EPA 1997). The intention was to manage the site to reduce
the effects of historical disposal activities to levels conforming to
the Marine Protection, Research and Sanctuaries Act of 1972 (Public Law
92-532).
Attempts to describe significant undesirable effects require site-specific
knowledge of the ecology of fish species inhabiting the HARS. Factors
such as habitat use and residence time, as well as population characteristics
such as dispersal rates, affect the relationship between individual fish
and a specific geographic area through spatial and temporal exposures.
In this study, we investigate the habitat affinity of demersal fishes
(fish found in close association with or along the bottom) at the HARS.
Two important demersal species targeted by recreational anglers and commercial
fishers in the NY Bight are black sea bass (Centropristis striata)
and summer flounder (Paralichthys dentatus). Both species use
coastal habitats for feeding and spawning.
The black sea bass is a warm temperate fish in the
family Serranidae; the geographic range of this species extends from
Nova Scotia to southern
Florida (Bowen and Avise 1990). The group of black sea bass found off
the coast of New Jersey form part of the Middle Atlantic Bight population.
This population spends the winter offshore in the middle- to outer-continental
shelf (Musick and Mercer 1977) and migrates inshore in May as temperatures
increase. Black sea bass spawn from April through October (Able and Fahay
1998) in nearshore waters at depths between 20 and 50 m (Musick and Mercer
1977; Eklund and Targett 1990). As inshore waters increase in temperature,
some juvenile black sea bass migrate into estuaries where they spend
their first summer. Once the waters begin to cool in October-November,
young-of-the-year
and adult black sea bass migrate offshore to the warmer waters of the
continental shelf (Figure 1). Black sea bass use
complex structured areas such as rock outcroppings, reefs, and wrecks.
Their diet consists of
a variety of benthic invertebrates including crustaceans, small fish
and squid (Hood et al. 1994; Bigelow and Schroeder 2002).
Summer flounder (also locally known as fluke) are flatfishes in the
family Bothidae. The geographic range of summer flounder extends from
coastal waters of Nova Scotia to Florida (Bigelow and Schroeder 2002),
but the species is most abundant in the Mid-Atlantic Bight. In the winter,
adult summer flounder are found offshore along the continental shelf
and in the spring, summer flounder migrate inshore towards estuaries
such as Sandy Hook Bay, NJ, where they reside until fall. Summer flounder
spawn in the open ocean over the continental shelf during the fall and
winter (Bigelow and Schroeder 2002). The eggs hatch in shelf waters and
once the larvae develop into young fish in the spring, they seek shelter
and food in coastal estuaries where young summer flounder reside until
fall of their first year (Morse 1980). Summer flounder are most active
during the day foraging for food along the bottom or within the water
column (Olla et al. 1972), capturing mainly fish, cephalopods, and decapods.
Summer flounder inhabit a variety of mud and sand substrates, and may
be found
in marsh creeks, sea grass beds, and sand flats (Bigelow and Schroeder
2002).
Aquatic habitat use by fish may be studied using a variety of methods.
Standard fishery surveys gauge changes in abundance over time but do
not provide information on habitat use of individual fish. Such individualized
information can be obtained through a tagging study with acoustic "tags" (i.e.,
transmitters) that permit tracking of multiple, individual fish. Acoustic
transmitters relay information on the location of a fish either to hand-held
receivers or to passive receivers positioned in the study area; the receivers
accumulate digital data on time and place. With ultrasonic tags and a
series of moored receivers, the 'recovery' of information is virtually
100%, assuming no transmitter failure or rejection of transmitters by
fish. Such methods have been used to measure home range sizes of individual
Pacific halibut (Hippoglossus stenolepis: Hooge and Taggart
1998), tautog (Tautoga onitis: Arendt and Lucy 2000), Nassau
grouper (Epinephelus striatus: Bolden 2000), snapper (Pagrus
auratus: Parsons et al. 2003), kelp bass (Paralabrax clathratus:
Lowe et al. 2003), and blacktip sharks (Carcharhinus limbatus:
Huepel et al. 2004). Other behaviors examined include pre- and post-spawning
migrations of North Sea plaice (Pleuronectes platessa: Buckley
and Arnold 2000), and habitat use and movements of jewfish (Epinephelus
itajara; Eklund et al. 2000), tautog (Arendt et al. 2001) and juvenile
Atlantic cod (Gadus morhua; Cote et al. 2003).
Typically, ultrasonic tagging studies are expensive and thus, researchers
have employed few fish (generally not more than 30). The question of
adequate sample sizes for estimation of dispersal from a particular habitat
has not been explored. In general, investigations of population-level
questions such as survival and dispersal rates require the use of a reasonably
large number of fish. However, researchers have attempted such studies
with a wide variety of sample sizes. For instance, Cote et al. (2004)
describe the winter migration pattern of juvenile cod based on only 17
fish, and Comeau et al. (2002) report using 126 adult cod to study migration
in the open ocean. In an ongoing study, hundreds of implanted Atlantic
salmon Salmo salar smolts are being released in three Maine
rivers (Penobscot, Dennys, and Narraguagus), to track movement and survival
of fish during their downriver migration to marine environments (J. Kocik,
NOAA-NMFS, 17 Godfrey Drive, Suite 1, Orono, ME 04473, pers. comm., December
2004).
The objective of our work was to determine habitat use and residency
time of black sea bass and summer flounder at the HARS using a year-long
ultrasonic tagging experiment. This report presents the results of the
experiment conducted at the HARS in 2003-2004. Fish were implanted with
individually coded ultrasonic transmitters and monitored for one year
with in situ moored acoustic receivers that covered the HARS
in a grid pattern. Prior to executing the field experiment, we conducted
laboratory trials to develop surgical and anesthesia protocols; we also
monitored the survival and growth of experimentally treated fish for
about 10 months. To elucidate habitat use observations from the field,
we conducted a behavioral experiment with black sea bass aimed at understanding
swimming speed, affinity to structure, and interactions with conspecifics.
Results of these supporting laboratory studies are also presented here.
METHODS
Behavioral Observations of Black Sea Bass in the Laboratory
The goal of this study was to understand activity patterns and territoriality
in black sea bass, behaviors which were monitored by observing a small
group of black sea bass held in a large marine aquarium at the J. J.
Howard Marine Laboratory. Activity patterns were assessed by measuring
swimming speed, and territorial behaviors were noted by the fish's orientation
to structure and interactions with conspecifics. For this experiment,
14 adult black sea bass were collected from nearshore waters between
Shrewsbury Rocks and Point Pleasant, NJ. Four of the fish were captured
by hook and line in July 2001 and kept in laboratory tanks until 13 May
2002 when they were tagged with individually numbered internal anchor
tags. The remaining 10 fish were captured 10 June 2002 using commercial
fish traps; these fish were tagged on 25 June 2002 with internal anchor
tags after treatment with clove oil (concentrations ranged from 20 to
100 mg/L; see section on anesthetic dosing trials, below). All black
sea bass were moved to the large research aquarium on 27 June 2002, at
which time sexual identification was somewhat unreliable because the
fish were in a post-reproductive condition. Males were identifiable by
small amounts of residual milt production and a high degree of contrast
in external markings. The remaining black sea bass were either females
or smaller males. At the beginning of the observations, the mean size
of black sea bass was 286 mm total length (SD= 47.6, range=225 to 345
mm) and 366.1 g (SD=154.8, range=190-659 g). Fish were remeasured at
the end of the observations to estimate growth.
Observations were made on black sea bass behavior in a 32,000-gallon
research aquarium over a 5-month period (July to December 2002). The
research aquarium is oval-shaped (10.6 m long, 4.5 m wide, and 3 m deep),
with eight rectangular windows (0.7 m wide and 1.2 m high), one in each
end and three along each side. A recirculating system replaces 10% of
the water each week. The surface of the bottom of the aquarium is 46
m2. Photoperiod is computer-controlled and was programmed
to follow the natural daily and seasonal cycles at the laboratory location.
Water temperatures followed natural seasonal temperatures but were maintained
below 20°C to prevent thermal stress. Fish were fed chopped squid
(Loligo pealeii) once a day (weekdays) until satiation.
A structure made of concrete blocks (39.4 x 19.7 x 19.4 cm) was placed
at one end of the tank to provide a potential shelter for the black sea
bass.
We video-taped fish for a 48-hour period every other week in August
2002 and used these recordings to measure swimming speed. The camera
was directed at the tank wall on the opposite side of the tank and recordings
were made for 5 min at the beginning of each hour of the 48-h observation
period. Swimming speeds (cm/s) were determined by timing the passage
of a randomly selected fish between vertical lines (the outline of two
windows) 139.7 cm apart on the opposite tank wall. In addition, real-time
behavioral observations were made three times during the day (morning,
midday, and afternoon) for two days each week from July through December.
Three individuals were selected and observed for five minutes each to
determine the proportion of time spent resting, the number of aggressions,
and the association to the structure in the tank. Other behaviors were
noted as well.
Surgical Implantation
of Transmitters: Laboratory & Field
To ensure suitability of transmitters and implantation methods for
black sea bass and summer flounder, we conducted a series of laboratory
experiments prior to the field work at the HARS. The objective of those
studies was to determine transmitter retention rates and mortality associated
with transmitter implantation procedures. Transmitter retention rates
should be high to be useful in tracking fish over a one-year period.
Some fish, however, may encyst and eject the transmitter either through
the incision, the abdominal body wall, or via the intestines (e.g., channel
catfish Ictalurus punctatus, Summerfelt and Mosier 1984; rainbow
trout Oncorhynchus mykiss, Chisholm and Hubert 1985, Helm and
Tyus 1992; African catfish Heterobranchus longifilis, Baras
and Westerloppe 1999; and juvenile Atlantic salmon, Lacroix et al. 2004).
Retention of transmitters can be improved by ensuring proper implantation
methods and proficiency of the surgeon. Once a proper method of transmitter
implantation is developed, we expect mortality to be low.
In some species, intraperitoneal implantation of tags can lead to size-dependent
mortality (observed for Atlantic cod, S. Campana, Bedford Institute of
Oceanography, P.O. Box 1006, Dartmouth, NS, Canada B2Y4A2, pers. comm.,
August 2001). Because neither summer flounder nor black sea bass have
been previously implanted with ultrasonic tags, we also recorded size
of fish so we could examine size-dependent effects on mortality and growth.
For the surgical trials conducted in the laboratory, we used dummy
transmitters that matched the size, shape, and weight of actual transmitters
implanted in fish in 2003 at the HARS site. Selection of the transmitter
was based on size, weight, and necessary battery power life. The "rule
of thumb" for determining maximum transmitter size (in weight) is no
more than 2% of the fish's weight in air. This rule of thumb does not
appear to be supported by empirical data (Mulcahy 2003), and some researchers
reported good results with transmitters that ranged up to 8.5% of the
fish's body weight (Lacroix et al. 2004). Transmitter expulsion rates
increased significantly with increasing weight of the transmitter (Marty
and Summerfelt 1986; Lacroix et al. 2004), and larger transmitters were
associated with increases in mortality (Lacroix et al. 2004). Adams et
al. (1998) investigated effects of surgically implanted transmitters
covering a wide range of sizes (2.2 to 10.4% of fish body weight) and
found that swimming performance and vulnerability to predation of juvenile
chinook salmon Oncorhynchus tshawytscha were not affected when
the transmitter weighed no more than 5.6% of the fish's body weight.
Assuming we would implant black sea bass weighing on average 424 g and
summer flounder weighing on average 608 g, a transmitter that weighed
no more than 2% or 8.5 g would be needed for black sea bass and 12.2
g for summer flounder. (The mean weights reported here were estimated
from 89 black sea bass and 86 summer flounder that were part of the dosing,
overexposure, and surgical trials described below.) We selected the smallest
transmitter with enough battery power to last at least one year, but
weighing less than 8.5 g. The ultrasonic transmitter we selected for
field implementation (transmitter V8SC-2H, Vemco Ltd., Shad Bay, N.S.,
Canada) was 30 mm long and 9 mm in diameter, and weighed 5 g in air and
3.1 g in water. This represents 1.2% of the average black sea bass weight
and 0.8% of the average summer flounder weight.
Dummy transmitters used in the laboratory trials were constructed from
a casting mold and embedded with stainless steel nuts. Hot glue (non-hazardous
hot melt adhesive) was injected into the mold and allowed to cool before
removal. Dummy transmitters were inspected for irregularities and exposure
of stainless steel nuts; defective casts were discarded. Transmitters
were coated with a thin layer of one-hour epoxy and dipped in melted
beeswax, which provided an inert and smooth coating. We coated the transmitters
with beeswax because among fish that expel surgically implanted devices,
paraffin- and silicone-coated transmitters tended to have higher expulsion
rates than those coated with beeswax (Helm and Tyus 1992).
We elected to use clove oil to anesthetize fish prior to surgery. Use
of fish anesthetics is regulated by guidelines from the USDA Center for
Veterinary Medicine (CVM), and although clove oil is a compound that
is Generally Recognized as Safe (GRAS) when used as a direct food additive,
it is not approved for use as an anesthetic by the CVM (www.fda.gov/cvm/guidance/guide150.doc).
Regardless of this guidance, many researchers recently began experimenting
with clove oil as a fish anesthetic (e.g., Peake 1998; Taylor and Roberts
1999; Schreer et al. 2001; Woody et al. 2002); most of these studies
have been performed with freshwater or anadromous fish, and only one
study has reported the results of clove oil as an anesthetic with marine
fish species (coral reef species, Munday and Wilson 1997). To our knowledge,
no published research results exist for clove oil as an anesthetic for
temperate marine species, although some researchers are currently experimenting
with summer flounder (J. Specker, University of Rhode Island, Graduate
School of Oceanography, 218 South Ferry Rd., Narragansett, 02882, pers.
comm., July 2002). The US Fish & Wildlife Service (FWS) holds an
Investigational New Animal Drug (INAD) exemption for Aqui-S (Aqui-S New
Zealand Ltd., Lower Hutt, New Zealand), an anesthetic agent containing
50% isoeugenol (2-methoxy-4-propenylphenol), one of the active compounds
in clove oil. Aqui-S is manufactured and licensed for use in New Zealand
for the "handling and harvesting of fish and other seafood." Research
conducted under the INAD exemption will be used by the FWS to petition
the CVM for approval of Aqui-S as a fish anesthetic. With that in mind,
we initiated studies with clove oil and sought listing on the FWS INAD
exemption (# 10541); our request was granted after our laboratory trials
had begun, but in time for our surgical work at the HARS. At the HARS,
we used concentrations of Aqui-S equivalent to those used for clove oil
in the laboratory trials.
Laboratory Trials: Black Sea Bass
Collection - We collected about 125 adult black sea bass from
NJ coastal waters during May and June 2002. We deployed fish traps from
a commercial fishing vessel operating out of Manasquan, and used hook
and line techniques at Shrewsbury Rocks to capture black sea bass. Fish
captured with traps were taken from waters 70 to 80 feet deep and generally
had inflated swim bladders; some had their stomachs protruding from their
mouth (stomach evulsion). We deflated swim bladders by puncturing the
abdominal wall with a hollow needle and exerting gentle pressure on the
abdominal area (Collins et al. 1999). Fish captured by hook and line
were taken from 25- to 30-ft depths and did not exhibit decompression
trauma. Live fish were brought to the laboratory and held for later work
(anesthetic dosing, anesthetic overexposure, or surgical trials). Not
all fish survived the handling and transport process and only healthy
fish (ranging in size from 224 to 445 mm total length [TL] and 191 to
1049 g) were used in subsequent experiments.
Anesthetic Dosing Trials - Clove oil solutions were prepared
by dissolving clove oil in 95% ethanol and adding the resultant solution
to a seawater bath (66.25 l). Prior to adding the clove oil solution
to the seawater bath, we measured temperature and salinity of the water.
We exposed 3 adult fish to the following clove oil concentrations: 20,
40, 60, 80, 100, and 120 mg clove oil/L and noted the time to various
stages of anesthesia, which we modified from Summerfelt and Smith (1990).
The 5 stages we identified for black sea bass were:
| Stage |
Description |
| 1 |
weak or erratic opercular movement |
| 2 |
sporadic loss of equilibrium; difficulty maintaining position |
| 3 |
total loss of equilibrium ('belly up') |
| 4 |
loss of fin movements (loss of swimming motion) |
| 5 |
no opercular movement |
Although we initially defined 5 stages of anesthesia, we found that
transitions into the first 2 stages were gradual and determining the
time a fish needed to achieve stages 1 and 2 appeared to be somewhat
subjective. Stages 3, 4, and 5 endpoints were less subjective and were
further considered.
We conducted dosing experiments at two different temperatures (mean
temperatures: 19.7°C and 15.9°C) to examine the effect, if any, of water
temperature on induction and recovery times. However, at low temperatures,
we examined the anesthetic action and effect of only the 20, 40, 60,
and 80 mg/L doses of clove oil. Each batch of anesthetic solution was
used only once (up to 4 fish were exposed, one at a time in the bath),
and a particular fish was exposed to only one combination of clove oil
concentration and temperature.
Once the fish was anesthetized, we measured TL and weight, identified
sex, and inserted a numbered anchor tag in the dorsal musculature. Fish
were transferred to a recovery tank where we used ram ventilation to
ensure adequate water flow over the gills. Recovery occurred when the
fish regained equilibrium and swam in a forward direction (minimum of
3 fin strokes) in response to prodding in the peduncle area. We tested
the effect of clove oil concentration and temperature on mean induction
and recovery times using an ANOVA with 
=0.05.
We also examined induction times to select the minimum concentration
necessary to achieve full induction (stage 5) within 3-5 min and full
recovery in less than 10 min. Summerfelt and Smith (1990) note that an
ideal anesthetic has an induction time less than 15 min, but preferably
less than 3 min, and a short recovery time (i.e., < 5 min). Because
we could not be certain of the temperature at which we would be catching
and surgically treating fish at the HARS, we conducted the dosing trials
at two temperatures (means=15.8°C and 19.7°C) and with fish that averaged
285 mm and 352 g (n=33). We held fish an average of 291 d (9.7
months) and observed for mortalities or other abnormalities. At the end
of the observation period, we measured length, weight, and identified
sex of each fish prior to release. These observations allowed us to examine
growth of fish exposed to clove oil. During the same time period (June
2002 - July 2003) we also maintained a small group of black sea bass
(n=4 females, mean size = 270 mm, 269 g) that had not been exposed
to clove oil; estimates of growth rates from these fish were compared
with those of fish exposed to clove oil using an ANOVA with =0.05.
Anesthetic Overexposure Trials - In addition to the clove
oil dosing experiment, we conducted an overexposure test at the clove
oil concentration determined to be optimal from the dosing experiments.
Previous studies indicated that exposures greater than 5 min may unduly
prolong recovery times (Peake 1998) or even lead to death. For example,
adult sockeye salmon O. nerka survived 15 min exposures to clove
oil concentrations up to 80 mg/L, but a 15-min exposure to 110 mg/L clove
oil was lethal (Woody et al. 2002). The overexposure test provided an
indication of how much longer we could expose black sea bass without
incurring mortalities or prolonging the recovery period and aided in
establishing a maximum permissible surgery time. We exposed a group of
9 fish to the anesthetic an additional 5, 10, and 15 min after the time
necessary to achieve stage 5 anesthesia. We recorded information from
these fish similar to that from the dosing trials. We tested the null
hypothesis of no difference in recovery time among fish overexposed for
5, 10, or 15 min using an ANOVA with =0.05. The overexposure trials were
conducted at 21°C and 24.3‰ salinity with fish that averaged 301 mm TL
(mean weight, 463 g; n=9). We held fish for an average of 267
d (8.9 months) and observed for mortalities or other abnormalities. At
the end of the observation period, we measured length, weight, and identified
sex of each fish prior to release and examined growth rates.
Surgical Trials - During July and August 2002 we implanted
47 black sea bass with dummy transmitters using surgical protocols modified
for this species from methods described in Summerfelt and Smith (1990),
Wooster et al. (1993), and in several protocols acquired from other federal
laboratories (Standard Operating Procedures for Surgical Implantation,
USGS Upper Mississippi Science Center; Smolt Surgery Protocol, NOAA-Fisheries
Atlantic Salmon Program).
To perform the surgery, we exposed black sea bass to 40 mg/L clove
oil at an average temperature of 17°C and average salinity of 26.7‰ and
allowed each fish to remain in the anesthetic bath for 1 to 2 min after
achieving full induction. A few minutes of additional exposure to the
anesthetic bath were beneficial, as fish thus exposed maintained full
anesthesia during the surgical procedure. Once anesthetized, a fish was
placed dorsal side down in the V-shaped surgical cradle which was lined
with wet foam and covered with a moist chamois cloth. Anesthetic solution
(40 mg/L clove oil) was continuously circulated across the gills via
a flexible tygon tube inserted through the mouth and into the gill cavity.
Individual scales were removed from a small area on the ventral body
wall just posterior to the pectoral fins and along the midline. We found
that scale removal was necessary to permit making an incision. A dummy
transmitter, sterilized in a glutaraldehyde solution, was inserted into
the peritoneal cavity through a small incision (about 2.5 cm long) in
the ventral midline area. We used nonabsorbable monofilament nylon sutures
(Ethilon® 3-0 and 4-0 with FS-1 cutting needle, Ethicon, Somerville,
NJ) in a simple interrupted suture pattern to close the incision. The
incision was closed with three sutures and covered with a small amount
of cyanoacrylate (VetBond™, 3M, St. Paul, MN), a tissue adhesive.
Monofilament sutures are recommended for fish surgical procedures by
veterinarians
(Mulcahy 2003), and when applied in an interrupted pattern, these sutures
are associated with significantly less tissue damage (Wagner et al. 2000).
The tissue adhesive was used to bond the skin and may aid in the reduction
of wound contamination following surgery. To further reduce the likelihood
of infection, antibiotic ointment was swabbed over the sutured area.
Each fish was then weighed, its length recorded, and an individually
numbered anchor tag was inserted into the musculature below the dorsal
fin. Recovery was as described for the dosing trials. For these fish,
we also recorded induction, surgery, and recovery times.
We monitored fish until 22 July 2003 (average time of 310 d or 10.3
months; n=32) and observed for transmitter loss and mortality
associated with surgery. Prior to releasing fish, we obtained length
and weight information which we used to calculate daily growth rates
for the subset of fish that retained their anchor tag (n=32).
Growth rates for surgically treated fish were compared with those from
fish exposed to clove oil and no surgery, and with growth rates of a
small group (n=4 females) of control fish using an ANOVA with
=0.05.
Laboratory Trials: Summer Flounder
Collection - We collected about 25 summer flounder from NJ
coastal waters during May and June 2002 using hook and line techniques
from the R/V Gloria Michelle; an additional 15 fish were collected
from either Sandy Hook Bay or the Navesink River, NJ, from small boats
using hook and line. Live, healthy fish were returned to the laboratory
and held for later work (anesthetic dosing or surgical trials). In November
2002, we acquired 15 summer flounder (ranging from 313 to 509 mm TL)
from an aquaculture facility in New Hampshire (Great Bay Aquaculture,
Portsmouth, NH). These fish (subsequently referred to as the 'cultured'
fish) were transported to the J. J. Howard Marine Laboratory and allowed
to acclimate to laboratory conditions. We used active feeding as an indicator
of acclimation and postponed surgical trials until all fish were fully
acclimated. The acclimation period was long - we noted that one or two
fish began eating in late December, and by early January most of the
cultured fish were actively feeding. One cultured fish died on 20 December,
but we could not discern the cause of death (necropsy revealed no gross
organ damage, parasites, or other abnormalities). Only healthy summer
flounder (ranging from 268 to 509 mm TL) were used in subsequent experimental
trials. Ten of the 12 summer flounder from anesthetic dosing trials were
later used in surgical trials because we had difficulty capturing sufficient
numbers of fish with which to conduct the surgical trials. Also, J. Specker
(University of Rhode Island, Graduate School of Oceanography, 218 South
Ferry Rd., Narragansett, RI 02882, pers. com., July 2002) indicated that
repeated exposure of summer flounder to clove oil had no adverse effects.
Anesthetic Dosing Trials - Clove oil solutions (40, 60, 80,
and 100 mg clove oil/L) were prepared as described for black sea bass
dosing trials. We exposed 3 adult fish to clove oil and noted the time
to 5 stages of anesthesia (modified from Summerfelt and Smith 1990):
| Stage |
Description |
| 1 |
weak or erratic opercular movement |
| 2 |
sporadic loss of equilibrium; difficulty maintaining position |
| 3 |
total loss of equilibrium; inability to regain upright position |
| 4 |
mouth open |
| 5 |
no appreciable opercular movement |
Although we initially defined 5 stages of anesthesia for summer flounder,
we found that transitions into the first 2 stages were gradual and determining
the time a fish needed to achieve stages 1 and 2 appeared to be somewhat
subjective. Stages 3, 4, and 5 endpoints were less subjective and were
further considered.
Each batch of anesthetic solution was used only once (up to 3 fish
were exposed, one at a time in the bath), and a particular fish was exposed
to only one concentration. We conducted dosing experiments at 20.7°C and
27.1‰ salinity. Because we later performed surgery with both wild captured
and cultured summer flounder, we exposed 3 of the cultured fish to 80
mg/L clove oil (at 15.1°C and 22‰ salinity), measured induction and recovery
times, and compared results with those observed for wild captured fish.
Once the fish was anesthetized, we measured TL and weight, and inserted
a numbered anchor tag in the dorsal musculature. Fish were transferred
to a recovery tank where we used ram ventilation to ensure adequate water
flow over the gills. Recovery occurred when the fish swam in a forward
direction in response to prodding in the peduncle area. We examined induction
times to select the minimum concentration necessary to achieve full induction
(stage 5) within 3-5 min and full recovery in less than 10 min. We monitored
these fish from 29 July to 11 December 2002 during which time most of
the fish had become part of the surgical experiments.
Surgical Trials - In August 2002, we began surgical trials
with summer flounder. Preliminary observations indicated that fish with
incisions on the pigmented side exhibited significant hemorrhaging near
the incision site within two weeks post-surgery; we also noted incomplete
closure of the incision. Post-surgical observations of fish with the
incision on the unpigmented side indicated accelerated wound healing
and complete closure of the incision. We subsequently adopted this method
to perform surgical implantations with summer flounder.
Between August 2002 and January 2003 we implanted 53 summer flounder
with dummy transmitters using surgical protocols similar to those developed
for black sea bass. Summer flounder in the surgery trials ranged in size
from 281 mm to 508 mm TL and 202 to 1623 g (mean=389 mm TL and 685 g; n=48)
and included both wild captured (n=41) and cultured fish (n=12).
As before, we used dummy transmitters that matched the size, shape, and
weight of actual transmitters. In these surgical trials, dummy transmitters
represented 0.7% of the average summer flounder weight (685 g; n=48).
Perhaps more important than weight considerations was size of the transmitter,
as flatfish have a small peritoneal cavity and identifying an appropriately
sized transmitter was paramount (Paukert et al. 2001; Mulcahy 2003).
We also implanted 20 additional summer flounder with dummy transmitters
on 20 and 24 September 2002, but these fish died shortly after surgery
when the dissolved oxygen in the holding tanks dropped to lethal levels.
Because these fish died on 4 October 2002, little could be learned about
post-surgical survival, growth, or transmitter expulsion, so they were
omitted from further consideration.
To perform the surgery, we exposed summer flounder to 80 mg/L clove
oil at an average temperature of 17.8°C and average salinity of 24.6‰ and
allowed each fish to remain in the anesthetic bath for 1 to 2 min after
achieving full induction. As with black sea bass, a few minutes of additional
exposure to the anesthetic bath were beneficial to ensure full anesthesia
during the surgical procedure. Once anesthetized, a fish was placed pigmented
side down in a surgical cradle and anesthetic solution (80 mg/L clove
oil) was continuously circulated across the gills. Scale removal was
not necessary and an incision was made about halfway between the pectoral
and pelvic fins, but posterior to the pectoral fin insertion. The 2.5-cm
long incision was oriented from anterior to posterior (i.e., parallel
to the long axis of the body). A dummy transmitter coated in beeswax
and sterilized in a glutaraldehyde solution was inserted into the peritoneal
cavity through the incision. We used nonabsorbable monofilament nylon
sutures (Ethilon® 3-0 and 4-0 with FS-1 cutting needle, Ethicon,
Somerville, NJ) in a simple interrupted suture pattern to close the incision.
The incision was closed with three or four sutures, covered with a small
amount of cyanoacrylate (VetBond), and swabbed with antibiotic ointment.
Each fish was then weighed, it's length recorded, and an individually
numbered anchor tag was inserted between the pterygiophores of the dorsal
fin. Recovery was as described for the dosing trials. For these fish,
we also recorded induction, surgery, and recovery times.
During the post-surgical observation period, we investigated patterns
of recovery and healing in summer flounder by inspecting for signs of
infection and inflammation associated with surgical implantation. These
post-surgical observations were conducted seven times, about every two
weeks (10 September 2002, 26 November 2002, 11 and 23 December 2002,
7 and 28 January 2003, and 12 February 2003). An eighth assessment was
conducted on 25 March 2003, about one month after the last biweekly assessment,
and a final assessment was conducted on 20 November 2003. The mean assessment
time interval from date of surgery to final assessment was 383 d (or
12.6 months). All fish were assessed for a minimum of 310 d after date
of surgery. The post-surgery observation protocol consisted of capturing
fish from the holding tank with rubber nets and visually inspecting the
incision site and the overall health of the fish. The incision site observations
included: number of remaining and functioning sutures, signs of irritation
along the incision site, signs of irritation at the suture site, percent
closure of the incision, and whether the closure was tenuous or robust.
A tenuous closure occurs when the inner layer of muscle tissue closes
completely, but the outer layer and skin remain unclosed. A robust closure
was defined as 100% closure through all layers of tissue (dermal and
muscle layers). Observations on the overall health of the fish, the presence
of parasites, and the functioning level of the dermal adhesive, Vetbond,
were also noted.
In addition to evaluating the healing process, we monitored fish for
at least 310 d (mean=383 d or 12.6 months) post-surgery for transmitter
loss and mortality associated with surgery. By 20 November 2003, we terminated
the post-surgical observation period for all surviving summer flounder.
Prior to releasing fish, we obtained length and weight information which
we used to calculate daily growth rates for the subset of fish that retained
their anchor tag (n=46). Growth rates of surgically treated
fish were compared with those from a small group of control fish (n=3
cultured summer flounder) that had not been exposed to clove oil or surgery;
this comparison was performed with an ANOVA at a significance level of
=0.05. In addition, a subset of fish (n=5) was euthanized to
permit examination of internal organs and inspection for tissue damage
including adhesions, hemorrhaging, and the presence of necrotic tissue.
HARS: Black Sea Bass
We used hook and line techniques and fish traps (3 traps per string)
to capture black sea bass at the HARS from 30 May to 16 July 2003 (Table
1). The traps were allowed to soak at the site for 1-3 nights before
retrieval. Catch rates of black sea bass in the fish traps were low during
late May and early June, and many undersized (<225 mm TL and <210
g) black sea bass were captured. Undersized black sea bass and other
species were released alive at the HARS (Table 2).
As a result of changes in pressure associated with capture, black sea
bass swim bladders were inflated when the fish were brought on deck.
We followed the recommendation of Collins et al. (1999) and attempted
to deflate swim bladders using hypodermic needles and gentle abdominal
compression, but we were unable to successfully deflate swim bladders
of most fish, and the excessive handling required by this technique appeared
to further stress fish (as evidenced by notable changes in coloration).
Therefore, we retrieved the traps and 'hung' them at 30 feet for 15 min
to permit decompression of swim bladders. This decompression procedure
alleviated some of the problem, but did not completely eliminate it.
Neufeld and Spence (2004) reported similar mixed results using the same
decompression technique with burbot. Black sea bass captured using hook
and line techniques also exhibited swim bladder inflation.
We used Aqui-S to anesthetize fish in preparation for surgical implantation.
At 40 mg/L, black sea bass required more than 10 min (mean, 12.6 min; n=2)
to achieve full induction (stage 5). Although this concentration was
ideal in the laboratory, the captured fish tended to exhibit stress (dark
coloration) and were not reacting to the anesthesia in a manner consistent
with laboratory-held fish (we had difficulty achieving stage 5 anesthesia).
Previous laboratory studies indicated that black sea bass could readily
tolerate clove oil concentrations up to 120 mg/L. We therefore increased
the anesthetic concentration to 80 mg/L and this provided us with quick
induction times (mean, 3.3 min; n=127), thus minimizing additional
stress to the fish.
We implanted beeswax-coated V8SC-2H transmitters (Vemco Ltd.) in 129
black sea bass at the HARS (n=84 fish captured in traps; n=45
fish captured by hook and line) using surgical techniques identical to
those developed in the laboratory. These transmitters emitted a coded
acoustic signal at 69 kHz every 210 s on average (the delay between signals
varied randomly between 120 and 300 s); this configuration allowed us
to achieve a 384-d battery life on each transmitter. After surgery, but
while fish were anesthetized, we recorded TL, weight (using a motion-compensated
scale), and sex of the fish; we also inserted a numbered anchor tag into
the dorsal musculature. This tag was imprinted with an identification
number, a phone number to call should the fish be recaptured, and the
statement 'Not for human consumption'. Recovery of fish required ram
ventilation, and usually more than 10 min. Fish were closely monitored
during the recovery period. As soon as fish exhibited strong fin movements
(i.e., fish swam forcefully to the bottom of the holding tank), we released
the fish within the HARS site and recorded location and time of day.
Some of the fish had difficulty with swim bladder inflation (as previously
noted), but upon release, all fish were able to swim downward towards
the sea floor. Table 3 summarizes the tagging procedure (anesthesia,
surgery, and recovery) for black sea bass.
The average size of black sea bass implanted with transmitters was
307 mm TL (range, 220-431 mm; n=129) and 408 g (range, 195-995
g; n=91). Most of the fish appeared to be females (59%), but
we could not determine sex for about 13% of the fish. Surgeries were
conducted at a mean temperature of 17.8°C (range, 13.6 to 24.2°C) and 27.1‰ salinity
(range, 22.1 to 31.0‰). On average, black sea bass exposed to 80 mg/L
Aqui-S required 3.3 min (n=127) to achieve induction (range,
1.1 to 7.7 min). Recovery time was not recorded because most fish required
10 or more min to recover. Surgery time varied between 2.0 and 11.7 min
(mean, 4.1 min; n=128).
Some of the implanted black sea bass were recaptured by anglers or
commercial fishers who reported their catches (Table
4).
HARS: Summer Flounder
We captured 24 summer flounder at or near the HARS site from 17 June
to 16 July 2003 using hook and line techniques (n=23) or a bottom
trawl (n=1) (Table 1). Catch rates for summer flounder were
low. Other species captured were released alive at the HARS (Table
2).
We implanted beeswax-coated V8SC-2H transmitters (Vemco Ltd.) in 24
summer flounder larger than 280 mm TL and 215 g using surgical procedures
developed during laboratory experiments in the previous year, except
we used Aqui-S as the anesthetic agent (at 80 mg/L). After surgery, but
while fish were anesthetized, we recorded TL and weight (using a motion-compensated
scale) and inserted a numbered anchor tag into the dorsal musculature.
This tag was imprinted with an identification number, a phone number
to call should the fish be recaptured, and the statement 'Not for human
consumption.' Recovery of fish required ram ventilation, and usually
more than 10 min. Fish were closely monitored during the recovery period.
As soon as fish responded to prodding in the caudal peduncle by swimming
away, we released the fish within the HARS site and recorded location
and time of day. Table 3 summarizes the surgical
implantation procedure (anesthesia, surgery, and recovery) for summer
flounder.
The average size of summer flounder implanted with transmitters was
388 mm TL (range, 330-500 mm; n=24) and 585 g (range, 320-1080
g; n=13). Surgeries were conducted at a mean temperature of
21.7°C (range, 16.1 to 23.7°C) and 27.3‰ salinity (range, 26.5 to 30.0‰).
On average, summer flounder exposed to 80 mg/L Aqui-S required 2.3 min
(n=24) to achieve full induction (range, 1.7 to 5.3 min). Recovery
time was not recorded because most fish required 10 or more min to recover.
Surgery time varied between 2.1 and 6.8 min (mean, 4.2 min; n=24).
Some of the implanted summer flounder were recaptured by anglers or
commercial fishers who reported their catches (Table
4).
HARS Acoustic Grid Design
Array Construction and Deployment
The objective of this portion of the study was to determine the effective
detection range of receivers deployed at the HARS and to investigate
factors associated with variation in detection efficiency such as distance
to receiver and depth of the transmitter.
In October 2002, we conducted a range test in the southeastern portion
of the HARS site using a single moored receiver and a transmitter which
we deployed as a 'dummy fish.' We successfully deployed and recovered
the moored receiver (using a pop-up buoy on loan from Benthos Inc., North
Falmouth, MA). Based on the latitude-longitude position of the vessel
from which the transmitter was deployed and the latitude-longitude position
of the moored receiver, we calculated surface distances. Inspection of
the data from the single receiver indicated that transmitters were detectable
up to 600 m from the receiver, although detection frequency was significantly
diminished beyond 400 m (Figure 2). Based on this likelihood of detection,
we elected to place arrays 800 m apart in a grid pattern covering most
the HARS (Figure 3).
Each array consisted of a 400-lb pyramidal anchor, an acoustic receiver
(model VR2, Vemco Ltd., Shad Bay, Nova Scotia), a lobster float, and
a pop-up buoy (shallow water release SWR, ORE Offshore, West Wareham,
MA) fastened together with low stretch, 9,800-lb test line (Amsteel,
Samson Rope Technologies, Ferndale, WA; Figure 4). Pop-up buoy canisters
contained a 140-ft tether of braided line capable of lifting the 400-lb
mooring. Two of the arrays included a conductivity, temperature, and
depth (CTD) sensor (SBE 16, Sea-Bird Electronics, Bellevue, WA) below
the pop-up buoy, and about 3 m above the substratum. The CTDs were programmed
to continuously record temperature and salinity every 30 min.
From 14 to 25 April 2003, we deployed one array at each of 72 stations
at the HARS site (Figure 3). Arrays with CTDs were deployed in the northwest
(Station B1: 40° 24.6046' N; 73° 53.126' W) and southeast (Station H7:
40° 21.9910' N; 73° 49.7739' W) corners of HARS. The CTD at the inshore
site (Station B1) was located at a depth of 24 m, whereas the offshore
site (station H7) was 29 m deep and closer to the Hudson Canyon. The
grid of receivers covered a 13.43 nm2 area (or 4,608 hectares).
[The HARS site is 15.7 nm2.] A local notice to mariners was
filed with the U.S. Coast Guard in March 2003 to alert mariners to the
presence of our arrays. In addition, the ACOE established a 250-ft buffer
zone around each of our arrays where disposal of remediation material
was prohibited.
Array retrievals in 2003 - In August-September 2003, the acoustic
arrays were retrieved, the data were transferred from the receivers,
and arrays were re-deployed. We successfully retrieved 70 of the 72 arrays
(see Table 5) and collected data from 68 of the 70 recovered receivers.
Two recovered receivers contained no data because the battery compartment
had flooded (A7, H5). One array (B4) was not retrieved because a survey
vessel damaged the pop-up buoy after it had surfaced and before our vessel
could reach the floating canister. In an effort to retrieve the arrays
at B4, I2, and F8, three dives were conducted in late September-early
October. Divers were unsuccessful at finding the arrays at B4 and I2,
but successfully recovered the array at F8.
A number of our arrays were covered by mud, presumably from disposal
of remediation material (Table 5). The mud did not cover the receiver,
so the array functioned properly, however, retrieval of these units was
difficult and in many cases resulted in damaged instruments (3 pop-up
buoys were damaged, 1 was beyond repair; 1 receiver was damaged, although
the data could be retrieved and the unit was later repaired).
Once the arrays were retrieved, we transferred data from the receivers
to a laptop computer (model VR2PC receiver-PC interface, Vemco Ltd.,
Shad Bay, Nova Scotia) for later analysis. Overall, the 68 receivers
recovered in 2003 recorded a total of 1,333,205 detections.
Array retrievals in 2004 - During July-September 2004, we
retrieved a total of 59 arrays from the HARS. We successfully activated
36 pop-up buoys and retrieved 34 of these on the same day (buoy tether
lines broke on retrieval at two stations). Most of the remaining arrays
were retrieved several days after the initial activation of the pop-up
buoys (Table 5). We believe the buoys did not surface on the day we activated
the acoustic release because the buoy tether lines became tangled but
were eventually shaken loose after the region experienced a strong northeasterly
wind. We were unable to retrieve three of the late-surfacing buoys that
managed to float to the surface because the tether line broke during
retrieval and divers were unable to find arrays. An additional eight
arrays could not be found, bringing the total number of unrecovered arrays
to 13. We transferred data from the recovered receivers to a laptop computer
for later analysis. Because of a defective circuit board on one of the
receivers (recovered at station B1), we were able to obtain data from
only 58 receivers, and these recorded a total of 292,110 detections.
Combining the downloaded data from 2003 and 2004 produced a total of
1,625,315 detections covering the period April 2003 to September 2004.
The distribution of detections is depicted in Figure
5 for black sea
bass and summer flounder separately.
Receiver Efficiency Test
On 25 June 2004, we conducted a receiver efficiency test at the HARS
by towing a transmitter near stations A1-2, B1-2-3, C1-2-4, D2-3, E1-2-3,
F1-2-3, G1-2, H1-2, and I1-2 (Figure 6). Stations included in the efficiency
test were selected based on observed gaps in time in the transmitter
detection records from receivers moored at those stations (as indicated
in the data obtained from the data transfer activity in 2003). Stations
were also selected to represent the varying depths and levels of structural
complexity across the study area. We hypothesized that these gaps may
be associated with the presence of oceanographic features such as a thermocline,
which is known to affect acoustic transmissions in water. The V8SC-2H
transmitter (with a transmission rate of once every 10 s) used to perform
the receiver efficiency test was mounted to a tow line stabilized with
a planer; the line was also outfitted with a miniature data logger that
measured and recorded temperature and depth every 3 s (Minilog ML08-TDR,
Vemco Ltd., Shad Bay, Nova Scotia). We also deployed a CTD profiler (model
SBE 23, Sea-Bird Electronics, Inc.) at five selected sites (Figure
6).
We towed the transmitter above, through, and below the thermocline. We
examined the effect of the transmitter's depth and distance to the nearest
receiver on the efficiency of receivers by analyzing the transmissions
detected by the affected receivers.
Positions of the transmitter were derived from a GPS log file of the
vessel and additional calculations to account for depth and use of a
tow line. Latitude and longitude coordinates from the GPS file were converted
from decimal degree units to UTM (Universal Transverse Mercator) units
to permit calculations in meters. Data for the vessel's heading in the
GPS file were converted from magnetic north degrees to true north degrees,
and subsequently transformed to a unit vector angle by assuming 90 degrees
true north as the positive x axis (Figure 7A). From this angle,
unit vectors were calculated providing the direction of the offset. Any
vector may be decomposed into two vectors that are orthogonal with a
magnitude of 1; the orthogonal vectors are called unit vectors. The x- and y-component
unit vectors are represented by i and j. To obtain
the east and north correction factors for the transmitter's position
(relative to the vessel), we multiplied the negative of the i and j unit
vectors by the distance from the transmitter to the vessel (Figure
7A).
The distance from the transmitter to the vessel (in the x-y plane)
was simply the sine of the tow-line angle multiplied by the length of
tow line (Figure 7A).
Actual "through-the-water" distances from the transmitter to the receiver
were estimated using transmitter and receiver depths (Figure
7B). We
obtained transmitter depths from the data logger, which was mounted on
the tow line just above the transmitter, by transferring data from the
data logger to a PC (Minilog PC interface, Vemco Ltd.). Receiver station
depths were acquired from the fathometer aboard the vessel used to deploy
the receivers the previous year; depth of the receiver was calculated
as station depth minus 2 m (the height of the receiver off the seafloor).
The actual distance between the transmitter and the receiver was given
by the hypotenuse of the triangle having sides representing the distances
in the x-y and x-z planes (Figure
7B).
We calculated distances between the transmitter and each receiver within
1,000 m of the transmitter and binned these into 100 m increments. We
next examined the number of transmissions sent by the transmitter to
the receiver and the distance between them. Detected transmissions were
assembled from the receiver data files, which we transferred to a PC.
Percentages of transmitted signals detected by the receivers for each
100-m increment were calculated. In addition, for each 100-m bin, we
calculated the proportion of signals received from the transmitter and
reported these proportions for various 5-m (transmitter) depth bins.
We tested for significant differences in the proportion of detected transmissions
when the transmitter was within 400 m of the receivers vs. more than
400 m away using 
2 test
for the comparison of proportions from independent samples and using =0.05
(Fleiss 1981).
Habitat Characterization
In this portion of the study, we synthesized information on habitat
characteristics that were postulated to affect habitat use or dispersal.
We examined depth, sediment characteristics, and an indicator of potential
wave disturbance at the HARS using readily available data from the USGS
or NOAA data buoys.
An analysis relating the distribution of fish with physical characteristics
of the HARS requires consideration of environmental variables at the
same resolution as our fish presence/ absence data. Continuous grid coverages
of environmental variables or their indices must be averaged over zones
equivalent to the detection zones of our receivers. Receiver detection
zones are circular with a radius of about 400 m. Depth and sediment grain-size
coverages at the HARS in 2000 were provided by the USGS (Butman et al.
2002). A geographic information system (ArcGIS, ESRI, Redlands, CA) was
used to convert all coverages into UTM (Universal Transverse Mercator)
units, and to perform all necessary calculations. An index based on the
mean bottom slope was calculated to reflect changes in depth over each
100-m2 grid cell. Figure 8 displays zonal averages for depth,
sediment grain size, and mean bottom slope at the HARS.
To better understand the effect of environmental changes on fish dispersal,
we examined maximum near-bottom horizontal orbital velocities (Um)
in cms-1 as an index of potential wave disturbance and changing
weather patterns in the vicinity of the study area. Um was
calculated as:
Um = H
/Tsinh(kh)
where H is the significant wave height (m), T is dominant wave period
(s), h is bottom depth (m), and k is the wave number (Dyer 1986). The
value for k was calculated from the angular frequency, 2/T, and water
depth, h; we set h equal to 15.5 m, the depth of shallowest station at
the HARS (F5). Significant wave height and dominant wave period data
were taken from the Long Island buoy maintained by NOAA's National Data
Buoy Center (Station 44025; 40°15'01"N, 73°10'00"W; http://www.ndbc.noaa.gov/station_page.php?station=44025).
Analysis of Transmitter Data
Receiver records were organized into a relational database we constructed
for this study; such databases are useful for examining fish tagging
data (Fabrizio and Nelson 1995). We constructed 3 primary tables: (1)
Transmitter Detection (this data set contained the 1.6 million records
transferred from receivers moored at the HARS); (2) Surgery (this data
set contained information associated with the surgical implantation and
release of fish at the HARS); and (3) Array Deployment/Retrieval (this
data set summarized information associated with the deployment and retrieval
operations). Other tables were constructed to facilitate merging of information
from one table to the other (e.g., Transmitter Lookup Table, and Pop-up
Buoy Code Table).
We contacted scientists at Vemco [manufacturer of transmitters and
receivers] to assist with interpretation of false detections ('noise')
in the database. With 1.6 million records, even a very small false detection
rate of 0.1% results in 1600 false detections, or about 10 false detections
per fish. False detections were observed at the beginning or more commonly,
at the end of individual transmitter records. In some cases, we could
readily identify a detection as noise because the fish had not yet been
captured or released with a transmitter (i.e., detections for dates prior
to surgical implantation were clearly erroneous). However, in other cases,
identification of false detections was more difficult. We therefore inspected
records for each fish separately to identify and remove false detections
from the database. A single detection for a particular transmitter (i.e.,
fish) was removed if
(1) the detection could have resulted from acoustic interference
of simultaneous pulse-trains (termed 'pulse train collisions'), or
(2)
the detection occurred at a non-adjacent station and with a time lag
of more than 24 hours (in this case the noise was likely due to 'environmental'
interference.).
A pulse train refers to the sequence of coded acoustic data emitted
by each transmitter. In a few cases, we noted less than 5 detections
in a 24-h period; these were considered unreliable and removed from the
database. In many of these cases, we were able to identify acoustic interference,
but occasionally 2 to 4 detections occurred immediately after valid detections
and we could not identify a source of interference (e.g., the transmitter
was the only one detected at that station, or the station was a border
station from which a fish could swim in and out of detection limits).
To recognize that these situations may have resulted from valid transmissions,
we constructed an alternative database containing these observations
(n=1,440,651 detections) but caution that these represent a
less conservative interpretation of the acoustic data. The main database
(i.e., the conservative one) did not include these observations (n=1,440,536
detections). Excluded from both databases were the 186 detections associated
with the receiver efficiency test (previously described).
Table 6 and Table 7 present transmitter and tagging information for each
fish released at the HARS; the tables are annotated with comments that
identify transmitter malfunctions and fish that were captured by recreational
anglers or commercial fishers.
Dispersal of Fish from the HARS
We monitored the occurrence and dispersal of surgically implanted black
sea bass and summer flounder at the HARS during the course of one year
(June 2003 to July 2004). Using these data, we estimated the probability
of dispersal of fish from the site using the Kaplan-Meier (KM) estimator.
The KM estimator can be used to compute estimates of the proportion of
the sample population that remains at the study site during a particular
sampling interval (Bennetts et al. 2001). Because no assumptions are
made about the underlying hazard function, the KM approach is nonparametric.
The KM estimator is robust and easy to compute (using the LIFETEST procedure
in SAS, SAS Institute, Cary, NC); the variance of this estimator is also
well described (Pollock et al. 1989a). In addition, an extension of the
KM estimator permits analysis when new individuals are added to an ongoing
study (Pollock et al. 1989b).
Observations considered in a KM analysis may be of two types: uncensored
and censored. An uncensored observation is one for which the status (e.g.,
present at the HARS vs. absent from the HARS) is known with certainty.
Censoring occurs when the ultrasonic signal is 'lost' (due to transmitter
failure or receiver malfunction) or when the experiment is terminated.
We also followed the example in Bennetts et al. (2001) and censored observations
from fish that died prior to dispersal. Such deaths occurred when an
angler reported harvesting one of the study fish (see Table
4) or when
we determined that the transmitter signal originated from a fish that
had died. Three such occurrences were observed: two black sea bass died
on the day of surgery (one from the 18 June releases, and one from the
16 July releases); a third black sea bass died 33 d after surgery (released
23 June, died 26 July). Other censored observations required further
consideration. Consider the case of a fish present in the middle of the
HARS at time t; say this fish is captured by an angler at time t+1 but
the angler does not report the catch to us. The observation at time t from
our receiver would be considered a censored observation because at time t+1 we
did not have a record of the fish leaving the HARS (i.e., we have no
record of the fish crossing a perimeter station) and the fate of the
fish at time t+1 is unknown. With this censored observation,
we could be certain that the fish is alive and present in the interior
of the HARS at time t, but the status of the fish at time t+1 remains
unknown. (The fish may be dead or it may have slipped past a perimeter
station undetected.) It should be emphasized that with the KM approach,
the probability of not dispersing is estimated as the proportion of the
tagged fish that did not disperse out of the total number of tagged fish
(alive and status known) available to disperse during that time interval
(Bennetts et al. 2001). The properties of the hazard function (how quickly
the dispersal function changes in a given time interval) can affect uncertainty
of the estimates.
The first reported application of the KM approach to estimate dispersal
has only recently been described (Bennetts et al. 2001). In that example,
117 juvenile snail kites were fitted with radio transmitters over a 3-year
period to determine dispersal from natal areas. The sample size was large
enough to permit testing of differences in dispersal functions for birds
from two different natal habitats (lakes vs. marshes) with the log-rank
test. Results showed that juvenile birds dispersed within 220 d, with
a pulse of dispersal at around 30 d (Bennetts et al. 2001). The probability
of dispersing from lakes (stable environments) was significantly less
than the probability of dispersing from wetlands (less stable environments).
Stratification of the data allowed researchers to investigate the effect
of natal habitat type on the propensity of birds to disperse. These types
of statistical tests are critical to understanding ecological constraints
on the behavioral responses of organisms and provide more insight on
behaviors (in this case, dispersal behavior) than a simple, pooled analysis.
In our study, male and non-male black sea bass were examined for differences
in dispersal rates using the log-rank test and an approximate 2 statistic,
which we estimated using the LIFETEST procedure in SAS. We also investigated
size effects on the likelihood of dispersal using both length and weight
data. We examined the nature of the dispersal functions and followed
Collett's (2003) recommendation to use the log-rank test when dispersal
(survival) functions were roughly proportional.
Transmitter detection data for black sea bass and summer flounder were
analyzed for each fish individually. Using the first and last date each
fish was detected at the HARS, we calculated total elapsed time at the
HARS and assigned a dummy variable to indicate censoring (0=not censored,
1=censored). We considered information from recaptured fish reported
to us by anglers in determining which observations to censor. We also
censored all observations for which the last detection occurred at a
non-perimeter station at the HARS; we reasoned these fish were either
captured and not reported to us, or swam past the perimeter stations
undetected. In either case, after they were last detected, these fish
provided little information on dispersal time.
RESULTS
Behavioral Observations of Black Sea Bass in the Laboratory
The group of 14 adult black sea bass was active during both day and
night for the duration of captivity (July through December 2002). There
was no discernable activity pattern related to time of day as measured
by swimming speeds (Figure 9). We found no significant difference in
swimming speeds by month (F=1.142; df=4, 207; P=0.34);
swimming speeds pooled over months showed no significant diurnal differences
(F=3.091; df=1, 210; P=0.08). The mean swimming speed
of black sea bass held in captivity from July through December was 22.66
cm/s (N=212 observations; standard error=0.48; range, 9.1 to
65.6 cm/s).
We observed and defined a number of daytime behaviors. During resting,
fish supported themselves upright on the substrata (either the tank bottom
or a flat surface of the shelter) using the paired pelvic fins and the
anal and caudal fins. Displaying, which was limited to males, involved
extending all the fins, usually while resting on the bottom, and increasing
the contrast in the black and white markings. During a display, two males
were oriented in a parallel manner, with the head of one male opposite
the tail of the other male. The degree of contrast in body markings was
heightened in the early post-spawning period and became less noticeable
with time. Displaying appeared to be a form of conflict resolution when
the contestants competed for a resource, in this case, territory. The
display may serve as reciprocal exchange of information about relative
size and fighting ability and usually served to settle conflict without
fighting. When the contestants were two males of similar size or involved
a particularly antagonistic individual, aggression would take place.
Aggression involved pursuit of a fish (subordinate) by another fish (dominant)
and was usually observed between two males. Aggression included some
degree of chasing, ranging from simply turning and moving headfirst in
the direction of the subordinate fish, to chasing the subordinate across
the length of the aquarium. The chase sometimes ended in the dominant
fish biting a subordinate on the caudal fin, a behavior referred to as
nipping. More subtle chases resulted in the displacement, or the movement
of a subordinate fish to a new location several feet away. Subordinate
fish and other smaller fish often swam in a submissive fashion near dominant
fish with territories. Submissive swimming was marked by the use of pectoral
fins for propulsion while folding the other fins close to the body. Early
in the captivity period, aggression was high among males especially after
feeding; aggressive behaviors diminished over time (Figure
10). Conversely,
the resting behavior of males increased over time. Other fish, which
were smaller and identified as females, were not aggressive (Figure
10).
Black sea bass were observed on 18 different days from 8 AM to 4 PM
(N=1,498; 107 occasions with 14 fish per occasion) to determine
use of the concrete shelter as habitat. Fish were seen occupying the
shelter 79 times (5.3%). We defined the index of occupation as the proportion
of fish in the shelter out of the group of 14 summed over all observations
times, divided by the total number of independent observation periods.
We found no pattern over time in the index of occupation. One male was
observed to use the shelter as a territory on several occasions but different
males mostly used areas of the tank that did not contain structure.
All 14 black sea bass survived captivity and grew in TL and weight
(mean change in TL, 87.6 mm; mean change in weight, 531.8 g). On average,
black sea bass grew 0.54 mm/d and 3.3 g/d over the 161 d in captivity.
Surgical Implantation of Transmitters: Laboratory Trials
Black Sea Bass
Anesthetic Dosing Trials - We selected 40 mg/L as the minimum
dose necessary to achieve full induction in less than 5 min (mean time
to stage 5 at either temperature was 2.0 min) and with a reasonable recovery
time (at 15.9°C, mean recovery time was 3.2 min; at 19.7°C, mean recovery
time was 4.6 min).
In trials at the lower temperatures (mean=15.8°C), we found no significant
difference in the time necessary to attain stages 3, 4, or 5 among the
doses examined (20-80 mg/L), but the means tended to decrease with increasing
clove oil concentration (Table 8). Similarly, higher concentrations of
clove oil did not require significantly longer recovery periods at 15.8°C
(mean=3.8 min; n=15), but mean recovery time tended to increase
with increasing concentration (Table 8). We attribute the lack of significant
differences in induction and recovery times among concentrations of clove
oil to small sample sizes and to a narrow range of concentrations tested.
Nevertheless, clear differences in induction and recovery times were
observed at the two extremes (20 mg/L vs. 80 mg/L; Table
8).
In trials at the higher temperatures (mean=19.7°C), mean times to stages
3 and 5 varied significantly among the doses examined (20 to 120 mg/L
clove oil), such that fish exposed to higher doses required less time
to achieve either stage 3 or 5 (Table 8). We did not detect a significant
difference in mean time to stage 4 among the doses examined, but this
may be due to the variation in individual fish response (e.g., one fish
achieved stage 5 anesthesia before stage 4). Large variation in induction
time among individual fish was also reported for other species (Hoskonen
and Pirhonen 2004). At 19.7°C, the mean recovery time for black sea bass
was 364 s (6.1 min; n=18) and did not depend on clove oil concentration;
however, higher concentrations of clove oil tended to require slightly
longer recovery times (Table 8).
Comparison of the results of the dosing trials at two temperatures
indicate that at lower doses (20 and 40 mg/L), mean time to stages 4
and 5 did not differ significantly among temperatures tested (Table
9).
However, black sea bass required significantly more time to attain stages
4 or 5 anesthesia at lower temperatures (15.8°C) for clove oil doses of
60 and 80 mg/L (Table 9). These results are consistent with those observed
in salmonids and other freshwater species (Hoskonen and Pirhonen 2004;
Woolsey et al. 2004), and imply a slower uptake of clove oil at lower
temperatures. Black sea bass may require additional time to recover from
full anesthesia at higher temperatures (Table 9). In contrast, several
freshwater species exposed to clove oil had significantly reduced recovery
times at higher temperatures (Hoskonen and Pirhonen 2004; Woolsey et
al. 2004; Prince and Powell 2000). We note that black sea bass held in
captivity do not survive well at temperatures above 20°C (D. Nelson, NOAA-NMFS,
212 Rogers Ave., Milford, CT, 06460, pers. com., July 2002) and our observations
with clove oil solutions at 19.7°C may reflect a physiological response
to thermal stress as well as anesthesia.
For a given dose of clove oil, we detected no significant difference
in mean growth rates of black sea bass exposed at different temperatures
(Table 10). One of the F-tests (for the 60 mg/L comparison)
yielded a significant result for mean growth rate expressed in length,
but we believe this is spurious (Table 10). We therefore pooled our observations
among the trials conducted at two temperatures and also among doses because
we wished to test for the effect of overall exposure. Black sea bass
exposed to clove oil and observed for an average of 291 d grew an average
of 0.293 mm/d or 1.535 g/d (n=28). These rates appear to be
somewhat higher than rates estimated from four fish not exposed to clove
oil and observed for a similar period: 0.212 mm/d or 1.156 g/d. Although
no formal statistical test was performed, it appears that black sea bass
growth is unaffected by exposure to clove oil.
None of the fish in the clove oil dosing trials died as a result of
the experimental treatment; however, nine black sea bass exposed to clove
oil died on 10 April 2003 when temperatures in the seawater tanks exceeded
the lethal limit (due to seawater system problem).
Anesthetic Overexposure Trials - Exposure of fish to clove
oil for periods up to 15 min beyond the time necessary to reach stage
5 was not detrimental in terms of recovery time, long-term growth, or
survival of black sea bass.
Although mean recovery times of black sea bass exposed to an additional
5, 10, or 15 min of anesthesia tended to increase with increasing exposure,
we detected no significant difference in these means (F = 2.08; P > 0.05).
Overall mean recovery time was 5.6 min, or 1 min more than the mean recovery
time for fish that were not overexposed to 40 mg/L clove oil.
Fish overexposed to 40 mg/L clove oil grew an average of 0.224 mm/d
or 1.448 g/d (n=6). Although we overexposed 9 fish, 2 shed their
tag so although we could obtain final length and weight measurements
from those fish, we had no way of knowing which initial measures corresponded
to the final ones. In addition, one other fish died on 14 July 2002 when
it escaped from the post-exposure observation tank. Growth rates of fish
overexposed to 40 mg/L clove oil compared favorably with growth rates
of fish that were not overexposed (at the same dose), which grew 0.225
mm/d or 1.492 g/d (n=5).
Besides the single fish that escaped from the tank, no other mortalities
were observed during the 267 d post-exposure period, indicating that
overexposure to clove oil at 40 mg/L for periods up to 15 min did not
cause short- or long-term mortality.
Surgical Trials - Black sea bass larger than 224 mm TL (and
210 g) exposed to clove oil and surgically implanted with a transmitter
recovered from the procedure fairly rapidly and retained their transmitters
for long periods of time (at least 10 months). In addition, these fish
exhibited neither detrimental growth effects after 10 months, nor long-term
mortality associated with surgery or the dummy transmitters.
Black sea bass in the surgical trial averaged 313 mm TL and 468 g at
the time of surgery (range, 224-445 mm, 207-1049 g; n=47). We
implanted 27 female fish (mean size, 287 mm and 368 g) and 20 male fish
(mean size, 348 mm and 602 g). Fish exposed to 40 mg/L clove oil and
surgically implanted with a dummy transmitter required an average of
4 min to achieve stage 5 anesthesia (compared with an average of 2.4
min observed for fish in the dosing trials at 15.8 and 19.7°C) and 5.5
min to recover (compared with an average of 4.6 min observed for fish
in the 19.7°C dosing trials). Mean induction and recovery times were higher
in the surgically treated fish than observed in the dosing trials, even
though mean temperature of surgical trials (17.0°C) was intermediate relative
to the temperatures used in the dosing trials. Based on the dosing trials,
we expected induction time to be about 2.4 min and recovery to take about
4 min.
The average time to perform the surgery was 4.8 min (n=47)
but ranged from 2.7 to 9.8 min. This compares favorably with other times
reported for surgical implantation of transmitters: Prince and Powell
(2000) reported an average surgery time of 5.8 min (range, 4.0-7.4 min),
and Cooke et al. (2003) reported an average of 4.2 min for an expert
surgeon and 6.0 min for a novice surgeon performing similar surgery.
All 47 fish survived the surgery, recovered, and were actively feeding
within a few days. During the 310 d post-surgical observation period,
we found no signs of fish rejecting the transmitters.
Due to a problem with our seawater system (elevated temperature), eight
surgically implanted black sea bass from a single tank died on 10 April
2003. Necropsies on these fish confirmed the lack of transmitter rejection
or other post-surgical complications. Due to a problem associated with
an electrical storm (loss of aeration in tanks), two surgically implanted
black sea bass died on 19 July 2003. In addition to these accidental
mortalities, we observed four additional losses: one of the dead fish
exhibited 'popeye' and the remaining three died after escaping from the
holding tanks. When possible, we obtained length and weight measurements
from fish that died during the observation period.
The average growth rate of surgically implanted black sea bass was
0.220 mm/d (n=32) or 1.435 g/d (n=30). Females, which
started out smaller in length than males, tended to have higher grow
rates when measured in terms of length (mean for females, 0.248 mm/d;
mean for males, 0.184 mm/d). In contrast, males tended to gain weight
more rapidly during the course of the 310 d post-surgical observation
period (mean for males, 1.631 g/d; mean for females, 1.264 g/d). Growth
rates of surgically implanted fish were similar to those of fish exposed
to 40 mg/L clove oil (0.225 mm/d and 1.492 g/d; n=5) and similar
to growth rates of fish that were not exposed to clove oil or surgery
(mean growth rates, 0.212 mm/d and 1.156 g/d; n=4 females).
The lack of an effect of surgical implantation on growth was also observed
in a similar species, the European sea bass Dicentrarchus labrax,
though the post-surgical observation period was only 47 d (Bégout
Anras et al. 2003). Atlantic cod exhibited no significant difference
in growth among surgically implanted fish and nonimplanted fish (Cote
et al. 1999); the same was true for Colorado pikeminnow Ptychocheilus
lucius and razorback suckers Xyrauchen texanus (Tyus 1988).
Summer Flounder
Anesthetic Dosing Trials - We selected 80 mg/L as the optimal
anesthetic concentration for summer flounder from 311 to 440 mm TL (mean=366
mm) or 296 to 828 g (mean=481 g); fish achieved full induction in about
4.1 min and recovered in 5.1 min.
We found no significant difference in the time necessary to attain
stages 3 or 4 among the doses examined (40-100 mg/L), but the means tended
to decrease with increasing clove oil concentration (Table
11). Higher
concentrations of clove oil led to significantly quicker induction to
stage 5 anesthesia (Table 11). Higher doses, however, did not require
significantly longer recovery periods (Table 11). We attribute this lack
of significance to small sample sizes and a narrow range of concentrations
tested. Nevertheless, clear differences in induction and recovery times
were observed at the two extremes (40 mg/L vs. 100 mg/L; Table
11).
The response of the cultured fish to 80 mg/L clove oil was not significantly
different from that of the wild captured fish, except that cultured fish
appear to recover quicker from the anesthetic exposure (Table
12). Although
cultured fish were exposed to clove oil at a lower temperature than wild
captured fish (15.1°C vs. 20.7°C), the difference in temperature probably
did not account for the observed difference in mean recovery times among
these fish. If this were the case, we would have expected to find a significant
difference in induction time as well. Instead, we believe the difference
in observed recovery time was due to size difference of the exposed fish.
The 3 cultured fish, which ranged in size from 398 to 460 mm TL (mean=428
mm) and 770 to 1009 g (mean=855 g), were larger than the 3 wild captured
fish (TL: 311-345, mean=326 mm; weight: 296-388 g, mean=357 g) exposed
to 80 mg/L clove oil. The longer recovery time observed for the smaller,
wild captured fish may simply reflect the added time a smaller fish needs
to clear the anesthetic and regain equilibrium.
Surgical Trials - Summer flounder exposed to clove oil and
surgically implanted with a transmitter recovered from the procedure
fairly rapidly and retained their transmitters for long periods of time
(at least 10 months). In addition, these fish exhibited negligible mortality
associated with implanted dummy transmitters, but may have been susceptible
to slower growth.
We implanted 53 summer flounder in the surgical trial; these fish averaged
389 mm TL and 685 g at the time of surgery (range: 281-508 mm TL, 202-1623
g; n=48). Fish exposed to 80 mg/L clove oil at 17.9°C and surgically
implanted with a dummy transmitter required an average of 3.9 min to
achieve stage 5 anesthesia and 5.0 min to recover. This compares favorably
with observations from the dosing trials conducted at 20.7°C (mean induction
time, 4.1 min; mean recovery time, 5.0 min).
The average time to perform the surgery was 7.0 min (n=53)
but ranged from 4.1 to 13.4 min. These times are longer than the surgery
times for black sea bass and reflect the extra care necessary when working
with a laterally compressed fish. All 53 fish survived the surgery, recovered,
and were actively feeding soon after surgery (some individuals began
feeding as early as one day post-surgery). None of the fish rejected
the transmitters and we achieved a retention rate of 100% at least up
to 310 d (or 10.3 months) post-surgery.
Five fish died during the post-surgical observation period. Because
two of the fish that died were the smallest we attempted to surgically
implant (TL=281 mm, 214 g and 286 mm, 202 g), we suspect that summer
flounder exhibit size-dependent tagging mortality. These two fish died
3 and 10 d after surgery; one fish died from the accidental nicking of
the intestine by the surgeon's scalpel, and the incision of the other
fish did not fully close. One of the cultured fish that was surgically
implanted died 16 d after surgery; a necropsy revealed full closure of
the incision, no redness or swelling near the incision, no apparent damage
or swelling of internal organs, and no apparent infection. In addition,
this fish had fed the day before it died. We do not know the cause of
death. Another fish died 166 d after surgery, with no apparent inflammation
or infection, and the fifth fish died 41 d after surgery when it attempted
to escape from the holding tank. Surgical treatment of summer flounder
larger than 286 mm resulted in 3.8% mortality, but the observed mortality
may be unrelated to the surgery and presence of the transmitter. Summer
flounder smaller than 286 mm or 214 g should be avoided in surgical experiments
because delicate tissues were difficult to suture and there is increased
risk for accidental damage of internal organs during the incision or
suturing procedures.
Post-surgery observations indicate that summer flounder are able to
heal and recover quickly from surgery. Two weeks after surgery, 89.3%
of fish acquired 100% closure of the incision site (tenuous closure with
internal tissue layers completely healed, but external layers incompletely
closed; Figure 11). After 4 weeks, 69.8% of fish acquired robust closure
of the incision site, and by 12 weeks post-surgery all fish exhibited
and maintained robust closure of the incision site (Figure
11). The level
of skin irritation at the incision and suture puncture sites varied during
holding time and may be a function of handling effects, type of substrate
in the tank (coarse sand), and the number of animals in the holding tank.
In general, incision site irritation decreased rapidly among fish but
was present up to 1 year after surgery in 30% of the summer flounder
(Figure 11). Between 60 and 80% of fish exhibited irritation at the suture
site during the first 12 weeks post-surgery; about 60% of summer flounder
exhibited suture site irritation up to 1 year after surgery (Figure
11).
Necropsies on five fish revealed that the level of irritation did not
compromise tissue closure or penetrate beneath the dermal tissues. We
found no signs of adhesions, hemorrhaging, necrotic tissue or any other
damage; dummy transmitters were free and intact. Summer flounder tolerated
the implantation of dummy transmitters, although they exhibited irritation
of the skin at the incision and suture sites. Overall, we found no deleterious
effects of surgery (as determined by gross morphological inspection).
Mean initial size of surgically treated fish that survived at least
310 d and retained their tag (n=43) was 394 mm TL (range: 285
- 508 mm) and 707 g (range: 266 - 1623 g); mean initial size of control
fish was 470 mm TL (range: 420 - 509 mm TL) and 1019 g (range: 701 -
1317 g). The mean growth rate of surgically implanted summer flounder
was 0.075 mm/d or 0.524 g/d (n=43). Growth rates of surgically
implanted fish were lower than those of control fish that were not exposed
to clove oil or surgery (mean growth rate, 0.114 mm/d and 2.359 g/d; n=3).
Six of the surgically implanted fish had negative growth rates. Slower
growth rates may have resulted from reduced feeding of the transmitter-implanted
fish, although we have no estimates of consumption for the two groups
of fish because all summer flounder were fed ad libitum. It
should be noted that in all other respects, the control fish were handled
similarly during the post-surgical assessments so handling stress was
equal among surgery and control fish.
HARS Acoustic Grid
We formulated a series of hypotheses about the arrays that we were
unable to recover from the HARS in 2004:
The arrays were dragged out of the HARS site by commercial trawling
in the area. We believe this was a major contributor to our inability
to retrieve arrays. During early 2004, a broken pop-up buoy was returned
to us by a commercial fisher who operated a trawler in local waters.
In addition, the G7 array was recovered west of the location at which
it had been deployed, implying the array was dragged away from its
deployment site.
The pop-up buoys (and arrays) were damaged or fouled by ships'
anchors. The damage may entail breaking of the hydrophone on the
pop-up buoy such that the acoustic release signal cannot be received
(and therefore the buoy is not activated to pop), or entanglement of
the array such that the pop-up buoy cannot break free to float to the
surface. Many party boats from Atlantic Highlands and Point Pleasant,
NJ routinely anchor in the area. Some of our arrays sustained damage
(e.g., the stainless steel strongbacks on 10 of the receivers recovered
in 2004 were bent and one receiver had a broken hydrophone), indicating
possible fouling with trawl warps or anchor rodes.
The moorings or pop-up buoys were covered in disposal material.
Although a 250-ft buffer zone had been established around our deployment
locations in which no material placement was permitted, in at least one
case, the buffer zone appears to have been violated (station C2; see
Figure 12). Disposal activities from April 2003 to July 2004 were somewhat
associated with our failure to recover some of the arrays. In addition,
we noted that arrays retrieved from stations B2, B3, B7, C1, C2, and
I1 had a thick layer of mud or clay covering the mooring (Table
5). Arrays
at stations C5, D5, D6, E6, and H4 were not recovered because the buoy
tether lines broke when we attempted to lift the moorings off the seafloor;
we suspect that some (perhaps all) of these stations received dispersal
material that may have buried the moorings.
Receiver Efficiency Test
The highest receiver efficiency was observed when
the transmitter was located between 300 and 400 m from a receiver (25.3%
detection rate;
Figure 13). We identified a significant (2 =
470.6, df=1, P<0.05)
difference in receiver efficiency when transmissions were sent within
400 m (19.7% detection rate) of a receiver relative to those sent from
400 m or more (1.3% detection rate; Figure 13).
Receiver efficiency varied with transmitter depth, but tended to be
highest when the transmitter was below the thermocline or within 5 m
of the surface (Table 13). For example, at a distance of 300 to 400 m,
the highest receiver efficiency occurred when the transmitter was within
5 m of the surface (89.5% detection rate). We suspect this high efficiency
may be associated with sound waves reflecting off the sea surface. Another
possibility is that the directional tilt of the transmitter (transmissions
are emitted from one end of the transmitter) may have facilitated a direct
signal to the receiver. The tilt of the transmitter at deeper depths
may not have been optimal and may have led to lower detection efficiency
for transmissions emitted in deeper waters. Receiver efficiency was lowest
when the transmitter was in the thermocline (see efficiency data for
10-15 m depth interval, Table 13). Temperature profiles taken along the
test track indicated the presence of a thermocline between 12 and 15
m (Figure 14). Receivers consistently detected transmissions when the
transmitter was located between 15 and 25 m (i.e., below the thermocline).
Because both black sea bass and summer flounder are demersal, transmissions
from individual fish are likely to be sent from depths below the thermocline,
and we achieved better receiver efficiencies in these circumstances.
The angle at which the transmitter was attached to the towing line
as well as the speed of the transmitter through the water may have negatively
biased our estimates of detection efficiency (i.e., the receivers may
achieve higher efficiencies than those reported here). Although detection
rates appear low (on the order of 3% or less), we caution that the transmitter
was moving through the water at a faster rate than expected for fish.
We expect detection rates for transmitters implanted in fish to exceed
those reported here. In addition, the results of the efficiency test
support the receiver placement used at the HARS because we achieved good
detection results when the transmitter was no more than 400 m away from
the receiver.
Habitat Characterization
Bottom water temperatures in the study area increased from 10°C on
30 May 2003 (date of first release) to values periodically exceeding
20°C at both inshore and offshore CTD sites from 18 to 22 September 2003
(Figure 15). Temperatures decreased in the fall but remained above 7°C
until early January. Black sea bass are reported to migrate to offshore
areas when bottom water temperatures approach 7°C (Musick and Mercer
1977). Water at the inshore site was generally warmer (
= +2°C, max=
+7°C) than at the offshore site from May through October 2003. However,
this relation changed between November 2003 and mid-April 2004 when temperatures
were consistently higher at the offshore site. The lowest temperatures
were recorded during February and March 2004 (minimum= 3°C). Shelf water
warmed in the spring and was consistently higher than 7°C at the inshore
site after mid-May 2004.
Conductivity sensors on both CTDs lost calibration in early December
2003. As a result, bottom water salinity data are available only for
2003. Salinity in the study area averaged 31.3‰ and increased over the
season. Salinities were about 0.3‰ below average from June through mid-August
and 0.3‰ higher than average through November 2003 (Figure
15). Bottom
water was about 0.5‰ lower at the inshore site than the offshore site
(max=3.9‰; min= -7.2‰). However, from 13 to 18 September 2003, relatively
low salinities were observed at the offshore site. During this period,
Hurricane Isabel moved through the study area as indicated by the presence
of high long-period waves at the Long Island Buoy.
Potential wave disturbance of bottom habitats in the HARS was relatively
low from June through August and then increased during the fall of 2003
(Figure 16). Maximum near-bottom horizontal orbital velocities calculated
for the shallowest station averaged 0.2 cms-1 (SD=1.3; range,
0 - 0.61) during the summer months. The potential for wave disturbance
was high during September (mean near-bottom horizontal orbital velocity,
Um = 0.44, SD = 0.26) particularly from September 18 to 19
when high long-period waves generated by Hurricane Isabel moved through
the study area. Near-bottom horizontal orbital velocities as high as
1.72 cms-1 were calculated for this period. The potential
for high wave disturbance was also evident in the study area from October
through December (mean Um=0.32, SD=0.28, max=1.72), but these
conditions were not sustained for long periods of time.
Seafloor characteristics at the HARS vary and include areas of both
relatively homogeneous and highly variable bottom characteristics (Figure
8). An example of the heterogeneity of the site is depicted in Figure
8C where similar relatively flat bottom habitat is found at stations
in the southern portion of the study area; in contrast, the bottom slope
in the remainder of the HARS is more variable from station to station.
The portion of the study area with the greatest change in bottom slope
occurs within a 'box' formed by stations D1 to D4 and G1 to G4. This
box is characterized by contiguous stations with large changes in depth
(both positive and negative) adjacent to stations with relatively small
changes in depth. This area includes stations that are relatively deep
adjacent to the most shallow stations in the study area. Large changes
in depth also characterize the eastern edge of the study area, where
depth changes are continual and unidirectional.
The southern portion of the HARS is characterized primarily by medium-grain,
muddy sands; the northern and central areas have primarily fine-grain
muddy sediments. However, variations in sediment grain size composition
exist within these areas. The 'box' formed by stations D1 to D4 and G1
to G4 is characterized by large variations in sediment grain size; within
the box, an area of relatively coarse sediments is surrounded by stations
with fine, muddy sediments.
Dispersal of Fish from the HARS
We examined the transmitter data collected by receivers at the HARS
for evidence of transmitter malfunction and fish mortality. All 24 surgically
implanted summer flounder were detected after release; however, one fish
was not detected in 2003, so was not included in the dispersal analysis
(Table 7). Receivers at the HARS did not detect 5 of the 129 transmitters
(3.9% malfunction rate) from black sea bass indicating that implanted
transmitters malfunctioned shortly after implantation or release (Table
6). Transmitter malfunction rates of 2-3% are typical and failure rates
of 5% are not uncommon (T. Sheehan, NOAA-NMFS, 166 Water St., Woods Hole,
MA 02543, pers. comm., April 2002). In addition, we detected recordings
for two transmitters at only one station from the time of surgery and
continuing throughout the winter of 2004; we interpret this to indicate
that the fish had died shortly after surgery. Consequently, for dispersal
analysis, we considered only the 122 live black sea bass with functioning
transmitters.
Because the implantation period for black sea bass and summer flounder
extended over several weeks (black sea bass: 30 May to 16 July; summer
flounder: 17 June to 16 July), and because anglers were actively fishing
at the HARS during our implantation period, we could not make the following
necessary assumptions: (1) that implantation occurred over a short period
of time (relative to the time period of interest) and (2) that no fish
were removed from the HARS (e.g., through angler harvests) prior to the
completion of all surgical implantation. Therefore, we adjusted the elapsed
time for each fish to permit estimation of total time spent at the HARS.
We assumed that all black sea bass were present at the HARS by 2 June
2003 and calculated the adjusted elapsed time relative to this date.
For example, if a fish was surgically implanted on 7 June 2003, and it
dispersed from the HARS 25 d later, then it's adjusted elapsed time would
be 30 d (25 + 5). Similarly, for summer flounder we assumed all fish
were present at the HARS by 24 June 2003. These dates were selected to
minimize the number of fish for which negative adjustments were made
(e.g., if a black sea bass was surgically implanted on 30 May 2003, we
would subtract 3 d from it's elapsed time). In addition to the adjustments,
we note that 53.3% of black sea bass observations were censored and 4.4%
of summer flounder observations were censored. Many of the censored black
sea bass observations were due to last detections that occurred within
the HARS but not at a perimeter station; whether these fish were captured
(and therefore removed from the study site) or the transmitter ceased
to function, the fate of these fish remains unknown. As such, censored
fish contribute no further information on occurrence at the site after
the time of their last detection.
Dispersal probabilities estimated with the KM approach and using the
adjusted data indicate that black sea bass began dispersing from the
HARS on 2 June and the likelihood of dispersal decreased about 60 d later
(1 August) (Table 14). In the early portion of the study period (30 May
to 23 July), 25 fish dispersed from the HARS while we were actively implanting
and releasing fish (3 others were captured and reported by anglers).
Most of the fish that dispersed from the HARS at this time left the site
through the southern (48%) or western (28%) perimeters. After 10 September
(100 d after 2 June), dispersal probabilities increased slightly (Figure
17A). The median dispersal date for black sea bass was 28 October (95%
confidence interval: 11 October to 5 November 2003). Between 1 and 17
November, dispersal probabilities increased dramatically, and by 18 November
2003, 75% of the implanted black sea bass had dispersed from the HARS.
Unfortunately, the confidence interval (CI) around this date is inestimable
because the largest observation was censored, and when this occurs, the
dispersal function is undefined beyond that time period (Collett 2003).
Like black sea bass, summer flounder began dispersing from the HARS immediately
after implantation (Table 15); dispersal likelihoods appeared higher
than those for black sea bass (Figure 17B). Between 2 and 20 September,
summer flounder dispersal probabilities increased significantly (95%
CI for 2 September: pdispersal = 0.2739 - 0.6959;
95% CI for 20 September: pdispersal = 0.7097 - 1.0).
The median dispersal date for summer flounder was 5 September 2003 (95%
CI: 13 August to 12 September 2003). By 20 September 2003, 75% of the
implanted summer flounder had left the HARS (95% CI: 5 to 21 September
2003).
We also examined the KM estimates of dispersal probabilities using
the less conservative data set for black sea bass and summer flounder
detections. (Recall that the less conservative data set included detections
omitted from the conservative data set as described in the Methods section,
HARS Acoustic Grid Design, Analysis of Transmitter Data.) We found little
difference in the probabilities of dispersal between the conservative
and less conservative data (Figure 18). The median dispersal date was
3 November 2003 (95% CI: 12 October to 5 November) for black sea bass,
and 3 September 2003 (95% CI: 13 August to 11 September) for summer flounder.
As before, 75% of the black sea bass dispersed from the HARS by 18 November
2003 (95% CI: 5 November to 6 December 2003), and 75% of the summer flounder
dispersed by 20 September 2003 (95% CI: 5 to 21 September 2003).
Because the conservative and less conservative data sets provided similar
estimates for these two species, we worked with the conservative data
set to further investigate factors associated with dispersal likelihoods.
Results of the log-rank test for sex and size effects on black sea bass
dispersal probabilities indicated that male fish dispersal likelihoods
were significantly different from those of non-males (females and fish
of unknown sex; 2 =
4.838, P=0.03). The difference
appears to arise early in the period of study such that by 2 July, 25%
of males had dispersed, whereas it was not until 8 September that 25%
of non-males dispersed from the HARS. There were no significant effects
of size (measured as TL or weight) on dispersal probabilities among black
sea bass (2TL =
0.051, P=0.82; 2weight =
0.304, P=0.58).
Results of the log-rank test for size effects on summer flounder dispersal
probabilities indicated that fish size (TL) was significantly associated
with tendency to disperse (2 = 3.465, P=0.06) and
fish weight was somewhat less so (2 = 3.056, P=0.08).
Because we had few summer flounder in this study, we did not calculate
a size-based dispersal likelihood. We note, however, that smaller fish
tended to spend longer time at the HARS than larger fish of this species.
In addition to these observations on dispersal, we noted the return
of one summer flounder, and one, possibly two, black sea bass to the
HARS in 2004. The summer flounder (transmitter # 98) had not been detected
at the HARS in 2003, but did return on 29 May 2004; this fish stayed
at the HARS until 7 June 2004, when it was no longer detected (the lack
of detection for this fish after 7 June 2004 may be due to the end of
the battery life of the transmitter). One black sea bass (transmitter
# 48), which left the HARS on 17 November 2003, returned on 13 May 2004
and was present for only one day. Our receivers also recorded six detections
at H5 for an additional black sea bass (transmitter # 167) between 10
May and 21 June 2004; this fish may have returned to the HARS, but because
we had so few detections (and not more than 1 per day), we can not be
certain these are 'true' detections. However, we note that this period
possibly represents the last days of the battery life and inconsistent
transmissions may occur during that time. These observations of fish
returning to the HARS represents a relatively high return rate for summer
flounder, and possibly also for black sea bass, given that both species
are exploited year-round, in nearshore waters from the spring to the
fall, or offshore in the winter otter trawl fishery (Shepherd and Terceiro
1994).
DISCUSSION
Survival of Surgically Implanted Fish - Both black sea bass
and summer flounder retained surgically implanted transmitters and had
high survival rates in laboratory trials (black sea bass survival, 100%;
summer flounder survival, 92.5%) and in the field (black sea bass survival,
98.3%; summer flounder survival, 100%). The mortality observed with laboratory
summer flounder was most likely size-dependent and may have reflected
the difficulty of novice surgeons working with small fish (Cooke et al
2003). We attribute the high retention rate of transmitters in the surgical
trials with black sea bass and summer flounder to the use of appropriately
sized transmitters coated in beeswax. For summer flounder, the size of
the transmitter (rather than the weight) may have been a factor contributing
to the slower growth rates observed for laboratory-held fish. The cylindrical
transmitter was accommodated in a flattened peritoneal cavity and may
have prevented the fish from ingesting sufficient food, thus leading
to poorer growth. No long-term growth effects were observed for black
sea bass. Overall, by carefully monitoring size and performing surgery
on fish capable of surviving the procedure, we achieved excellent results
from the implantation of ultrasonic transmitters in these species at
the HARS.
Effect of Arrays on Aggregation of Fish - We note that the
72 arrays at the HARS may be construed as placement of new structure
which could serve to aggregate black sea bass at the HARS, thus possibly
compromising information on habitat use. However, arrays represented
an insignificant volume compared with the available volume at the HARS.
The 72 arrays (pop-up buoy, receiver, float, line, and mooring) comprised
4.73 m3. Assuming that black sea bass use the bottom 2 meters
of water and that the HARS is 15.7 nm2 (1 nm=1,852 m), the
space potentially occupied by black sea bass is 107.7 million m3;
the arrays represent an insignificantly small proportion of the potential
habitable space.
Association of Fish with Bottom Substrates - Although black
sea bass were detected at every HARS station from which we recovered
a receiver, and summer flounder were detected at 60 of the HARS stations,
the distribution of fish at the HARS was not random. Instead, fish were
patchily distributed. The number of individuals and frequency of detections
for summer flounder and black sea bass were highest in relatively shallow,
complex habitats. These habitats occurred primarily in the region defined
by north-south transects C-G and east-west transects 1-5. This roughly
corresponds to the area of capped sediments at the old Mud Dump Site.
Topographic complexity and substrate heterogeneity appeared to be high
in this region as variation in bottom slope and sidescan sonar reflectance
were also relatively high (Figure 19). Variable slope and sonar reflectance
values indicate that the region may comprise a mosaic of hard structures
embedded within a matrix of softer substrates. Seventy-three percent
of black sea bass detections (detections from 116 individuals), and 89%
of summer flounder detections (detections from 19 individuals) were recorded
in this area, which accounted for 35% of total surface area of the HARS.
Fish were also detected (although less frequently) in the southwestern
region of the study area (north-south transects A-C, and east-west transects
6-8), where relatively large changes in bottom slope were associated
with large sand waves visible in sidescan sonar imagery (Figure
19).
These sand waves are also conspicuous features further south and west
of the HARS. Three percent of black sea bass detections (detections from
18 individuals) and 9.4 % of summer flounder detections (detections from
12 individuals) were recorded in this area.
Patterns of habitat association observed in our study are consistent
with those reported elsewhere for these species. Black sea bass use hard
structures for resting and refuge but feed on benthic invertebrates on
adjacent soft substrates (Steimle and Figley 1996). This species has
also been reported as relatively abundant in sand wave habitats (Wigley
and Theroux 1981). In estuaries, summer flounder are most often associated
with soft substrates adjacent to structurally complex habitats such as
eelgrass beds and oyster reefs that are rich in food resources (Able
and Kaiser 1994; Packer and Hoff 1999).
Dispersal Analysis and Censored Observations - Acoustic 'gates'
are often used to passively monitor the passage of fish from an area
of interest to an adjacent area (e.g., Egli and Babcock 2004; Comeau
et al. 2002). However, we found that such 'gates' or 'perimeters' are
not always fully reliable. Not all of the black sea bass implanted with
a transmitter dispersed through a perimeter station at the HARS. Some
of the fish were captured by anglers (and reported to us), and others
were last detected in the interior of the HARS. We considered the hypothesis
that these fish may have dispersed from the HARS by swimming past the
outer perimeter of the acoustic grid without detection. Using observations
on the swimming speed of black sea bass, we investigated this possibility.
Non-detection at a perimeter station occurs if the fish is able to swim
past the station during an interval of time in which the transmitter
is silent (i.e., 3 to 5 min). If a black sea bass is 800 m away from
a perimeter station at the HARS, say at D2, and if the fish swam in a
straight-line path at the average speed observed in the research aquarium
(22.66 cm/s), then it would require about 58.8 min to reach D1, a perimeter
station 800 m away. If the fish were swimming at the maximum speed (65.6
cm/s), then it would require about 20.3 min to reach D1. During that
time, the transmitter in the fish swimming at the mean speed would have
transmitted about 15 signals, and the one in the fish swimming at the
maximum speed would have transmitted about 5 signals. Thus, even fast
swimming fish should be detected as they swim past a perimeter station.
Fast moving black sea bass were observed at the HARS; for instance, on
21 August 2003, one fish (transmitter # 33) was detected at 10:37 a.m.
at station G6 and at 10:59 a.m. at station H6. We note, however, that
sound detection is complex and some transmissions from fast-swimming
fish may have gone undetected at perimeter stations. As we demonstrated
at the HARS, the likelihood of detection is clearly affected by the distance
between the transmitter and the receiver, the position of the transmitter
relative to the thermocline, and by interactions from environmental 'noise'.
We believe the most likely explanation for some of the censored data
is capture by anglers; during the summer and fall, fishing pressure for
black sea bass at the HARS is intense and 89.2% of our censored observations
occurred at 12 stations that were in the area most heavily fished (stations
D3-4, E3-4-5, F4-5-6, and G3-4-5-6); 21.5% of censored observations were
at station F5, which is adjacent to the yellow "NY" buoy also known as
the Mud Buoy. [The Mud Buoy is located at 40° 22' 49"N 73° 50' 42"W and
is 370 m from F5, 550 m from F6, 605 m from G5, and 725 m from G6.] The
12 black sea bass recaptured by anglers or commercial fishers and reported
to us represent 9.8% of the total number of live, implanted black sea
bass released at the HARS. This compares favorably with the 13.1% recapture
rate reported for black sea bass tagged and released off Long Island
and northern New Jersey in 2002-2003 (Consensus Assessment Report 2004).
Assuming the reporting rate for black sea bass along the Atlantic coast
(north of Cape Hatteras) is 63.6% (Consensus Assessment Report 2004),
then we would expect that about 19 fish were captured. This number is
much lower than the number of fish that were censored because they were
last detected at an interior station at the HARS but not reported as
being captured (n=61). Either the exploitation rates at the
HARS are significantly higher than the overall rates estimated from Massachusetts
to North Carolina, or reporting rates for fish captured near the HARS
are significantly lower (around 18-20%) than the overall rate reported
in the Consensus Assessment Report (2004). Without additional tagging
studies, we can not be certain which factor (exploitation, reporting
rate, or both) contributed to the discrepancy.
Dispersal of Fish from the HARS - Black sea bass dispersal
from the HARS appeared to be highest in the early summer and late fall
(Figure 17A). A relatively large number of fish (N=19) dispersed
from 13 June to 2 July 2003. Dispersal during this period did not appear
to be related to temperature, salinity, or wave disturbance (Figure
20).
Many of the fish dispersing during this early summer period moved through
the western perimeter of the study area. These fish may have been transiting
toward shallower reef structures close to shore, such as Shrewsbury Rocks.
The dispersal rate of black sea bass from July through mid-October was
relatively low (~ 4.5 fish per month). Dispersal increased during late
October and November, presumably as fish moved offshore toward deeper
overwintering habitats on the continental shelf (Musick and Mercer 1977).
A large number of fish (N=7) dispersed from the study area in
mid-November when temperatures in shallower nearshore waters fell consistently
below those measured in deeper water on the eastern edge of the study
area (Figure 20). The last black sea bass was detected in the study area
on 14 December when temperatures averaged about 9°C; it resided at the
HARS for 175 d (unadjusted). Black sea bass are reported to migrate offshore
to overwintering habitats when bottom water temperatures approach 7°C
in the fall (Colvocoresses and Musick 1984; Shepherd and Terceiro 1994).
Summer flounder dispersal from the HARS was relatively constant throughout
the summer and fall of 2003 (~3.3 fish per month; Figure
20). A relatively
large number of fish (N=8) moved out of the study area on 20
September when near-bottom orbital velocities and temperatures were elevated
as a result of the passage of Hurricane Isabel. The last summer flounder
dispersed from the study area on 18 November, when temperatures averaged
about 13-14°C; it resided at the HARS for 148 d (unadjusted). Summer flounder
are reported to migrate offshore to overwintering and spawning areas
where temperatures exceed 8°C (Sissenwine et al. 1979).
Our acoustic tagging results with black sea bass and summer flounder
clearly show that both species use the HARS; some individual fish are
present at the HARS for short periods (less than 1 month), whereas other
individuals may reside at the HARS for a significant period of time.
Summer flounder were present up to 155 d and black sea bass were present
up to 199 d, but the actual residency time of a particular fish is highly
variable.
ACKNOWLEDGMENTS
This work was funded by the U.S. Army Corps of Engineers; we thank Todd
Bridges (USACE, Engineer Research and Development Center, Vicksburg,
MS), Monte Greges (USACE, New York District, New York City), and Stephen
Knowles (USACE, New York District, New York City) for their support and
encouragement throughout
the study.
We also thank Andrew Draxler (NOAA-NMFS, Highlands, NJ) for introducing
us to the ecological issues at the HARS and Allen Bejda (retired, NOAA-NMFS)
for early discussions that helped us formulate this study. Richard Lathrop
(Center for Remote Sensing and Spatial Analysis, Rutgers University,
New Brunswick, NJ) provided data and seafloor habitat maps for the New
York Bight. We are grateful to Commander Emily Christman, Shep Smith,
Marc Moser (NOAA Marine Operations Center), and crew of the NOAA vessel Thomas
Jefferson for providing ship time and high resolution side-scan
sonar imagery of the HARS to assist us with array retrievals in 2004.
Discussions with Jim Nichols (USGS-Patuxent Wildlife Research Center,
Laurel, MD) and Ken Pollock (NC State University, Raleigh, NC) led to
our use of the Kaplan-Meier estimator for dispersal analysis. We thank
John Kocik (NOAA-NMFS, Orono, ME), Tim Shaheen (NOAA-NMFS, Woods Hole,
MA), and the smolt tagging team in Orono for teaching us surgical techniques
used with Atlantic salmon, and Bridget Dunnigan, D.V.M., and Roger Williams,
D.V.M. (NOAA-NMFS, Woods Hole, MA) for guidance on general surgical procedures
for fish. Raquel Cunha kindly provided her photographic expertise and
documented the black sea bass surgery trials. Linda Stehlik designed
the notice instructing fishers about reporting information from recaptured
fish. We thank Dale Webber (Vemco Ltd., Shad Bay, Nova Scotia) for guidance
on selection and use of acoustic transmitters and receivers appropriate
for our study. In addition, many individuals - NOAA employees, contractors,
students, and volunteers - assisted with every aspect of the investigation.
We gratefully acknowledge their contribution:
Anesthetic trials and surgical implantation:
John Rosendale (technician,
NOAA-Fisheries)
Frank Morello (laborer,
NOAA-Fisheries)
Adam Pollack (intern, Long Island University)
Naeem Willett (intern, University
of Maryland-Eastern Shore)
Patricia Shaheen (volunteer)
Collection and maintenance of summer flounder and black sea bass:
John
Rosendale (technician, NOAA-NMFS)
Fred Scharf (NRC post-doctoral
fellow, NOAA-NMFS)
John Hilbert (contractor, NOAA-NMFS)
Adam Pollack (intern, Long Island University)
Corrin Flora (intern, Long
Island University)
Tait Olson (intern, Long Island University)
Josh Siegell (intern, Long Island
University)
David Wang (intern, Long Island University)
Joseph Lorino (intern, Long
Island University)
Joseph Rommel (volunteer)
Behavioral observations of black sea bass:
Julie Cummings (volunteer,
Brookdale Community College)
Adam Pollack (intern, Long Island University)
Corrin Flora (intern, Long
Island University)
Construction of arrays:
John Rosendale (technician, NOAA-NMFS)
John Hilbert (contractor, NOAA-NMFS)
Frank Morello (laborer, NOAA-NMFS)
Julie Cummings (volunteer, Brookdale
Community College)
Jonathan Smythe (volunteer, Brookdale Community College)
CTDs and data recovery instructions:
David Mountain (Chief, Oceanography
Branch, NOAA-NMFS)
Maureen Taylor (oceanographer, NOAA-NMFS)
Retrieval and re-deployment of acoustic arrays, 2003:
Patricia Shaheen
(volunteer)
John Rosendale (technician, NOAA-NMFS)
John Hilbert (contractor, NOAA-NMFS)
Retrievals, July 2004:
Adam Pollack (intern, Long Island University)
John Sibunka (fishery biologist,
NOAA-NMFS)
Don Shrump (contractor, NOAA-NMFS)
Tagging of fish at HARS site:
John Hilbert (contractor, NOAA-NMFS)
Patricia Shaheen (volunteer)
Andrew Baum (fisheries aide, NOAA-NMFS)
Adam Pollack (intern, Long Island
University)
John Rosendale (technician, NOAA-NMFS)
Holly Jantz (intern, Rutgers University)
Brian Governale (volunteer)
Meryl Segal (intern, Long Island University)
Zoey Chenitz (volunteer)
Elden Hawkes (intern, University of Maryland-Eastern
Shore)
Jennifer Samson (NRC post-doctoral fellow, NOAA-NMFS)
Carla Alvarez (intern,
Long Island University)
Divers:
Barry Smith (Dive Supervisor, NOAA-NMFS, Milford, CT)
Mark Dixon (NOAA-NMFS,
Milford, CT)
Andrew Draxler (Dive Supervisor, NOAA-NMFS, Sandy Hook, NJ)
Mike Smits (RanDive,
Inc., Perth Amboy, NJ)
Chuck Graves (RanDive, Inc., Perth Amboy, NJ)
Larry Nelson (RanDive, Inc.,
Perth Amboy, NJ)
Keith Makowski (RanDive, Inc., Perth Amboy, NJ)
Dave Lamon (RanDive, Inc.,
Perth Amboy, NJ)
Vessel support:
Mike and Joan Berko, F/V The Wizard
Scott Sirois, LT, Captain, R/V Gloria Michelle
Fred 'Fritz' Farwell, R/V Gloria Michelle
Chadwick Brown, LTJG, R/V Gloria Michelle and Captain, R/V Nauvoo
Russell Haner, LTJG, R/V Gloria Michelle
Scott Wingerter, LTJG, R/V Gloria Michelle
Kenneth Keene, R/V Nauvoo
James Hughes, Captain, R/V Walford
Pete Dutoit, R/V Walford
Deborah Dalton, R/V Walford
Robert Alix, Captain, R/V Loosanoff
Steven Pitchford, R/V Loosanoff
Warren Ihde, Captain, M/V Samantha Miller
Paul Bogan, Captain, M/V Samantha Miller
Charlie Curcio, M/V Samantha Miller
John Sullivan, M/V Samantha Miller
Glen Miller, Miller's Launch
Sven VanBatavia, Miller's Launch
Emily Christman, Commander, NOAA vessel Thomas Jefferson
Shep Smith, Officer in Charge, NOAA vessel Thomas Jefferson
Marc Moser, NOAA vessel Thomas Jefferson
Administrative support:
Patricia Irby (NOAA-NMFS)
Donna Sanchez (NOAA-NMFS)
LITERATURE
CITED
Able, K. W., and M. P. Fahay. 1998. The first year in the life of estuarine
fishes in the Middle Atlantic Bight. Rutgers University Press, New Brunswick,
NJ.
Able, K. W., and S. C. Kaiser. 1994. Synthesis of summer flounder habitat
parameters. NOAA Coastal Ocean Decision Analysis Series 1.
Adams, N. S., D. W. Rondorf, S. D. Evans, J. E. Kelly, and R. W. Perry.
1998. Effects of surgically and gastrically implanted radio transmitters
on swimming performance and predator avoidance of juvenile chinook salmon
(Oncorhynchus tshawytscha). Canadian Journal of Fisheries and
Aquatic Sciences 55:781-787.
Arendt, M., and J. A. Lucy. 2000. Seasonal residence, movement, and
activity patterns of adult tautog (Tautoga onitis) in lower
Chesapeake Bay. [Abstract]. Symposium on Tagging and Tracking Marine
Fish with Electronic Devices, University of Hawaii, Honolulu, HI.
Arendt, M. D., J. A. Lucy, and T. A. Munroe. 2001. Seasonal occurrence
and site-utilization patterns of adult tautog, Tautoga onitis (Labridae),
at manmade and natural structures in lower Chesapeake Bay. Fishery Bulletin
99:519-527.
Baras, E., and L. Westerloppe. 1999. Transintestinal expulsion of surgically
implanted tags by African catfish Heterobranchus longifilis of
variable size and age. Transactions of the American Fisheries Society
128:737-746.
Bégout Anras, M. L., D. Covès, G. Dutto, P. Laffargue,
and F. Lagardère. 2003. Tagging juvenile seabass and sole with
telemetry transmitters: medium-term effects on growth. ICES Journal of
Marine Science 60:1328-1334.
Bennetts, R. E., J. D. Nichols, J. D. Lebreton, R. Pradel, J. E. Hines,
and W. M. Kitchens. 2001. Methods for estimating dispersal probabilities
and related parameters using marked animals. Pages 3-17 in J. Clobert,
J. D. Nichols, E. Danchin, and A. Dhondt, eds. Dispersal. Oxford University
Press, Oxford, UK.
Bigelow, H. B., and W. C. Schroeder. 2002. Fishes of the Gulf of Maine,
3rd edition. B. Collette and G. Klein-MacPhee, eds. Smithsonian
Institution Press, Washington, D.C.
Bolden, S. K. 2000. Use of acoustic tracking to determine home range
of a coral-reef fish. [Abstract]. Symposium on Tagging and Tracking Marine
Fish with Electronic Devices, University of Hawaii, Honolulu, HI.
Bowen, B. W., and J. C. Avise. 1990. Genetic structure of Atlantic
and Gulf of Mexico populations of sea bass, menhaden, and sturgeon: influence
of zoogeographic factors and life-history patterns. Marine Biology 107:371-381.
Buckley, A., and G. Arnold. 2000. Orientation and swimming speed of
migrating plaice from acoustic tracking and ADCP measurements. [Abstract].
Symposium on Tagging and Tracking Marine Fish with Electronic Devices,
University of Hawaii, Honolulu, HI.
Butman, B., W. W. Danforth, S. C. Knowles, B. May, and L. Serrett.
2002. Seafloor topography and backscatter intensity of the Historic Area
Remediation Site (HARS), offshore of New York, based on multibeam surveys
conducted in 1996, 1998, and 2000. US Geological Survey Open-File Report
00-503 (DVD-ROM).
Colvocoresses, J. A., and J. A. Musick. 1984. Species associations
and community composition of Middle Atlantic Bight continental shelf
demersal fishes. Fishery Bulletin 82:295-313.
Chisholm, I. M., and W. A. Hubert. 1985. Expulsion of dummy transmitters
by rainbow trout. Transactions of the American Fisheries Society 114:766-767.
Collett, D. 2003. Modelling survival data in medical research, 2nd edition.
Chapman & Hall, NY.
Collins, M. R., J. C. McGovern, G. R. Sedberry, H. S. Meister, and R.
Pardieck. 1999. Swim bladder deflation in black sea bass and vermilion
snapper: potential for increasing postrelease survival. North American
Journal of Fisheries Management 19:828-832.
Comeau, L. A., S. E. Campana, and M. Castonguay. 2002. Automated monitoring
of a large-scale cod (Gadus morhua) migration in the open sea.
Canadian Journal of Fisheries and Aquatic Sciences 59:1845-1850.
Consensus Assessment Report. 2004. Assessment of the northern stock
of black sea bass. SARC 39. National Marine Fisheries Service, Woods
Hole, MA.
Cooke, S. J., B. D. S. Graeb, C. D. Suski, and K. G. Ostrand. 2003.
Effects of suture material on incision healing, growth and survival of
juvenile largemouth bass implanted with miniature radio transmitters:
case study of a novice and experienced fish surgeon. Journal of Fish
Biology 62:1366-1380.
Cote, D., D. A. Scruton, L. Cole, and R. S. McKinley. 1999. Swimming
performance and growth rates of juvenile Atlantic cod intraperitoneally
implanted with dummy acoustic transmitters. North American Journal of
Fisheries Management 19:1137-1141.
Cote, D., L. M. N. Ollerhead, D. A. Scrutoon, R. S. McKinley. 2003.
Microhabitat use of juvenile Atlantic cod in a coastal area of Newfoundland
determined by 2D telemetry. Marine Ecology Progress Series 265:227-234.
Cote, D., S. Moulton, P. C. B. Frampton, D. A. Scruton, and R. S. McKinley.
2004. Habitat use and early winter movements by juvenile Atlantic cod
in a coastal area of Newfoundland. Journal of Fish Biology 64:665-679.
Dyer, K. R. 1986. Coastal and estuarine sediment dynamics. John Wiley
and Sons, NY.
Egli, D. P., and R. C. Babcock. 2004. Ultrasonic tracking reveals multiple
behavioural modes of snapper (Pagrus auratus) in a temperate
no-take marine reserve. ICES Journal of Marine Science 61:1137-1143.
Eklund, A. M., and T. E. Targett. 1990. Reproductive seasonality of
fishes inhabiting hard bottom areas in the Middle Atlantic Bight. Copeia
4:1180-1184.
Eklund, A.-M., C. Koenig, and F. Coleman. 2000. Habitat utilization
and seasonal migrations of adult and juvenile jewfish, Epinephelus
itajara, using acoustic telemetry. [Abstract]. Symposium on Tagging
and Tracking Marine Fish with Electronic Devices, University of Hawaii,
Honolulu, HI.
Fabrizio, M. C., and S. R. Nelson. 1995. Find the fish: Using PROC
SQL to build a relational database for a mark-recapture study. Pages
238-243 in: SAS Institute, Client/Server Computing with
the SAS System: Tips and Techniques. SAS Institute, Inc., Cary,
NC.
Fleiss, J. L. 1981. Statistical methods for rates and proportions, 2nd edition.
John Wiley, NY.
Helm, W. T., and H. M. Tyus. 1992. Influence of coating type on retention
of dummy transmitters implanted in rainbow trout. North American Journal
of Fisheries Management 12:257-259.
Heupel, M. R., C. A. Simpfendorfer,
and R. E. Heuter. 2004. Estimation of shark home ranges using passive
monitoring techniques. Environmental
Biology of Fishes 71:135-142.
Hood, P. B., M. F. Godcharles, and R. S. Barco. 1994. Age, growth,
reproduction, and the feeding ecology of black sea bass, Centropristis
striata (Pisces: Serranidae), in the Eastern Gulf of Mexico. Bulletin
of Marine Science 54:24-37.
Hooge, P. N., and S. J. Taggart. 1998. Pacific halibut in Glacier Bay
National Park, Alaska. Pages 6-8 in: M. J. Mac, P. A. Opler,
C. E. Puckett Haeker, and P. D. Doran, eds., Status and trends of the
Nation's biological resources, volume 2. U.S. Department of the Interior,
U.S. Geological Survey, Reston, VA.
Hoskonen, P., and J. Pirhonen. 2004. Temperature effects on anesthesia
with clove oil in six temperate-zone fishes. Journal of Fish Biology
64:1136-1142.
Lacroix, G. L., D. Knox, and P. McCurdy. 2004. Effects of implanted
dummy acoustic transmitters on juvenile Atlantic salmon. Transactions
of the American Fisheries Society 133:211-220.
Lowe, C. G., D. T. Topping, D. P. Cartamil, Y. P. Papastamatiou. 2003.
Movement patterns, home range, and habitat utilization of adult kelp
bass Paralabrax clathratus in a temperate no-take marine reserve.
Marine Ecology Progress Series 256:205-216.
Marty, G. D., and R. C. Summerfelt. 1986. Pathways and mechanisms for
expulsion of surgically implanted dummy transmitters from channel catfish.
Transactions of the American Fisheries Society 115:577-589.
Morse, W. W. 1980. Reproduction of the summer flounder, Paralichthys
dentatus. Journal of Fish Biology 19:189-203.
Mulcahy, D. M. 2003. Surgical implantation of transmitters into fish.
Institute for Laboratory Animal Research Journal 44:295-306.
Munday, P. L., and S. K. Wilson. 1997. Comparative efficacy of clove
oil and other chemicals in anaesthetization of Pomacentrus amboinensis,
a coral reef fish. Journal of Fish Biology 51:931-938.
Musick, J. A.,and L. P. Mercer. 1977. Seasonal distribution of black
sea bass, Centropristis striata, in the Mid-Atlantic
Bight with comments on the ecology and fisheries of the species. Transactions
American Fisheries Society 106:12-25.
Neufeld, M. D., and C. R. Spence. 2004. Evaluation of a simple decompression
procedure to reduce decompression trauma in trap-caught burbot. Transactions
of the American Fisheries Society 133:1260-1263.
Olla, B. L., C. E. Samet, and A. L. Studholme. 1972. Activity and feeding
behavior of the summer flounder (Paralichthys dentatus) under
controlled laboratory conditions. Fishery Bulletin 70:1127-1136.
Packer, D. B., and T. Hoff. 1999. Life history, habitat parameters,
and essential habitat of Mid-Atlantic summer flounder. American Fisheries
Society Symposium 22:76-92.
Parsons, D. M., R. C. Babcock, R. K. S. Hankin, T. J. Willis, J. P.
Aitken, R. K. O'Dor, and G. D. Jackson. 2003. Snapper Pagrus auratus (Sparidae)
home range dynamics: acoustic tagging studies in a marine reserve. Marine
Ecology Progress Series 262:253-265.
Paukert, C. P., P. J. Chvala, B. L. Heikes, and M. L. Brown. 2001.
Effects of implanted transmitter size and surgery on survival, growth,
and wound healing of bluegill. Transactions of the American Fisheries
Society 130:975-980.
Peake, S. 1998. Sodium bicarbonate and clove oil as potential anesthetics
for nonsalmonid fishes. North American Journal of Fisheries Management
18:919-924.
Pollock, K. H., S. R. Winterstein, and M. J. Conroy. 1989a. Estimation
and analysis of survival distributions for radio tagged animals. Biometrics
45:99-109.
Pollock, K. H., S. R. Winterstein, C. M. Bunck, and P. D. Davis. 1989b.
Survival analysis in telemetry studies: the staggered entry design. Journal
of Wildlife Management 53:7-15.
Prince, A., and C. Powell. 2000. Clove oil as an anesthetic for invasive
field procedures on adult rainbow trout. North American Journal of Fisheries
Management 20:1029-1032.
Schreer, J. F., S. J. Cooke, and R. S. McKinley. 2001. Cardiac response
to variable forced exercise at different temperatures: an angling simulation
for smallmouth bass. Transactions of the American Fisheries Society 130:783-795.
Schwab, W. C., J. F. Denny, B. Butman, W. W. Danforth, D. S. Foster,
B. A. Swift, L. L. Lotto, M. A. Allison, E. R. Thieler, and J. C. Hill.
2000. Seafloor characterization offshore of the New York-New Jersey metropolitan
area using sidescan-sonar. U.S. Geological Survey, Woods Hole, MA. Open
File Report 00-295.
Shepherd, G. R., and M. Terceiro. 1994. The summer flounder, scup and
black sea bass fishery of the Middle Atlantic Bight and Southern New
England waters. NOAA Technical Report NMFS 122.
Sissenwine, M. P., R. R. Lewis, and R. K. Mayo. 1979. The spatial and
seasonal distribution of summer flounder (Paralichthys dentatus)
based on research vessel bottom trawl surveys. National Marine Fisheries
Service, Northeast Fisheries Science Center, Woods Hole Laboratory Reference
Document 79-55.
Steimle, F. W., and W. Figley. 1996. The importance of artificial reef
epifauna to black sea bass diets in the Middle Atlantic Bight. North
American Journal of Fisheries Management 16:433-439.
Summerfelt, R. C., and D. Mosier. 1984. Transintestinal expulsion of
surgically implanted dummy transmitters by channel catfish. Transactions
of the American Fisheries Society 113:760-766.
Summerfelt, R. C., and L. S. Smith. 1990. Anesthesia, surgery, and
related techniques. Pages 213-272 in: C. B. Schreck and P.
B. Moyle, eds., Methods for Fish Biology. American Fisheries Society,
Bethesda, MD.
Taylor, P. W., and S. D. Roberts. 1999. Clove oil: an alternative anaesthetic
for aquaculture. North American Journal of Aquaculture 61:150-155.
Tyus, H. M. 1988. Long-term retention of implanted transmitters in
Colorado squawfish and razorback sucker. North American Journal of Fisheries
Management 8:264-267.
US EPA. 1997. Supplement to the Environmental Impact Statement on the
New York dredged material disposal site designation for the designation
of the Historic Area Remediation Site (HARS) in the New York Bight Apex.
US Environmental Protection Agency, Region 2, New York, NY.
Wagner, G. N., E. D. Stevens, and P. Byrne. 2000. Effects of suture
type and patterns on surgical wound healing in rainbow trout. Transactions
of the American Fisheries Society 129:1196-1205.
Wigley, R. L., and R. B. Theroux. 1981. Atlantic continental shelf
and slope of the United States - macrobenthic invertebrate fauna of the
Middle Atlantic Bight region - faunal composition and quantitative distribution.
US Geological Survey Professional Papers (529-N):198.
Woody, C. A., J. Nelson, and K. Ramstad. 2002. Clove oil as an anesthetic
for adult sockeye salmon: field trials. Journal of Fish Biology 60:340-347.
Woolsey, J., M. Holcomb, and R. L. Ingermann. 2004. Effect of temperature
on clove oil anesthesia in steelhead fry. North American Journal of Aquaculture
66:35-41.
Wooster, G. A., H.-M. Hsu, and P. R. Bowser. 1993. A manual for nonlethal
surgical procedures to obtain tissue samples for use in fish health inspections.
New York Sea Grant and Northeastern Regional Aquaculture Center, University
of Massachusetts-Dartmouth.
