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Gulf of Mexico
Resources Division by the GulfCet Program,
Department of Marine Biology Texas A&M University
at Galveston. In cooperation with the U.S.
Department of Interior, Minerals Management
Service.
Mexico data set is part of the overarching GulfCet
II study, Cetaceans, Sea Turtles and Seabirds in
the Northern Gulf of Mexico: Distribution,
Abundance and Habitat Associations, which provides
synoptic data and analyses on the species
diversity, abundance, and habitat characteristics
for cetaceans, sea turtles and seabirds in the
northern Gulf of Mexico. During two of the four
GulfCet II cruises, visual cetacean surveys were
conducted simultaneously with the collection of
data on the marine environment and zooplankton
biomass. Cetacean-habitat associations were
statistically analyzed for six physical and
biological oceanographic variables.
characterize cetacean habitat in the eastern Gulf
of Mexico. Correlation of environmental features
with sighting data may improve our understanding
of cetacean ecology and indicate which, if any,
physical and biological oceanographic variables
influence cetacean distribution.
report Cetaceans, Sea Turtles and Seabirds in the
Northern Gulf of Mexico: Distribution, Abundance
and Habitat Associations. Editors Randall W.
Davis, William E. Evans and Bernd Wursig.
Prepared under the U.S. Geological Survey,
Biological Resources Division by the GulfCet
Program, Department of Marine Biology, Texas A & M
University at Galveston, Galveston, Texas.
Biology
by technicians, graduate students, and data
management staff of GulfCetII program.
Northern Gulf of Mexico: Distribution, Abundance
and Habitat Associations.
Resources Division by the GulfCet Program,
Department of Marine Biology Texas A&M University
at Galveston. In cooperation with the U.S.
Department of Interior, Minerals Management
Service.
Resources Division Contract Number
1445-CT09-96-0004 and 1445-IA09-96-0009. This
report was prepared under contract between the
U.S. Geological Survey, Biological Resources
Division (BRD), Texas A&M University, and the
National Marine Fisheries Service. This report
has been technically reviewed by the BRD and the
Minerals Management Service (MMS), and has been
approved for publication. Approval does not
signify that the contents necessarily reflect the
views and policies of the BRD or MMS, nor does
mention of trade names or commercial products
constitute endorsement or recommendation for use.
It is, however, exempt from review and compliance
with the MMS editorial standards. Copies of the
report may be obtained from the Public Information
Office at U.S. Department of the Interior,
Minerals Management Service, Gulf of Mexico OCS
Region, Public Information Office (MS 5034), 1201
Elmwood Park Boulevard, New Orleans, LA
70123-2394, Telephone (504) 736-2519 or (800)
200-GULF.
was limited by small number of cetacean sightings,
dynamic hydrography of the Gulf, factors other
than hydrographic features that influence the
wide-ranging movements of cetaceans.
distribution and habitat characteristics, two
dedicated cruises aboard the R/V Gyre were
conducted in the eastern Gulf of Mexico in late
summer of 1996 (Gyre96G06) and mid-summer of 1997
(Gyre97G08). Simultaneous data were collected on
cetacean distribution, hydrography and zooplankton
biomass. In addition, the Gyre received near
real-time plots from the Colorado Center for
Astrodynamic Research of Sea Surface Height (SSH)
anomaly that identified hydrographic features such
as anticyclones and cyclones. This enabled the
investigators to direct the ship's course into
features that may have directly influenced the distribution of cetaceans or their prey.
by two teams of three observers during daylight
hours, weather permitting (i.e., no rain, Beaufort
sea state < 4) using standard vessel survey data
collection methods for cetaceans (Buckland et al.
1993). Each team had at least two members
experienced in shipboard cetacean observation and
identification techniques. Two observers searched
for cetaceans using 25x binoculars mounted on the
ship's flying bridge. The third observer
maintained a search of the area near the ship
using unaided eye or 7x hand-held binoculars, and
recorded data. The observers rotated through each
of these three stations every 30-40 minutes, and
each team alternated two-hour watches while there
was daylight. The vessel speed was usually 15
km/hr but varied with sea conditions. Sighting
effort was interrupted to approach a group of
animals to confirm identification, or due to
weather conditions. On-effort transect segments
located within a range of 5 km from each other
were considered as the same segment.
on large body size and deep diving ability (sperm
whales, category 2), intermediate body size and
dietary preference for squid (squid-eaters,
Category 3), phylogenetic relationship and
occurrence in deep water (<200 m) habitats
(bottlenose and Atlantic spotted dolphin Category
5). However, some species belong to more than one
category. For example, sperm whales and the
oceanic stenellids (pantropical spotted dolphin,
spinner dolphin, clymene dolphin and striped
dolphin) are also squid-eaters (Perrin et al.
1973, Clarke 1996, Ridgway and Harrison 1994).
Nevertheless, groups was necessary to reduce the
number of species and increase the sample size for
modeling with physiographic and hydrographic
variables. Cetacean sightings were grouped as
follows: 1) Cetaceans (all species identified) 2)
Sperm whales, 3) Squid-eaters (except for sperm
whales). Dwarf and pygmy whale, false killer
whale, melon-headed whale, pygmy killer whale,
Risso's dolphin, rough-toothed dolphin and all the
members of the Family Ziphiidae; 4) Oceanic
stenellids. Oceanic dolphins from the genus
Stenella: clymene dolphin, pantropical spotted
dolphin, spinner dolphin and striped dolphin but
not the Atlantic spotted dolphin; 5) Bottlenose
dolphins and Atlantic spotted dolphins.
multiple environmental variables were collected,
the presence of cetacean categories was modeled
with logistic regression for each cruise (Hosmer
and Lemeshow 1989). The environmental variables
used were bottom depth (m), bottom depth gradient
(m km-1), sea surface salinity (SSS, psu), dynamic
SSH anomaly (DHA, dyn cm), surface chlorophyll
concentration (micrograms L-1), and PMB (ccm-2).
Sea surface temperature was not used in the
analysis because of the almost uniformly warm
surface water in the Gulf during the summer.
Step-wise logistic regression was run using S-plus
4.5 software (Mathsoft 1997). Only deepwater
(depth > 800 m) stations that had values for all
environmental variables were used in the analysis.
As a result, not all species or species
categories had sufficiently large sample sizes for
each cruise.
Mexico, the presence of cetacean species or species groups was analyzed with a Chi-square test
for independence. Freeman-Tukey deviates were
calculated to determine the significant Chi-square
contribution in each class. The environmental
variables used in the analysis were ocean depth
and hydrographic features. On-effort transects
were divided into 18.5 km-long (10 nautical miles)
segments. If a segment of on-effort transect were
less than 9.25 km, it was added to the previous
segment. If it were greater than 9.25 km, it was
treated as a separate segment. A total of 2,351
transect segments were obtained from 14 cruises.
The mean segment length was 16.6 km+/1 5.61 S.D.
Cetacean categories were matched to their
respective transect segment.
Texas A&M University at Galveston
96G06 (October 1996) or mid-summer Gyre 97G08
(August 1997).
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
96G06 (October 1996) or mid-summer Gyre 97G08
(August 1997)
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
hydrographic data, dynamic cm
Texas A&M University at Galveston
Texas A&M University at Galveston
from hydrographic data, dynamic cm.
Texas A&M University at Galveston
Texas A&M University at Galveston
micronekton biomass in the depth interval 10-50 m,
cc m-2.
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
Texas A&M University at Galveston
GMT on Jan. 1, 4713 BC. This system of numbering
by consecutive days gives a calendar independent
of month and year and is used for analyzing
periodic phenomena. This system, devised in 1582
by J. Julius Scaliger and used most extensively by
astronomers, has no connection with the Julian
calendar other than the similar name.
Texas A&M University at Galveston
Texas A&M
Texas A&M University at Galveston
Division, Eastern Regional Office
successfully on a computer system at the U.S.
Geological Survey, no warranty expressed or
implied is made regarding the accuracy or utility
of the data on any other system or for general or
scientific purposes, nor shall the act of
distribution constitute any such warranty. This
disclaimer applies both to individual use of the
data and aggregate use with other data. It is
strongly recommended that these data are directly
acquired from a U.S. Geological Survey server, and
not indirectly through other sources which may
have changed the data in some way. It is also
strongly recommended that careful attention be
paid to the contents of the metadata file
associated with these data. The U.S. Geological
Survey shall not be held liable for improper or
incorrect use of the data described and/or
contained herein.
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