Northeast Fisheries Science Center Reference Document 08-07
Northwest Atlantic Ocean Habitats Important
to the Conservation
of North Atlantic Right Whales
(Eubalaena glacialis)
by Richard M. Pace III and Richard L. Merrick
National Marine Fisheries Serv, Woods Hole Lab, 166 Water St, Woods Hole MA 02543-1026
Print
publication date April 2008;
web version posted May 5, 2008
Citation: PACE RM III, MERRICK RL. 2008. Northwest Atlantic Ocean Habitats Important to the Conservation
of North Atlantic Right Whales (Eubalaena glacialis). Northeast Fish Sci Cent Ref Doc. 08-07; 24 p.
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ABSTRACT
We provide a
spatial and temporal description of the habitats important to the conservation
of North Atlantic right whales (Eubalaena glacialis) in US waters of the
Northwest Atlantic Ocean. This analysis is based on the premise that the biological and physical feature of habitat essential to
the conservation of right whales in this region (i.e., the primary constituent
element [PCE] which a species needs to survive and reproduce) is the presence
of dense patches of calanoid copepods (notably Calanus
finmarchicus). Despite the general importance of copepods to the
marine food web of the region, only limited data are available to map the
distribution of dense copepod patches that constitute the PCE for foraging
right whales. Hence, we used right whale foraging areas as a proxy for the spatial
locations of these patches. Based on systematic sighting surveys for right
whales conducted from 1970 through 2005, we identified concentrations of
foraging right whales in US Atlantic waters north of 40° N latitude. These data were
then used to define Dynamic Area Management (DAM) zones, which indicated that
most of the area north of the Great South Channel on Georges Bank was used at
least seasonally for foraging. This region included seasonal foraging subareas
generally identified as Cape Cod Bay, Great South Channel, Northern Edge of
Georges Bank, Western Gulf of Maine, Wilkinson Basin, and Jordan Basin. Wilkinson and Jordan Basins are also considered essential to
the conservation of right whales because these two basins are source areas for
the dense copepod concentrations upon which right whales prey in US Northwest
Atlantic waters.
INTRODUCTION
Critical habitat
for the North Atlantic right whale (Eubalaena glacialis) was designated
under the U.S. Endangered Species Act in June 1994 (59 FR 28793, hereafter
referred to as the Rule) and included feeding areas that extended over parts of
Cape Cod Bay and the Great South Channel (Figure 1). The critical habitat
definition in the Rule was based primarily on right whale sightings data (M.
Payne, NOAA Fisheries, 2005, pers. comm.), and the Rule clearly noted that the
timing of right whale occupancy in the feeding areas coincided with the
abundance of copepods, which were concentrated by oceanographic forces (Wishner
et al. 1988, Brown and Winn 1989, Kenney et al. 1986, and Mayo and Marx 1990).
In the Rule, many of the features contributing to these concentrations were
described, including the persistent thermal front at the northern mouth of the
Great South Channel and the hydrographic density gradients that induce water
flow within Cape Cod Bay. Hence, while the critical habitat designation was
based largely on sightings of right whales, it was recognized that prey abundance
was a primary constituent element (PCE) for right whales in northeastern U.S. waters.
The principal prey items of right whales in the Northwest Atlantic Ocean are adult copepods, most notably Calanus finmarchicus, at high
densities. Occurrence of dense copepod patches is the most important
biological component of right whale habitat in New England waters (Watkins and
Schevill 1976, Wishner et al. 1988, 1995, Murison and Gaskin 1989, Mayo and
Marx 1990, Beardsley et al. 1996, Woodley and Gaskin 1996, Kenney 2001,
Baumgartner et al. 2003, Baumgartner and Mate 2003). Right whales frequently
feed on copepod aggregations at the surface (such as in Cape Cod Bay: see Mayo and Marx 1990), but foraging at depths where copepod densities are highest is the
more common feeding mode (Kenney et al. 1995, Baumgartner and Mate 2003). In
fact, high concentrations of copepods trigger foraging activities in right
whales. This has been deduced by measuring densities of copepods at the
surface in the path of actively foraging right whales (Mayo and Marx 1990), and
by detailed analyses of vertical profiles of right whale dives evaluated in
conjunction with vertical plankton sampling (Baumgartner and Mate 2003). Estimates
vary on the prey densities necessary to stimulate right whale foraging. For example,
Mayo and Goldman (1992) reported a feeding threshold of 4,000 zooplankters/m3 for right whales feeding in Cape Cod Bay, while Beardsley et al. (1996)
observed whale feeding in a patch of 330,000 organisms/m3.
Uncertainty about the actual threshold is unimportant, but a standard analysis
of metabolic needs suggests right whales require dense patches to survive
(Kenney et al. 1986). Right whale feeding and habitat studies show that right
whales focus their foraging activities in areas where physical oceanographic
features (e.g., water depths, currents and mixing fronts) operate to concentrate copepods (Wishner et al. 1988,
Mayo and Marx 1990, Murison and Gaskin 1989, Baumgartner et al. 2003, Jiang et
al 2007). For example, Baumgartner et al. (2003) found that spatial
variability in right whale occurrence in the Bay of Fundy and Roseway Basin was associated with water depth and the depth of the bottom mixed layer as C.
finmarchicus aggregated over the deepest water depths in these regions. In
this study, right whales occurred in areas where the bottom mixed layer forced
discrete layers of C. finmarchicus to be shallower in the water column,
allowing more efficient foraging by the whales. Hence, the features characteristic of right whales foraging habitat are a
combination of both:
- Biological Oceanography – specific areas of the Gulf of Maine (GOM)
that contain significant numbers of adult copepods such as C. finmarchicus (e.g., the Great South Channel), and
- Physical Oceanography – the hydrographic processes that
concentrate zooplankton densities above some threshold at an accessible depth that
allows efficient foraging (see Kenney et al. 1986, Mayo and Goldman 1992).
In
addition to foraging areas, other areas essential to the conservation of right
whales are the source areas that supply the copepod prey. Within the Gulf of Maine, two sources exist for C. finmarchicus: (1) the advection of copepods
into the Gulf of Maine via the Northeast Channel; and (2) the redistribution of
overwintering copepods to shallower depths from the deep-water Gulf of Maine basins (Durbin et al. 2003, Miller et al. 1998). While copepod sources outside
of the Gulf of Maine are not considered here, source habitats within US waters may
be essential to the development of suitable right whale prey concentrations, even
if these are located outside the primary foraging areas.
In this report,
we provide a spatial and temporal description of the important right whale
foraging habitats in US waters of the Northwest Atlantic. Ideally, we would
prefer to rely upon fine-scale information on the spatial and temporal
distribution of copepod prey in this region, but such data do not exist.
Instead, we provide a description of right whale foraging habitat usage based
on systematic right whale sighting surveys conducted from 1970 through 2005. We
also provide in Appendix 1, a literature review of information on the
distribution and abundance of calanoid copepods in the Gulf of Maine/Georges
Bank area.
METHODS
As noted
earlier, dense patches of calanoid copepods are essential
to the conservation of right whales in the Northwest Atlantic Ocean.
However, broad-scale plankton monitoring schemes have proved ineffective in
detecting the high concentrations usually present in the vicinity of actively
feeding whales. The alternative “whale centric” sampling approach, where
sampling occurs around foraging right whales, has proven to be the only
effective approach for detecting dense prey patches (M. Baumgartner, Woods Hole
Oceanographic Institution, Woods Hole, MA 02543). Given that right whales only
forage on dense copepod aggregations, the location of actively foraging right
whales provides a proxy for the distribution of dense copepod patches.
Available sightings
data on the occurrence of right whales in the western North Atlantic (Brown et
al. 2007) also provide insight into the spatial and temporal variability of
right whale foraging areas (and, hence, dense copepod distributions) in this
region. The high seasonal variability and modest inter-annual variability observed
in right whale distribution is presumed to reflect the variability in the concentrated
patches of their copepod prey, typically C. finmarchicus (Brown et al.
2001, Kenney et al. 2001).
Hence, to
describe spatial-temporal patterns of foraging right whales in the US Northwest
Atlantic waters, seasonal ‘maps’ are needed from sighting surveys, in which
presence‑absence data have been adjusted to a common unit of survey effort.
Although different sets of cetacean sightings surveys have been conducted in
the Georges Bank/Gulf of Maine area using similar survey designs, none of these
have adequate geographic and seasonal coverage to detect all potentially-important
right whale foraging habitats in the region. The Northeast Fisheries Science Center’s (NEFSC) right whale aerial survey program is the most complete, but
lacks multi-year coverage in the autumn and has only been operational since
2002. Hence, pooling of survey data sets from multiple sources would be necessary
to ensure synoptic coverage. However, these data sets cannot be standardized
for a number of reasons, including: (a) many of the platforms used in the surveys
have considerably different effective survey strip widths per linear mile surveyed;
and (b) it is impossible to evaluate the variable detection rates among
observers and platforms post hoc (McKenzie et al. 2006).
Nonetheless, presence-only
data, as distinguished from presence-absence data, can still provide insight
into habitat use (Ward 2007). Although the relative likelihood of presence
among adjacent areas searched with differing survey sightings effort cannot be
evaluated, each occurrence observation reflects at least some use[1].
Further, all occurrence data from qualified observers are equally valid.
Therefore, we used all data from qualified observers archived in the North
Atlantic Right Whale Consortium’s (NARWC) sightings database to infer right
whale foraging habitats and, by proxy, the distribution of dense copepod patches
(i.e., the PCE). Cole et al. (2007) describe the methods by which many of these
data were obtained from aerial surveys. Because the database includes many
sightings of one or two animals, which may not be as predictive of foraging
whales as larger groupings, a subset of occurrence data was selected that was
considered reflective of foraging animals. The selection protocol used was developed
by Clapham and Pace (2001) in their analysis of Dynamic Area Management zones.
Definition
of Spatial and Temporal Extent of Important Right Whale Foraging Areas in the
Gulf of Maine/Georges Bank Region
We analyzed all
live right whale sightings in the NARWC database observed during 1970-2005 in
the area north of 40° N[2] latitude and eastward to the edge of US EEZ (i.e., the Hague Line) for which
the number of whales seen was not missing (Figure 1). We observed 9,612
sighting events records involving 17,756 right whales for the entire study area
(Table 1). From this set, all sighting records qualifying as part of a possible
DAM event were extracted; a possible DAM event is triggered whenever there is a
sighting of >2 right whales sufficiently close to each other to achieve a
density of 0.04 right whales/nm2 (Clapham and Pace 2001). This
extraction encompassed 7,761 sightings events representing 15,395 whales. The
DAM protocol (Clapham and Pace 2001) was then applied to calculate the circular
core sightings area and, as necessary, circular zones joined. This provided
1,292 unique “pseudo-DAM” events (Table 1) that were subsequently mapped using
ARCView GIS software (Figure 2).
To characterize the
temporal distribution of foraging right whales, we plotted all DAM-qualified
sightings by month. Although unquantified, unequal survey coverage among
geographical zones and across months generated these data, we believe that
these plots can still be used to define coarse seasonal patterns of right whale
foraging habitats. Spatial concentrations of DAM events over repeated years
(i.e., 3 or more) were considered as candidates for Seasonal Management Areas
(Merrick et al. 2001).
RESULTS AND DISCUSSION
Spatial
Extent of Right Whale Foraging Habitat
The DAM sighting
areas (Figure 2) encompass a larger geographic area than reported by Merrick et
al. (2001) and Merrick (2005). For example, the recently detected area of
early winter use by right whales near the northern edge of Jordan Basin (Figure 2) is much broader than previously suspected. This basin is likely a
seasonally important foraging area, as well as a prominent source of the copepods
which subsequently become densely aggregated in the Great South Channel and Cape Cod Bay areas (Bucklin and Kocher 1996, Durban et al. 2003, Jiang et al. 2007).
The number of
DAMs varied among years (Figure 3 and Figure 4) and reflects both varying habitat use
by the whales and variability in annual sightings effort. Nonetheless, it seems
reasonable to assume that most areas in the Gulf of Maine/Georges Bank region (Figure
2) constitute right whale foraging habitat at some time during most years. As
such, right whale foraging habitat in the Gulf of Maine can be broadly defined spatially
as (Figure 5):
- Within the Gulf of Maine and its associated Bays (e.g., Cape Cod
and Massachusetts Bays), and is
- Northward of lines drawn diagonally from the southern corner of
the Great South Channel Critical Habitat Area (41.0° N latitude, 69.1° W
longitude)
- Northeastward to the EEZ/Hague Line (42.2° N latitude, 67.2° W
longitude) and
- Northwestward to the southern corner of Cape Cod, MA (41.7° N
latitude, 70.0 ° W longitude)
Sightings (and pseudo DAM events)
occur to the south and east of this area, but a pattern of repeated annual
observations is not evident in these areas. Typically, whales are sighted in
these areas in one year, but are not seen again for a number of years. Most
likely, these are sightings of migrating whales. There are also areas within this
region of the Gulf of Maine where few right whale sightings have occurred
(e.g., Georges Basin); this could be the result of lack of suitable foraging
habitat, but could also be the result of limited survey effort in these areas
during the times when right whales are present.
The region shown
in Figure 5 covers approximately 19,200 square nautical miles[3].
In this region, 17,291 individual right whales have been sighted between 1970
and 2005 (of the 17,756 right whales sighted in U.S. waters north of 40° N). This
includes 7,747 sightings (15,118 individual whales) that qualified as 1,255 DAM
events (Table 1).
Temporal
Extent of Right Whale Foraging Habitat
The right whale
foraging region depicted in Figure 5 is much more expansive than the two existing
Critical Habitat Areas (Figure 1). Although the Cape Cod Bay and Great South
Channel Critical Habitat Areas are primary right whale feeding areas where
copepod concentrations have been documented, the enlarged area in Figure 5 encompasses
additional places where right whales regularly forage during various times of
the year. Clearly, there is a strong seasonal component to the utilization of
this larger area as right whale foraging habitat (Figure 6, Table 2). Although
interpretation of any exact seasonal patterns is affected by the
disproportionate right whale survey effort among seasons and subareas within
the Gulf of Maine/Georges Bank region, some broad conclusions are tenable. It
is likely that the seasonal movement of right whales that occurs between winter
and early summer from Cape Cod Bay to the Great South Channel and then to the Northern
Edge of Georges Bank (Figure 6, monthly panels 1 through 6) reflects the seasonal
occurrence of dense copepod patches in these areas (Lynch et al. 1998). Based
on the seasonal movement patterns of right whales (Figure 6) and the available
literature on the distribution, abundance, and population dynamics of calanoid
copepods in the Georges Bank/Gulf of Maine region (Appendix 1), six areas are seasonally
important for right whale foraging (Figure 7):
- Cape Cod Bay Critical Habitat Area
- Great South Channel Critical Habitat Area
- Western Gulf of Maine
- Northern Edge Georges Bank
- Jordan Basin
- Wilkinson Basin
Each of these areas is defined by
a pattern of repeated DAM events over three or more years (particularly in the
past decade when more observations are available due to increased survey coverage.)
Note that the spatial boundaries provided in Figure 5 and Figure 6 are meant to be
approximate.
Cape
Cod Bay– This area exhibits high densities of copepods during winter, spring, and,
possibly, fall. Of the 17,257 right whale sightings in New England during 1970
through 2005, 7,498 were in Cape Cod Bay (Table 1). A total of 543 pseudo-DAM events occurred in this area, most
during January-April (Figure 6).
Great
South Channel – This
area has high copepod concentrations at depth, especially during March-July,
owing to bathymetric features and water circulation patterns. A total of 5,753 right whales were
sighted in the area during 1970-2005; this included 344 pseudo-DAMs. Most right
whale sightings occurred during April-June, but also in July in some years (Figure 6). Right whale use of the Great South Channel area is not nearly as uniform
as in Cape Cod Bay, but is widespread enough to indicate that the Channel is an
essential foraging area in almost every year.
Western Gulf of Maine - The Western Gulf of Maine possesses a
complex set of bathymetric features which markedly affect the spatial/temporal
concentration of copepods among years, based on the interannual variability in
right whale sightings. From 1970 through 2005, 1,749 right whale sightings
(including 153 pseudo-DAMs) occurred in this area, mostly during April-May and
July-October.
Northern Edge of Georges Bank – This area has high copepod densities at depth, especially during May-July, emanating
from physical features (e.g., currents and upwelling) which concentrate
late-stage copepods during spring and summer. Foraging right whales in this
area are thought to be following an eastward progression of dense copepod patch
development, which begins in late spring and early summer. A total of 408
individual right whale sightings have occurred in this area, including 32 pseudo-DAMs
(Table 1). The period of greatest occupancy is during May-July.
Jordan and Wilkinson Basins – These two basins serve as over-wintering
areas for copepods (see Appendix 1; Figure 10), which are then the source for most
of the copepod patches on which right whales forage during the following spring
and summer.
Wilkinson Basin serves as an over-wintering area for diapausing (resting/dormant stage) copepods, and also
as a foraging area for right whales in spring. The limited survey sightings
effort in the Basin during 1970-2005 documented 1,058 individual right whales,
including 104 pseudo-DAMs (Table 1). Surveys have repeatedly found
concentrations of right whales in this area during April-July (Figure 6).
Jordan Basin is also an overwintering
area for diapausing copepods. As well, right whale surveys conducted in this
area during the winter of 2004-2005 (perhaps the first winter surveys ever in
this Basin) sighted up to 24 foraging right whales at a time (NMFS unpubl. data[4]).
The limited survey efforts in the area during 1970-2005 recorded a total of 236
individual right whales, including 21 pseudo-DAMs (Table 1). The available
data suggest that Jordan Basin is an important right whale foraging area, at
least during August–October.
SUMMARY
Analyses of
right whale sightings data in US Northwest Atlantic waters indicate that
foraging habitat important to the conservation of North Atlantic right whales (Figure 5-Figure 7 and Figure 10) is much more expansive than that within the two current critical
habitat areas (Figure 1). This additional habitat includes areas where high
concentrations of calanoid copepods regularly occur during the year, as well as
areas where significant number of foraging right whales have been sighted. While
most of the Gulf of Maine/Georges Bank region (Figure 5) can be considered as right
whale foraging habitat, utilization of the region by right whales has a strong
seasonal component (Figure 6). Six areas in the region are seasonally important:
Cape Cod Bay (January-April), Great South Channel (April-June), western Gulf of Maine (April-May and July-October), Northern Edge of Georges Bank (May-July), Jordan Basin (August-October), and Wilkinson Basin (April-July). Both Jordan and Wilkinson Basins are also essential for right whales in that they serve as
overwintering areas for diapausing copepods, and are the source of the copepods
that right whales forage upon during the following spring and summer.
ACKNOWLEDGMENTS
We gratefully acknowledge the work of Cynthia Christman for
providing data and information on DAM activities. We also thank Lisa Conger
and Fred Wenzel for literature review, and Mary Colligan, David Gouveia, and
Mark Minton for reviews of earlier versions of this document. The manuscript benefitted
considerably from editorial comments by Fred Serchuk. Thanks to the US Coast Guard for funding support of the aerial surveys conducted by NMFS under Memorandum of Agreement NEC 2003-021. The flights were authorized under the NEFSC's MMPA/ESA permit No. 775-1600.
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Appendix I. Review of Copepod
Distribution and Abundance
in the Gulf of Maine/Georges Bank Region
The
biological and physical processes affecting the distribution, abundance, and
population dynamics of Calanus finmarhicus in the Gulf of Maine/Georges
Bank region have received increased attention in recent years (Greene et al.
2004). Genetically, C. finmarchicusin Northwest Atlantic
waters off Canada and the U.S. (i.e., in the Labrador Current, Gulf of St.
Lawrence, and Gulf of Maine/Georges Bank regions) constitute a single,
interbreeding population (Bucklin and Kocher 1996). Patterns of genetic
variation in C. finmarchicusin the western North Atlantic are
consistent with the hypothesis that copepods recruit to the Gulf of Maine/Georges
Bank region from “upstream” areas. Oceanographic circulation patterns[5] (Figure 8 and Figure 9) influence C. finmarchicus distribution and abundance patterns
in the following ways:
- Slope waters from the Scotian Shelf (Greene and Pershing 2000) which
enter the Gulf of Maine may transport considerable numbers of developing
copepodites originating from both the Gulf of St. Lawrence and the Scotian
Shelf (Plourde and Runge 1993, Conversi et al. 2001).
- Dense concentrations of C5-stage copepods overwinter in the deep
basins within the Gulf of Maine, especially in Jordan and Wilkinson Basins[6].
- Circulation patterns within the Gulf of Maine return some progeny
of copepods produced in the Gulf of Maine back to the Gulf of Maine deep basins, where these progeny overwinter and contribute to reproduction in the
following spring (Hannah et al. 1997, Harms et al. 2000).
- Circulation patterns in Cape Cod Bay entrain Calanus produced elsewhere.
- During spring, circulation patterns within the Gulf of Maine, in conjunction with hydrographic processes and mixing fronts, concentrate
copepods north of the 100 m isobath at the northern end of the Great South
Channel (Wishner et al. 1995, Durbin et al. 1997, Kenney 2001).
- In early summer, continuous high-density aggregations of copepods
occur along the northern edge of Georges Bank.
- By late fall and winter, dense copepod concentrations are found
only in the deep-water basins.
Seasonal distributions and
general patterns of abundance of C. finmarchicus within the Gulf of Maine and Cape Cod Bay are well documented (e.g. Meise and O’Reilly 1996). However, the
geographic scales and depths at which copepods are sampled only rarely match
the fine-scale at which right whales forage (Mayo and Marx 1990, Baumgartner
and Mate 2003).
Much of our understanding of the
dynamics of copepods within the Gulf of Maine comes from the considerable
effort spent to understand the flow of Calanus that populates Georges Bank because of the importance of that area to valued fisheries. Relative to
copepod movement, Georges Bank is considered “down steam” of the Great South
Channel and, therefore, we can safely assume that major sources of Calanus to Georges Bank are important sources to the spring bloom in the Great South
Channel (Durbin et al. 2003). Briefly, 3 lines of support coalesce into
support for these 2 basins in particular as important retention areas: 1) water
circulation patterns, 2) Calanus population studies, and 3) combined
biological and physical oceanographic modeling studies.
Firstly, in addition to their
depth, there is reasonably strong circulation evidence that Jordan and
Wilkinson have their own circulation gyres nestled inside the larger-scaled
Gulf of Maine gyre (Figure 8 and Figure 9). Several cyclonic gyres characterize near
surface water flow in the Gulf of Maine, with limbs flowing toward, along and
around Georges Bank from both the western side and from Jordan and Georges Basins. Generally, the intermediate and deep circulation is isolated from Georges Bank (Lynch et al. 1998). Surface flow into the Gulf of Maine is primarily Scotian
Shelf water entering along the eastern side of the Northeast Channel, turning
around Cape Sable and Browns Bank, then joining the cyclonic gyres over Jordan and Georges Basins. Several gyres occur in the flow regime, north of Great South Channel
(the SCOPEX gyre), Wilkinson Basin and Georges Basin (Miller et al. 1998).
Together, this circulation, bottom topography features, and meteorological
phenomena control the water mass formation, movement and modifications
(Warn-Varnas et al. 2005).
Secondly, Miller et al. (1998)
provides an individual-based population model of C. finmarchicus for the
Georges Bank region. They demonstrated the importance of Georges Basin, with Wilkinson and Jordan Basins as sources to Georges. Durbin and Casas (2006)
summarize this the following way, “Local
sub-populations of C. finmarchicus can only occur in regions suitable
for diapause where it can complete its life cycle.” As for specific zones
within the Gulf of Maine, Miller et al. (1998) point to the MARMAP samples that
support Jordan and Wilkinson, and even suggest that Georges Basin may be a contributor. This has been debated due to the considerable water movement and
relative openness of Georges Basin to the shelf edge (Lynch et al. 1998).
Third, recent simulation models
that combine plankton sampling results of the last 2 decades and earlier,
robust circulation models of the Gulf of Maine and life history dynamics of C.
finmarchicus have corroborated earlier conclusions about the importance of
these basins as a copepod source the greater Gulf of Maine ecosystem (in
addition to the exogenous sources of the Scotian shelf and its sources). As
noted before, the Lynch et al.(1998) models supported all 3 deep basins
(Jordan, Wilkinson and Georges) as contributors of Calanus to Georges Bank (and therefore GSC). The models of Li et al. (2006) suggest that conditions
(copepod sources) within the Gulf of Maine are sufficient to account for the
early Calanus population of Georges Bank, and with the importance of
advected sources later in the year. The simulation models of Johnson et al.
(2006) also support the prominence of Jordan and Wilkinson Basins in the Calanus dynamics in the Gulf of Maine. They review other lines of
evidence that these are important retention areas primarily due to their depth
and Gulf of Maine circulation patterns.
Jordan and Wilkinson Basins were well known as overwintering areas for copepods and, in part, sources
for the spring copepod “bloom” that attracts right whales to the Great South
Channel each spring. For example, Bucklin and Kocher (1996) reviewed genetic
diversity among Calanus spp. stocks from locales and discovered
continuity among the Gulf of Maine Basins, Georges Bank and Scotian Shelf
source areas. This idea is reiterated often in the work of E. G. Durbin and
his colleagues (see Durbin 1997 for a review and more recently Saumweber and
Durbin 2006). Authors working in other areas of the North Atlantic also state
as a matter of general knowledge (e.g., without corroborating references) that Calanus overwinter at depth including depths well below the maximum occurring in Jordan
and Wilkinson Basins (see Gislason 2004 [actually sampled the Irminger Sea],
Heath et al. 2004, and Speirs et al. 2005, 2006). When reference to the annual
depth-to-surface cycle of C. finmarchicus is given, it is often to the
reviews of Hirche (1996a & b). The concept is well grounded in plankton
survey data that were collect in the preceding decades (e.g. Herman et al.
1991, which helps us understand some important habitat areas in Canadian waters
other than Bay of Fundy). Therefore, in addition to the areas where copepods
reach sufficient densities to provide forage for right whales, Jordan and Wilkinson Basins bounded approximated by the 200m isopleths represent habitats
important to conserving right whales (Figure 10).
