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Movement Patterns of Hooded Seals ( Cystophora cristata ) in the Northwest Atlantic Ocean During the Post-Moult and Pre-Breed Seasons

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Abstract and Figures

Movement patterns of hooded seals (Cystophora cristata) in the Northwest Atlantic in the pe-riod following moulting and prior to breeding are not well known. Here, we describe in detail the movement patterns of 21 seals for this period based on information gathered from satellite linked time depth recorders (SLTDRs). This study provides important baseline information necessary to understand the ecological requirements and patterns in habitat selection for the species. Adult and sub-adult hooded seals were tagged with SLTDRs directly after moulting in SE Greenland during July 2004, 2005 and 2007. Due to variation in tag date and arrival date to the breeding grounds, data between 1 Aug–28 Feb were used which gave all seals a track duration of 211 days (212 in 2005) except for one juvenile where the tag lasted for only 154 days. The tags yielded 36 107 loca-tion fixes (SD = 410.64, mean = 1 719.38). Although there was individual variation between seal trajectories during migration, the population shared a similar overall pattern. After moulting in July individuals travelled along the continental shelf area up to Davis Strait and Baffin Bay, thereafter moving southwards along the Labrador shelf until they arrived at the breeding grounds by March. Females tended to cut across the Labrador Sea and arrived at the Labrador shelf before heading up to the Baffin Bay area, while males tended to move straight there. The majority of the seals ended up at the Front (off Newfoundland and Southern Labrador) by March although a few of the tagged seals may have belonged to the Davis Strait breeding population and one male belonged to the Gulf of St. Lawrence breeding population. Seven seals displayed an eastward migratory pull and might have overlapped with the Northeast Atlantic population. This would support the theory of a panmitic population structure.
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Movement Patterns of Hooded Seals (Cystophora cristata) in
the Northwest Atlantic Ocean during the Post-Moult
and Pre-Breed Seasons
Julie M. Andersen and Yolanda F. Wiersma
Department of Biology, Memorial University of Newfoundland,
St. John’s, NL Canada E-mail:
Garry Stenson
Science Branch, Department of Fisheries and Oceans,
Northwest Atlantic Fisheries Centre, St. John’s, NL Canada
Mike O. Hammill
Dept. of Fisheries and Oceans
Mont Joli, Quebec. Canada
Aqqalu Rosing-Asvid
Greenland Institute of Natural Resources
Box 570, 3900 Nuuk, Greenland
Andersen, J. M., Y. F. Wiersma, G. Stenson, M. O. Hammill, and A. Rosing-Asvid. 2009.
Movement Patterns of Hooded Seals (Cystophora cristata) in the Northwest Atlantic
Ocean During the Post-Moult and Pre-Breed Seasons. J. Northw. Atl. Fish Sci., 42: 1–11.
Movement patterns of hooded seals (Cystophora cristata) in the Northwest Atlantic in the pe-
riod following moulting and prior to breeding are not well known. Here, we describe in detail the
movement patterns of 21 seals for this period based on information gathered from satellite linked
time depth recorders (SLTDRs). This study provides important baseline information necessary to
understand the ecological requirements and patterns in habitat selection for the species. Adult and
sub-adult hooded seals were tagged with SLTDRs directly after moulting in SE Greenland during
July 2004, 2005 and 2007. Due to variation in tag date and arrival date to the breeding grounds,
data between 1 Aug–28 Feb were used which gave all seals a track duration of 211 days (212 in
2005) except for one juvenile where the tag lasted for only 154 days. The tags yielded 36 107 loca-
tion xes (SD = 410.64, mean = 1 719.38). Although there was individual variation between seal
trajectories during migration, the population shared a similar overall pattern. After moulting in July
individuals travelled along the continental shelf area up to Davis Strait and Bafn Bay, thereafter
moving southwards along the Labrador shelf until they arrived at the breeding grounds by March.
Females tended to cut across the Labrador Sea and arrived at the Labrador shelf before heading up
to the Bafn Bay area, while males tended to move straight there. The majority of the seals ended
up at the Front (off Newfoundland and Southern Labrador) by March although a few of the tagged
seals may have belonged to the Davis Strait breeding population and one male belonged to the Gulf
of St. Lawrence breeding population. Seven seals displayed an eastward migratory pull and might
have overlapped with the Northeast Atlantic population. This would support the theory of a panmitic
population structure.
Keywords: Cystophora cristata, distribution, hooded seals, movement patterns, Northwest
Atlantic Ocean
J. Northw. Atl. Fish. Sci., Vol. 42: 1–11 Upload date 21 July 2009
J. Northw. Atl. Fish. Sci., Vol. 42, 2009–2010
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Fig 1. Reference map of the Northwest Atlantic showing locations mentioned in the text.
The hooded seal (Cystophora cristata) is an abun-
dant, pelagic, deep-diving pinniped distributed through-
out the North Atlantic and adjacent Arctic Oceans
(Sergeant, 1974; Folkow and Blix, 1995, 1999;
Hammill and Stenson, 2006). They breed synchronously
during mid- to late March on the pack ice around Jan
Mayen (“West Ice”), in Davis Strait between Bafn Is-
land and western Greenland, in the Gulf of St. Lawrence
(the “Gulf”) and off southern Labrador and/or northern
Newfoundland (the “Front”) (Fig. 1) (Sergeant, 1974,
1976; Hammill, 1993; Folkow et al. 1996). These four
breeding herds are considered to belong to two putative
populations (Hammill and Stenson, 2006). Hooded seals
whelping near Jan Mayen are thought to constitute the
Northeast (NE) Atlantic population while hooded seals
whelping and breeding in Davis Strait, the Gulf and
ANDERSEN et al.: Hooded Seal Movements 3
at the Front are all thought to belong to the Northwest
(NW) Atlantic population (Hammill and Stenson, 2006).
The total NW Atlantic population has been estimated
to consist of approximately 600 000 animals (593 500,
SE = 67 200, Hammill and Stenson, 2006), of which
90% are estimated to whelp at the Front (Stenson et al.,
2006). The NE Atlantic population is likely to number
between 70 000 and 90 000 animals, although there is
considerable uncertainty around these estimates due to
paucity of data and limited understanding of the relation-
ships between whelping areas (WGHARP, 2006).
Coltman et al. (2007) carried out a genetics study
across the two populations and found that the Greenland
Sea breeding herd was genetically most distant from the
NW Atlantic breeding areas; however, the difference
was statistically non-signicant. The results indicated
that the world’s hooded seals belong to a single panmitic
genetic population, thereby suggesting that there is some
overlap in distribution between the NE Atlantic and the
NW Atlantic populations. The herd belonging to the NE
Atlantic population and whelping around Jan Mayen dis-
perses to sea after breeding in March and some individu-
als return to the pack ice in the same area in July to moult
(Øritsland, 1959; Rasmussen, 1960) while the majority
moult further north (Folkow et al., 1996). Following
breeding, NW Atlantic hooded seals leave the whelp-
ing areas to feed and eventually migrate to the ice off
southeast Greenland where they moult in July (Stenson,
unpublished data; Sergeant, 1974). After moulting, the
general hypothesis has been that most of these animals
disperse across the NW Atlantic and up to Davis Strait
(Rasmussen, 1960) before migrating southward to the
whelping areas.
Preliminary studies have indicated that hooded seals
spend much of their time along the edges of the Cana-
dian and Greenland continental shelves or sea mounts
(e.g., Flemish Cap, Reykjanes Ridge) where they dive to
depths of over 1 500 m (Stenson and others, unpublished
data). Due to their pelagic distribution and the lack of
knowledge regarding their prey selection at various
times of the year, the extent of their sh consumption is
difcult to assess (Folkow et al., 1996). However, diet
studies indicate that adult hooded seals mainly forage
on benthopelagic species (Ross, MS 1992; Hammill and
Stenson, 2000; Haug et al., 2007). To a great extent, the
role of hooded seals in the marine ecosystem is virtu-
ally unknown. However, satellite telemetry allows us to
monitor movements of free ranging pinnipeds through-
out the year, providing data that have previously been
difcult to obtain.
Data from the tags provide us with valuable knowl-
edge of the general movement pattern for hooded seals
during the post-moult and pre-breed period which has
not been possible to obtain previously. Historical infor-
mation on marine mammal distributions was provided by
shore-based observations, incidental observations from
commercial hunting and capture of branded or tagged in-
dividuals (Rasmussen, 1960; Sergeant, 1974, MS 1979;
Hammill and Stenson, 2006). Although useful, these ob-
servations provide more information about the observer
effort then the actual distribution of the animals. Satellite
telemetry is therefore very valuable in terms of offering
continuous distribution information throughout the year
which can be projected onto a population level. Here the
movement patterns of 21 seals equipped with satellite
transmitters were examined for the post-moult and pre-
breed period (July–March) of their annual migration.
Adult and sub-adult hooded seals were tagged with
Satellite Linked Time Depth Recorders (SLTDRs) di-
rectly after moulting in July in SE Greenland (2004,
2005 and 2007) ( approx. 65°N 37°W). The animals were
captured using a net, weighed, and tranquilized using
tiletamine hydrochloride and zolazepam hydrochloride
(Telazol, AH. Robins Company, Richmond, VZ, USA)
administered intramuscularly (1 mg per 100 kg). The
SLTDRs were designed by the Sea Mammal Research
Unit (SMRU) in St. Andrews, Scotland. The transmit-
ters were attached to the head or neck of the seal, using
quick drying epoxy glue (Cure 5, Industrial Formulators
of Canada Ltd. Burnaby, BC Canada) and the seals were
released immediately upon recovery from the tranquil-
izer. The tag may last up to a year, and is lost when the
seal moults the following year.
Seal Locations
Locations at the surface were determined by the Ar-
gos system, and subsequently ltered using an algorithm
based on the travelling speed of the tracked animal, dis-
tance between successive locations and turning angle
(Freitas et al. 2008). We used the algorithms default
swim speed of of 2m/s.
Distribution maps (Figs. 2 and 3) were created using
ArcGIS 9.3 (Environmental Systems Research Institute,
Redlands, CA) where the points are represented by l-
tered locations of seal uplinks throughout their migra-
tion. Kernel density maps (Figs. 4 and 5) were created
using the package “spatstat” in R (version 2.8.0, The
R Foundation for Statistical Computing) and are based
on the total number of ltered uplink locations. These
density plots are created using a Gaussian kernel to cre-
ate smoothed histograms where “sigma” determines the
bandwidth of the kernel. Narrower bandwidths yield
J. Northw. Atl. Fish. Sci., Vol. 42, 2009–2010
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Fig 2. All 21 hooded seal tracks (ltered data) during the study period running from 1 Aug to 28 Feb which is the post-
moult pre-breeding migration period for this species. Dashed line is the 1 000 m contour line.
more extreme values and broader bandwidths narrow the
interquartile range. The bandwidth used for this study
was a sigma value of 0.75. The darker areas represent
locations where the presence of seals caused a higher
number of uplinks indicating more time spent in those
areas. The resolution of the grid is 20 000 meters.
A total of 26 seals with a post-moulting body mass
(BM) range of 73.5–194 kg were caught at approximate-
ly at 65°N 37°W in SE Greenland in July 2004, 2005 and
2007. Of the 26 seals tagged, 5 were excluded due to mal-
ANDERSEN et al.: Hooded Seal Movements 5
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Fig 3. Monthly movements of satellite
tagged hooded seals based on ltered
uplink data. Light grey symbols are
juvenile, darker grey female and black
are males. Dashed line is the 1 000 m
contour line.
J. Northw. Atl. Fish. Sci., Vol. 42, 2009–2010
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Fig 4. Kernel density surface map displaying the areas of high-use by hooded seals in the NW Atlantic Ocean during the
full post-moult pre-breeding migration period based on ltered uplink data. Dashed line is the 1 000 m contour
line. Resolution is 20 km.
function within one month of the actual tag date, yielding
a sample size of 21 seals (9 adult females, 8 adult males
and 4 juveniles (3 females and 1 male)). Data on the indi-
vidual seals are presented in Table 1 together with actual
tagging locations. Fig. 2 presents combined tracks for
the entire study period and Fig. 4 shows the high use ar-
eas averaged over the same period. One tag transmitted
for 154 days, whereas the rest lasted the entire study pe-
riod (18 tags = 211 days, 2 tags = 212 days (2005)). The
tags had a combined transmission period of 4 376 days
and provided (after ltering) 36 107 uplink xes (SD =
410.64), which gives an average number of 173.31 up-
links each day per seal. The mean total travel distance
throughout the period was 14 142.05 ± 2 038.92 km.
ANDERSEN et al.: Hooded Seal Movements 7
0750 1 500
Fig 5. Kernel density surface map display-
ing areas of high-use by hooded
seals in the NW Atlantic Ocean per
month during the post-moult pre-
breeding migration period (August–
February) based on ltered uplink
data. Dashed line is the 1 000 m con-
tour line. Resolution is 20 km.
J. Northw. Atl. Fish. Sci., Vol. 42, 2009–2010
Year PTT # Sex Wt (kg) Start End
2004 44444 F 116 01 Aug 28 Feb 211 66°15'N 34°17'W
2004 44487 M 155 01 Aug 03 Jan 154 66°08'N 34°35'W
2004 44443 F 85 01 Aug 28 Feb 211 66°10'N 34°27'W
2004 44489 M 172 01 Aug 28 Feb 211 66°09'N 34°30'W
2004 49539 F 81 01 Aug 28 Feb 211 66°15'N 34°17'W
2005 44486 F 112 01 Aug 28 Feb 211 65°28'N 36°13'W
2005 44450 M 127 01 Aug 28 Feb 211 65°31'N 36°21'W
2005 44448 F 90 01 Aug 28 Feb 211 65°29'N 37°00'W
2005 44488 F 138 01 Aug 28 Feb 211 65°30'N 36°19'W
2005 49540 M 194 01 Aug 28 Feb 211 65°31'N 36°14'W
2005 49530 M 146 01 Aug 28 Feb 211 65°25'N 36°37'W
2005 49533 F 138 01 Aug 28 Feb 211 65°20'N 37°03'W
2005 49531 F 95 01 Aug 28 Feb 211 65°20'N 37°06'W
2005 49537 M 174 01 Aug 28 Feb 211 65°25'N 37°01'W
2005 49534 F 117 01 Aug 28 Feb 211 65°19'N 37°11'W
2005 49535 F 98 01 Aug 28 Feb 211 65°19'N 37°11'W
2005 49529 F 114 01 Aug 28 Feb 211 65°22'N 37°20'W
2005 44503 M 109 01 Aug 28 Feb 211 65°23'N 37°22'W
2007 44417 F 73.5 01 Aug 29 Feb 212 65°26'N 37°18'W
2007 44419 M 97.5 01 Aug 29 Feb 212 65°23'N 37°48'W
2007 44425 F 130 01 Aug 29 Feb 212 65°23'N 37°55'W
TABLE 1. Year, Argos PTT identification number, sex, weight at tag date, start and end dates for
study period, days transmitted and tagging location of NW Atlantic hooded seals.
Due to different tag dates and arrival to the breed-
ing ground, the study period was selected to run from
1 August to 28 February.
The majority of the seals fanned out quite widely,
but in similar directions (across the Labrador Sea) im-
mediately after moulting (Fig. 3). The majority of fe-
males moved across the Labrador Sea to the Labrador
Shelf and Front area, while the males chose a more direct
route up to the Davis Strait and Bafn Bay area along the
continental shelf off western Greenland. Seven animals
stayed behind in Greenland for a longer period of time:
one female juvenile (#44443) stayed in the moulting area
throughout the migration period apart from a few shorter
trips along the SE Greenland coast and into the Denmark
Strait. This female never migrated to the breeding areas.
A young male (#44487) stayed behind in the moulting
areas until November, at which point he started to move
south, crossing the Labrador Sea towards the Front in
December. The signal was lost on 3 January 2005 when
the male was mid basin. Female #44488 moved north-
east into the Denmark Strait and did not migrate across
the Labrador Sea towards the Front until December.
This female then stayed in the Front area until breeding.
Male #44489 was the only seal to head straight north-
east through the Denmark Strait following the Green-
land shelf all the way up to the area off Danmark Havn
(~ 75º07'N 13º03'W). This male picked up speed in
October and headed south straight across the Labrador
Sea to the Front. Male #44503 migrated north following
the same pattern as #44489, but turned around and mi-
grated south of Iceland, along the Faeroe-Iceland ridge
and back on the north side of Iceland, ending up in the
Denmark Strait by the end of February. Male #49537
stayed in the moulting area the entire time until Febru-
ary when it abruptly migrated to the Front. Only one of
the tagged seals was a Gulf breeder (#49540) and was
the only male to cut straight across the Labrador Sea
after moulting to the Front before heading up along
the continental shelf area. This seal made a quick loop
into Bafn Bay before heading back down to the Front
by end of November and from there travelled south of
Newfoundland arriving in the Gulf of St. Lawrence by
the end of December. Males #44450 and #44419 ended
ANDERSEN et al.: Hooded Seal Movements 9
up in Davis Strait by end February indicating that they
were not breeding or they may have belonged to the Da-
vis Strait breeding herd.
Although the seals fanned out in various directions
in August, many of them gathered in Bafn Bay and
Davis Strait by October and November which may indi-
cate that these are important feeding areas for the popu-
lation (Figs. 3 and 5). The Labrador shelf, the Front and
SE Greenland may also be important habitat locations
for this species based on travel and kernel density pat-
terns (Fig. 5). The rest of the study area seemed to be
used for travelling or shorter foraging trips.
This study is the rst to illustrate the movement
patterns of the NW Atlantic hooded seals during their
post-moult, pre-breed migration. To date, there has been
limited information about the annual migration of this
species, but this study reveals that they travel large dis-
tances during this time. Although there is individual
variation in trajectories chosen, the overall picture of
how these animals move throughout the NW Atlantic
seem to be similar throughout the population. This dif-
fers somewhat to Folkow et al.’s (1996) ndings for the
NE Atlantic population’s migration pattern. They found
that the migrations of these seals to distant waters were
not synchronised in time and that they did not display a
general seasonal migration pattern (Folkow et al., 1996).
However, the NW Atlantic population did demonstrate a
similar pattern in choice of feeding areas and there was
general synchrony, with some individual variation. The
seals all started their migration after their annual moult
and seemed to head in various directions. However, most
start to come together in September along the continental
shelf, Davis Strait and in Bafn Bay (Fig. 3), presumably
for feeding as this is an important period for them to put
on weight after the moult and preparing themselves for
the whelping and breeding season. The choice of feed-
ing areas appear to be closely related to areas of high
topographic relief as the seals tend to stay close to the
1000 m contour line along the Labrador shelf area as
well as in the Bafn Bay basin. Bafn Bay and the east-
ern Canadian High Arctic have a complex coastline, an
inux of warm Atlantic water along the West Greenland
coast, and a restricted opening to the polar basin through
Robeson Channel (Heide-Jørgensen and Laidre, 2004) in
the north. This results in numerous microhabitats in the
region which may result in the high abundance of ani-
mals overwintering there (Heide-Jørgensen and Laidre,
2004). Some species which overlap with the range of
hooded seals in this area include marine mammals such
as beluga (Delphionpterus leucas), narwhal (Monodon
monoceros) and bowhead whales (Balaena mysticetus),
as well as various species of seabirds (Heide-Jørgensen
and Laidre 2004; Laidre et al., 2003, 2004, 2007). There
may be some overlap in prey preference between belu-
ga, narwhal and hooded seals (e.g., Greenland halibut
(Reinharditus hippoglossoides)) (Richard et al., 1998;
Laidre et al., 2004) in these areas. The aspects of how
oceanographic processes and prey distribution may drive
hooded seal habitat use (including their diving behaviour
throughout their migration) will be the subject of future
Areas along the Labrador shelf and the Bafn Bay
basin appear to be important feeding areas while the
Labrador Sea and the west coast of Greenland appear to
be areas where the seals move through at a higher speed
(Fig. 4). Even though the seals may have a wide move-
ment range during certain months (Fig. 3), the high-use
areas are actually rather small (Fig. 5). Some of the high-
use areas could be biased due to a higher number of seals
moving through a specic location during the month
resulting in a higher number of uplinks at a particular
point (e.g. Fig. 5: August is when the seals start mov-
ing out of the moulting patches which were located in
the same general area). It is not expected that hauling
out on ice will bias the results too much due to the fact
that the tags will stop transmitting if dry for more than
six hours. By September the seals arrived on the shelf
area in southern Davis Strait and in the southern Bafn
Bay basin. In October the seals appeared to spend more
time in the latter, while the movement range of the seals
during that month was very wide (Fig. 3). During the
month of November the seals display a more general use
of Bafn Bay and Davis Strait, and they started to move
south along the Labrador Shelf; by December they were
all south of Bafn Bay spending time in Davis Strait and
on the Labrador Shelf. That seals feeding in Bafn Bay
move south after November may be inuenced by the
build-up of ice in the area forcing the seals southwards.
Another possibility could be due to colder water temper-
atures forcing prey to deeper depths thereby increasing
the cost of feeding. January appears to be a month when
the seals stay in more restricted areas (Front and in the
Davis Strait) which could also be due to ice conditions,
while in February seals started to move across somewhat
longer distances again, perhaps to obtain a good position
for breeding. There was a high-use area in the southern
Denmark Strait which is caused by one seal’s intense use
of a small area that month. The rest of the seals were
spread out along the Front area and Labrador shelf up to
Davis Strait.
There appears to be a difference between sexes in the
initial choice of feeding areas. Females crossed the Lab-
J. Northw. Atl. Fish. Sci., Vol. 42, 2009–2010
rador Sea and arrived earlier onto the continental shelf
area off Labrador (Fig. 3, August), while males took a
more direct route up to Davis Strait and Bafn Bay. Be-
cause the hooded seal is a sexually dimorphic phocid,
the different choice in initial feeding area may be due
to different dietary requirements (Hammill and Stenson,
2000) after the moult. Recent studies have shown that
although there is an overlap between males and females
on a horizontal plane during feeding migrations after the
breeding season, they display differences in foraging
depths. Females tend to make more shallow dives than
males preceding the migration and deeper dives after the
migration (Bajzak et al., 2009). The feeding behaviour
and diving during post-moult and pre-breed seasons has
not yet been investigated; however this study indicates
that there is less horizontal overlap initially between
sexes during this period.
Two female juveniles (#49539 and #44417) migrat-
ed to Bafn Bay by the end of September, moving south
with the rest of the animals and ending up at the Front
by end of February. They may not have ended up at the
breeding patch by March, or they could possibly be rst
time breeders. Female #44486 arrived at the Front by the
beginning of February, but migrated back across the Lab-
rador Sea to Cape Farewell by the end. This may have
been a detour, or perhaps this female did not breed that
year. There is also a possibility that this female contin-
ued up to the West Ice where the NE Atlantic population
breeds in late March (e.g., Øritsland, 1959; Rasmussen,
1960).The seven seals which stayed behind in Greenland
for a longer period of time executing migrations up to
Denmark Strait and #44503 who travelled to Faroese
waters before ending up back in Denmark Strait by the
end of February offers a strong indication that there is an
overlap between the two populations, as has been sug-
gested in earlier studies (Rasmussen, 1960; Coltman et
al., 2007). The NE Atlantic population spends longer
periods of time in the Denmark Strait, around Iceland
and Jan Mayen (“West Ice”) and are found to be pres-
ent in waters off the Faeroe Islands during all months
of the year (Folkow et al., 1996). The ndings in this
study therefore support the genetic study carried out by
Coltman et al., (2007) who suggested that North Atlantic
hooded seals consists of one panmitic population.
This study provides new and valuable information
on the possible locations of critical habitat for hooded
seals. Further investigation of the telemetry data used
will include exploring how the physical environment af-
fects hooded seal migrations and their diving behaviour
throughout the full year. Such studies will improve our
understanding of the role this species play in the North-
west Atlantic ecosystem.
We would like to thank D. McKinnon and D.
Wakeham for help in capturing the seals and deploy-
ing the transmitters. Lise Langgård, Tore Haug, and
two anonymous reviewers provided valuable feedback
on an earlier draft of the manuscript. We would also
like to thank Roger Bivand at the Norwegian School
of Economics and Business Administration and the
LESA lab crew at Memorial University of Newfound-
land for valuable input. This work was funded through
the Atlantic Seal Research program, the International
Governance Program (DFO) and by Greenland In-
stitute of Natural Resources as well as a CFI grant
to YW.
SON. 2009. Intersexual differences in the postbreeding
foraging behavior of the Northwest Atlantic hooded
seal. Mar. Ecol. Progr. Ser., 385: 285–294. doi:10.3354/
HAUG, C. S. DAVIS, and T. L. FULTON. 2007. Pan-
mitic population structure in the hooded seal (Cystophora
cristata). Mol. Ecol., 16: 1639–1648. doi:10.1111/j.1365-
FOLKOW, L. P., and A. S. BLIX. 1995. Distribution and div-
ing behavior of hooded seals. In: A. S. Blix, L. Walløe and
Ø. Ulltang (eds.). Whales, Seals, Fish and Man. Elsevier,
Amsterdam, p. 193–202.
1999. Diving behaviour of hooded seals (Cystopho-
ra cristata) in the Greenland and Norwegian Seas. Polar
Biol., 22: 61–74. doi:10.1007/s003000050391
FOLKOW, L. P., P. E. MÅRTENSSON, and A. S. BLIX. 1996.
Annual distribution of hooded seals (Cystophora cristata)
in the Greenland and Norwegian Seas. Polar Biol., 16:
179–189. doi:10.1007/BF02329206
KOVACS. 2008. A simple new algorithm to lter marine
mammal Argos locations. Marine Mammal Science, 24:
315–325. doi:10.1111/j.1748-7692.2007.00180.x
HAMMILL, M. O. 1993. Seasonal movements of Hooded
seals tagged in the Gulf of St. Lawrence, Canada. Polar
Biol., 13: 307–310. doi:10.1007/BF00238357
HAMMILL, M. O., and G. STENSON. 2000. Estimated prey
consumption by harp seals (Phoca groenlandica), hooded
seals (Cystophora cristata), grey seals (Halichoerus gry-
pus) and harbour seals (Phoca vitulina) in Atlantic Can-
ada. J. Northw. Atl. Fish. Sci., 26: 1–23. doi:10.2960/J.
2006. Abundance of Northwest Atlantic hooded seals
(1960–2005). DFO Canada. Canadian Science Advisory
Secretariat Research Document 2006/068. 19 p. http://
STRØM. 2007. Diets of Hooded seals (Cystophora
ANDERSEN et al.: Hooded Seal Movements 11
cristata) in coastal waters and drift ice waters along the
east coast of Greenland. Mar. Biol. Res., 3: 123–133.
HEIDE-JØRGENSEN, M. P., and K. L. LAIDRE. 2004. De-
clining extent of open-water refugia for top predators in
Bafn Bay and adjacent waters. Ambio, 33: 487–494.
C. HOBBS, and O. A. JØRGENSEN. 2003. Deep-diving
by narwhals Monodon monoceros: differences in foraging
behavior between wintering areas? Mar. Ecol. Progr. Ser.,
261: 269–281. doi:10.3354/meps261269
JØRGENSEN, and M. A. TREBLE. 2004. Seasonal nar-
whal habitat association in the high Arctic. Mar. Biol.,
145: 821–831.
NIELSEN. 2007. Role of bowhead whale as a predator
in West Greenland. Mar. Ecol. Prog. Ser., 346: 285–297.
ØRITSLAND, T. 1959. Klappmyss (The hooded seal). Fauna
Oslo, 12: 70–90.
RASMUSSEN, B. 1960. Om Klappmyssbestanden i det nor-
dlige atlanterhav (on the stock of hooded seals in the
northern Atlantic). Fisken og Havet, 1: 1–23 (Fisheries
Research Board of Canadian Translation series No 387,
28 p., typescript).
AUBIN. 1998. Fall movements of belugas (Delphinapter-
us leucas) with satellite-linked transmitters in Lancaster
Sound, Jones Sound, and Northern Bafn Bay. Arctic, 51:
ROSS, S. A. MS 1992. Food and Feeding of the hooded seal
(Cystophora Cristata) in Newfoundland. M.Sc. Thesis
Memorial University of Newfoundland. St. John’s, New-
SERGEANT, D. E. 1974. A rediscovered whelping popula-
tion of hooded seals, Cystophora cristata Erxleben, and
its possible relationship to other populations. Polarforsc-
hung, 44: 1–7.
1976. History and present status of populations of
harp and hooded seals. Biol. Conserv., 10: 95–118.
MS 1979. Results of Tagging and Branding of Hood-
ed Seals, 1972–1978. International Commission for the
Northwest Atlantic Fisheries. ICNAF Res. Doc. 78/XI/86,
Serial No. 5302, 4 p.
GOSSELIN. 2006. 2005 Pup production of hooded seals,
Cystophora cristata, in the Northwest Atlantic. DFO
Canada. Canadian Science Advisory Secretariat Research
Document 2006/067, 44 p.
WGHARP. 2006. Report of the ICES/NAFO Working Group
on Harp and Hooded Seals. ICES, Copenhagen, 28 p.
... Despite being subject to population declines and displacements resulting from hunting, habitat destruction, environmental pollutants, interspecific competition and pathogens, the harbour seal has demonstrated a remarkable ability to recover and recolonize former ranges when efficient conservation measures have been implemented (Brasseur et al., 2018;Cammen et al., 2018;Härkönen et al., 2006;. Taken together, these observations might suggest that harbour seals, similar to other northern phocids, are characterized by a high dispersal ability and limited population structure (Andersen et al., 2009;Carr et al., 2015;Coltman et al., 2007;Davis et al., 2008;Fietz et al., 2016;Klimova et al., 2014;Thompson et al., 1996). However, this is not the case. ...
... This observation is supported by tagging data from both North Atlantic and North Pacific harbour seal populations, which demonstrate that harbour seals perform foraging trips of up to several hundred kilometers, but almost always return to the same haul-out site or region and very rarely cross large open stretches of deep water (Carroll et al., 2020;Dietz et al., 2013;Peterson et al., 2012;Rosing-Asvid et al., 2020;Small et al., 2006;Womble & Gende, 2013). In contrast, other northern phocid species, such as the sympatric grey seal, as well as the Arctic harp (Pagophilus groenlandicus), hooded (Cystophora cristata) and ringed seals (Pusa hispida), regularly undertake long distance migrations and/or movements covering thousands of kilometers and cross open water (Andersen et al., 2009;Nordøy et al., 2008;Svetochev et al., 2016;Thompson et al., 1996;Yurkowski et al., 2016). The open water barriers to harbour seal dispersal are particularly prominent in the North Atlantic, where population connectivity appears to be reduced by a heterogeneous The harbour seal's success in colonising new habitats is likely due to several factors, which may collectively facilitate the occupation of more predator-exposed, marginal and dynamic environments than other seal species. ...
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The harbour seal (Phoca vitulina) is the most widely distributed pinniped, occupying a wide variety of habitats and climatic zones across the Northern Hemisphere. Intriguingly, the harbour seal is also one of the most philopatric seals, raising questions as to how it colonised virtually the whole of the Northern Hemisphere. To shed light on the origin, remarkable range expansion, population structure and genetic diversity of this species, we used genotyping‐by‐sequencing to analyse ~13,500 biallelic SNPs from 286 individuals sampled from 22 localities across the species’ range. Our results point to a Northeast Pacific origin, colonisation of the North Atlantic via the Canadian Arctic, and subsequent stepping‐stone range expansions across the North Atlantic from North America to Europe, accompanied by a successive loss of genetic diversity. Our analyses further revealed a deep divergence between modern North Pacific and North Atlantic harbour seals, with finer‐scale genetic structure at regional and local scales consistent with strong philopatry. The study provides new insights into the harbour seal’s remarkable ability to colonise and adapt to a wide range of habitats. Furthermore, it has implications for current harbour seal subspecies delineations and highlights the need for international and national red lists and management plans to ensure the protection of genetically and demographically isolated populations.
... The hooded seal (Cystophora cristata) is an abundant, pelagic, deep-diving pinniped distributed throughout the North Atlantic and adjacent Arctic marine areas (Sergeant, 1974). Hooded seals spend most of the year dispersed and offshore, presumably foraging regularly outside the breeding and molting periods (Sergeant, 1974;Folkow and Blix, 1995;Folkow and Blix, 1999;Andersen et al., 2009). They breed synchronously during mid-to late March on the pack ice around Jan Mayen, in Davis Strait, in the Gulf of St. Lawrence (the Gulf), and off the northern coast of Newfoundland (the Front) (Sergeant, 1974;Hammill, 1993;Folkow et al., 1996;Bajzak et al., 2009). ...
... Habitats of hooded seals are difficult to survey during certain times of the year as they are inaccessible due to heavy pack ice, remoteness of those areas, and the requirement of expensive icebreaker ships and/or helicopters. Until now, information on hooded seal distributions has been provided by shore-based observations, capture of tagged individuals, vessel surveys, aerial surveys, and satellite telemetry methods (Sergeant, 1974;Hammill, 1993;Øritsland and Øien, 1995;Andersen et al., 2009). Significant gaps still exist in our knowledge about this species, some of which might be addressed using long-term passive acoustic monitoring (PAM). ...
The hooded seal is a migratory species inhabiting the North Atlantic. Passive acoustic monitoring (PAM) conducted over spatial scales consistent with their known and potential habitat could provide insight into seasonal and spatial occurrence patterns of this species. Hooded seal airborne and underwater acoustic signals were recorded during the breeding season on the pack ice in the Gulf of St. Lawrence in March 2018 to better characterize their acoustic repertoire (notably underwater calls). In-air and underwater signals were classified into 12 and 22 types, respectively. Signals produced by males through the inflation and deflation of the proboscis and septum were the predominant sounds heard on the ice surface. Five of the 22 underwater signals were proboscis and septum noises. The remaining underwater signals (17) were categorized as voiced calls and further analyzed using two classification methods. Agreement with the initial subjective classification of voiced calls was high (77% for classification tree analysis and 88% for random forest analysis), showing that 12–13 call types separated well. The hooded seal's underwater acoustic repertoire is larger and more diverse than has been previously described. This study provides important baseline information necessary to monitor hooded seals using PAM.
... The bulk of knowledge regarding the distribution of corals and sponges in Canadian waters is derived from random stratified research trawl surveys (Treble et al. 2000, Treble 2002and 2009, Wareham and Edinger 2007, Kenchington et al. 2010, complimented by opportunistic collections by Fisheries Observers on board commercial fishing vessels (Wareham andEdinger 2007, Wareham 2009 (Figure 16). ...
... Hooded seals are also highly migratory and spend their time at sea in between breeding and moulting seasons on sea ice. The Labrador Shelf acts as an important foraging area in between these seasons while the Labrador Sea acts as a migratory route (Anderson et al. 2009). For each age and sex class, Hooded seals utilize areas within the LSFA most during the fall (Figure 25). ...
Technical Report
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Foreword This series documents the scientific basis for the evaluation of aquatic resources and ecosystems in Canada. As such, it addresses the issues of the day in the time frames required and the documents it contains are not intended as definitive statements on the subjects addressed but rather as progress reports on ongoing investigations.
... Furthermore, sled dogs have been fed raw seal meat for centuries, if not millennia [73]. Several seal species are highly abundant and gregarious during the breeding and moulting season, and the ice-associated harp and hooded seals (Cystophora cristata) undertake annual long-distance migrations across the Atlantic Arctic [74,75]. Thus, sea ice provides many opportunities for pathogen transmissions and circulation both within and between terrestrial and marine mammals. ...
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Canine distemper virus (CDV) and phocine distemper virus (PDV) are major pathogens to terrestrial and marine mammals. Yet little is known about the timing and geographical origin of distemper viruses and to what extent it was influenced by environmental change and human activities. To address this, we (i) performed the first comprehensive time-calibrated phylogenetic analysis of the two distemper viruses, (ii) mapped distemper antibody and virus detection data from marine mammals collected between 1972 and 2018, and (iii) compiled historical reports on distemper dating back to the eighteenth century. We find that CDV and PDV diverged in the early seventeenth century. Modern CDV strains last shared a common ancestor in the nineteenth century with a marked radiation during the 1930s–1950s. Modern PDV strains are of more recent origin, diverging in the 1970s–1980s. Based on the compiled information on distemper distribution, the diverse host range of CDV and basal phylogenetic placement of terrestrial morbilliviruses, we hypothesize a terrestrial CDV-like ancestor giving rise to PDV in the North Atlantic. Moreover, given the estimated timing of distemper origin and radiation, we hypothesize a prominent role of environmental change such as the Little Ice Age, and human activities like globalization and war in distemper virus evolution.
... Most hooded seals from the West Atlantic (both the seals that whelp near Newfoundland and in Davis Strait) swim to Southeast Greenland during May-June and molt on the drift ice along the east Greenland coast in June-July. In August-September many of them pass through the assessment area, when they swim back to Davis Strait and Baffin Bay where they forage during winter (Andersen et al. 2009a). They prey mainly on large fish and squids and they regularly dive to more than 500 m (maximum recorded dive depth of 1652 m) (Andersen et al. 2013). ...
... A large fraction of the adult seals move into the Baffin Bay in September and until November they forage on the steep part of the shelfbreak in Baffin Bay (most of them will stay west of the assessment area). They mainly feed on large fish and squids (Andersen et al. 2009a) and they regularly dive deeper than 500 m (maximum recorded dive depth of 1652 m (Andersen et al. 2013). In spring they return to the whelping areas. ...
... The migration patterns of hooded seals are not well known. Recent data from satellite linked time depth recorders (SLTDRs) reveal that choice of feeding areas appear to be closely related to areas of high topographic relief (Andersen and Wiersma, 2009). This study also points out the important aspects of oceanographic processes and distribution of prey that might influence diving and migration behaviour. ...
... The trips performed by those animals lasted on average 47 ± 22 days (n = 46) (Folkow et al 1996). The northwest Atlantic subpopulation (Newfoundland and Labrador) have also been shown to travel large distances (Andersen et al 2009). During these migratory movements, seals have no access to fresh water. ...
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The purpose of this study was to investigate the total water turnover rate of fasting subadult hooded seals in order to elucidate to what extent these animals rely in seawater drinking/mariposia at this life stage. Considering mariposia is important for later accurate estimations of food consumption using water turnover rate as a proxy. Five subadult hooded seals were kept fasting for 4 days in a seawater pool. Total body water (39.6 ± 2.5 % of total body mass) decreased by 3.1 ± 0.4 % of initial body water over the experimental period. Turnover rates were 16.7 ± 3.9 (influx) and 24.6 ± 4.6 (efflux) ml·dayˉ1·kgˉ1 with a net water loss of 710±51 ml·day-1. It was estimated that the seals drank approximately 947 ml of seawater per day, which corresponds to 61 % of total daily water influx. Initial body water was relatively low as a result of the high body fat (46.9 ± 3.2 % of initial body mass) shown in the animals. It is concluded that subadult fasting hooded seals drink significant amounts of seawater during fasting. Although mariposia stands out as the major source of free water in fasting hooded seals, the amount of seawater ingested is unlikely to provide a net gain of free water as it is provided by metabolic water. However, it may contribute to excrete the excess of urea produced during early phase I of fasting. Keywords: marine mammals, mariposia, total body water, turnover rate, water homeostasis
... The marked seasonal environmental variation, represented by the extent of land fast ice, impacts also the presence and accessibility of animals (see also Flora et al. 2018). During autumn and winter, most birds will migrate southwards, which also applies to harp and hooded seals, the majority of narwhals and belugas, as well as baleen whales (Vibe 1950;Heide-Jørgensen et al. 2003;Dietz et al. 2008;Andersen et al. 2009;CAFF 2013;Grønnow 2016). From the hunt numbers reported by Piniarneq 2015, it becomes evident that the major Hg influx occurs during the 5 months from June to October, during which narwhals are present in the region and are the dominant caught species (73%). ...
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Despite the remoteness of the North Water, Northwest Greenland, the local Inughuit population is affected by global anthropogenic pollution and climate change. Using a cross-disciplinary approach combining Mercury (Hg) analysis, catch information, and historical and anthropological perspectives, this article elucidates how the traditional diet is compromised by Hg pollution originating from lower latitudes. In a new approach we here show how the Inughuits in Avanersuaq are subject to high Hg exposure from the hunted traditional food, consisting of mainly marine seabirds and mammals. Violation of the provisional tolerably yearly intake of Hg, on average by a factor of 11 (range 7–15) over the last 20 years as well as the provisional tolerably monthly intake by a factor of 6 (range 2–16), raises health concerns. The surplus of Selenium (Se) in wildlife tissues including narwhals showed Se:Hg molar ratios of 1.5, 2.3, and 16.7 in muscle, liver, and mattak, respectively, likely to provide some protection against the high Hg exposure. Electronic supplementary material The online version of this article (10.1007/s13280-018-1033-z) contains supplementary material, which is available to authorized users.
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Six adult belugas, Delphinapterus leucas, (2 males, 4 females) were instrumented with satellite-linked transmitters in Croker Bay, southeastern Devon Island in the Canadian High Arctic in mid-September 1995. Some days, the animals remained close to shore along the southeastern and eastern shoreline of Devon Island, presumably foraging for arctic cod (Boreogadus saida) and other prey. They spent the rest of the time in the deep waters of Lady Ann Strait, eastern Jones Sound, and the waters southeast of Coburg Island, presumably feeding on deepwater prey. Only males went farther north in waters off southeastern Ellesmere Island. The belugas' swimming speeds decreased in the later part of the study period. Their last transmissions came from the North Water, an area where belugas are known to winter. Results of this study were not sufficient to determine the extent of movement of belugas between the eastern Canadian Arctic and Greenland.
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Sexual dimorphism and different reproductive strategies lead males and females to forage differently among a wide range of species. We used dive and location data collected from 23 hooded seals Cystophora cristata captured in the Gulf of St Lawrence (Canada) during the period from March to June, 1992 to 2005, as proxies for foraging behaviour. Females spent 12 d longer than males in the Gulf before undertaking their migration to Greenland. Females and males greatly overlapped on a horizontal scale but were segregated on a vertical scale, females diving on average 70 m shallower than males during the few weeks preceding the migration and 40 m deeper than males following the migration. Both sexes spent similar amounts of time diving and showed significant diel variation in dive depth but remained at significant depths at night (>200 m), suggesting that both sexes foraged mostly on benthopelagic prey. The relatively minor differences in foraging behaviour observed between sexes may be explained by similar mass loss during the reproduction and the constraints related to the extensive annual migration.
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Variation in resource selection among sub-populations may elucidate differences in fitness and life history strategies. Specifically for top marine predators, differences in movements and behavior may result from responses to variation in a patchy, dynamic environment, Satellite-linked time-depth recorders (SLTDRs) were used to examine differences in narwhal Monodon monoceros diving behavior and habitat selection among 3 sub-populations in Canada and West Greenland (n = 16 individuals). The number of dives to different depths and time allocation within the water column was investigated in 3 seasons, with a focus on 2 discrete wintering grounds in Baffin Bay. Diving parameters were calculated from binned dive data and analyzed using repeated-measures mixed models accounting for temporal autocorrelation and individual variability. The number of surface dives (0 to 50 m) and time at the surface declined between summer and winter. Clear differences were observed between 2 wintering grounds. Whales occupying one wintering ground spent most of their time diving to between 200 and 400 m (25 dives per day, SE 3), confirmed by both depth and temperature recording tags. In contrast, narwhals in a separate wintering ground spent less time at shallow depths and most of their time diving to at least 800 m (13 to 26 dives per day, SE 1 to 3). A model of occupancy time at depth showed that whales making multiple daily deep dives spent over 3 h at >800 m (SD 0.6) and traveled 13 min (SD 1) per round trip to reach this depth, Whales diving to between 200 and 400 m spent approximately 2.5 h (SD 0.4) at this depth, traveling 5 min per round trip. The observed differences in time allocation and dive behavior indicate local variation between the 2 wintering grounds in the Baffin Bay ecosystem.
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To provide data on the feeding habits of hooded (Cystophora cristata) seals in the Greenland Sea, seals were collected for scientific purposes on expeditions with R/V"Jan Mayen", conducted in the pack ice belt east of Greenland in September/October 1999 and 2002 (autumn), July/August in 2000 (summer), and February/March in 2001 and 2002 (winter). Results from analyses of stomach and intestinal contents from captured seals revealed that the diet was comprised of relatively few prey taxa. The squid Gonatus fabricii and polar cod Boreogadus saida were particularly important, whereas capelin Mallotus villosus, and sand eels Ammodytes spp contributed more occasionally. G. fabricii was the most important food item in autumn and winter, whereas the observed summer diet was more characterized by polar cod, however with important contribution also from G. fabricii and sand eels. The latter was observed on the hooded seal menu only during the summer period, while polar cod, which contributed importantly also during the autumn survey, was almost absent from the winter samples. During the latter survey, also capelin contributed to the hooded seal diet. Samples obtained in more coastal waters indicated a more varied and fish based (polar cod, redfish Sebasetes sp., Greenland halibut Reinhardtius hippoglossoides) hooded seal diet.
We examined the spatial and temporal linkage between primary production, zooplankton distribution and density, and bowhead whale (Balaena mysticetus) foraging behavior in Disko Bay, West Greenland using concurrent ship-based oceanographic and net sampling together with instrumentation of whales with satellite- linked transmitters and dive recorders. Estimates of bowhead whale abundance were used in a bioenergetic model to calculate the potential consumption of zooplankton during their four-month stay in Disko Bay. Between 2001 and 2006, 30 whales were instrumented with satellite transmitters providing information on daily movements and fourteen whales were instrumented with archival Time-Depth or Time-Depth- Fluorescence recorders providing detailed dive data. Simultaneous data were collected on water column structure, phytoplankton and zooplankton density, taxa, and biomass at 25 stations south of Disko Island in 2003, 2005 and 2006. After the retreat of annual winter sea ice, bowhead whales explored a limited area along the south coast of Disko Island and had high interannual site fidelity. Mean dive depths varied between 53 (± 35) to 109 (± 41) m but maximum dive depths were >400 m. Most dives targeted the bottom and dive durations >40 min were observed for several whales. Available prey for bowhead whales was dominated by calanoid copepods, with Calanus finmarchicus, C. glacialis, and C. hyperboreus occurring at 90-100% of all stations between 0 and 50 m and contributing 78% ± 25 of the total biomass. Bottom sampling for epizooplankton in 2006 resulted in unprecedented densities of C. finmarchicus, several orders of magnitude higher than any other depths. Bioenergetic modeling indicated the population consumes ~220 tons of zooplankton per day or >21,000 tons during the 4-month stay in Disko Bay. Although the total biomass of zooplankton in the upper 50 m of the water column theoretically could support this predation level, benthic zooplankton densities and behavioral data suggest whales target pre-ascension stage epibenthic copepods in high density patches.
The ex istence is confirrned fr orn ae ri al survey of a whelping population of hooded seals in Davis Strait, reported in the nineteenth centur v, and numbering in the tens of thousands . This is believed to be the source of recruitment maintaining the population of hooded seals at icefields enst of Newfoundland where the species is heavily hunted. Locations and dates of tag and brand recoveries, frequent wandering of juveniles south of the regular range, and identity of breecling seasons al l suggest much mixing between populations in this species. Zusammenfassung: Durch Luftbeobachtung konnte die Existenz einer werfenden, einige Zehntausend Tiere zählenden Klappmützen-Population in Devis Strait bestätigt werden I Über die bereits im vergangenen Jahr­ hundert berichtet worden war. Es wird angenommen, daß die auf den Eisfeldern östlich von Neufundland stark bejagte Population aus diesen neu-nachgewiesenen Beständen eine ständige Auffrischung erfährt. Orte und Daten der Wlederfunda von durch Marken oder Brandzeichen gekennzeichneten Tieren, häufige Wan M dervorstöße von einzelnen Jungtieren südlich der Grenze regelmäßigen Vorkommens sowie die Dberein­ stimmung der Wurfzeiten deuten darauf hin, daß es zu einer starken Mischunq zwischen den Populationen dieser Art kommt. IntroducUon Hooded seals (Cystophora cristata Erxleben) are known to whelp during March-April in two areas of the North Atlantic: the larger population at the "West Ice " in the region of Jan Mayen Island, the sm aller, on pack ice northeast of Newfoundland, with a small fraction in the Gulf of St. Lawrence. The only known moulting areas are on pack ice east of Greenland in Denmark Strait, and from 74° to 76°N, in July-August (Fig. 1). What is known of the biology and relationship of these stocks was documented by 0ritsland (1959) and Rasmussen (1957, 1960). The present paper documents the rediscovery of a whelping ground arid discusses the interrelationships of stocks.
Hooded seals, Cystophora cristata, are abundant in the North Atlantic. This paper reviews current knowledge on the distribution and dive behaviour of these seals. The stock which breeds in sea ice near Jan Mayen may count about 250,000 animals, but little is known about where they stay and what they eat outside the pupping season (March/April) and the moult (July). We used satellite tags to monitor movements and/or dive depths and durations of 19 seals, and we obtained data on ≈12,000 locations and ≈120,000 dives, between July 1992 and July 1993. After the moult, most of the seals dispersed to travel, once or repeatedly, between the ice off Greenland and the distant waters off the Faeroe Islands, south of Bear Island, or the Irminger Sea. After breeding, all seals again returned to sea to travel to the waters off northern Ireland, the Faeroes or the Norwegian coast. Hooded seals may dive repeatedly to >1,000 m and stay submerged for >52 min, but usually dive to 100–600 m depth. We suggest that the dietary preferences, and even the fish consumption of hooded seals in different areas may be assessed by comparing their dive depths with the distribution of potential prey.