THE ABUNDANCE OF HARBOR SEALS IN THE GULF OF ALASKA

The abundance of harbor seals ( Phoca vitulina richardii ) has declined in recent decades at several Alaska locations. The causes of these declines are unknown, but there is concern about the status of the populations, especially in the Gulf of Alaska. To assess the status of harbor seals in the Gulf of Alaska, we conducted aerial surveys of seals on their haul-out sites in August-September 1996. Many factors influence the propensity of seals to haul out, including tides, weather, time of day, and time of year. Because these "covariates" cannot simultaneously be controlled through survey design, we used a regression model to adjust the counts to an estimate of the number of seals that would have been ashore during a hypothetical survey conducted under ideal conditions for hauling out. The regression, a generalized additive model, not only provided an adjustment for the covariates, but also confirmed the nature and shape of the covariate effects on haul-out behavior. The number of seals hauled out was greatest at the beginning of the surveys (mid-August). There was a broad daily peak from about 1100–1400 local solar time. The greatest numbers were hauled out at low tide on terrestrial sites. Tidal state made little difference in the numbers hauled out on glacial ice, where the area available to seals did not fluctuate with the tide. Adjusting the survey counts to the ideal state for each covariate produced an estimate of 30,035 seals, about 1.8 times the total of the unadjusted counts (16,355 seals). To the adjusted count, we applied a correction factor of 1.198 from a separate study of two haul-out sites elsewhere in Alaska, to produce a total abundance estimate of 35,981 (SE 1,833). This estimate accounts both for the effect of covariates on survey counts and for the proportion of seals that remained in the water even under ideal conditions for hauling out.     

DIEL HAUL-OUT PATTERNS AND SITE FIDELITY OF HARBOR SEALS (PHOCA VITULINA RICHARDSI) ON SAN MIGUEL ISLAND, CALIFORNIA, IN AUTUMN

We studied the haul-out patterns and movements of harbor seals ( Phoca vitulina richardsi ) on San Miguel Island, California, from 23 October through 6 December 1982 by attaching a radio transmitter to each of 18 seals and monitoring their presence ashore with continuously scanning receivers. Seals hauled out at all hours although, on average, the largest proportion of tagged seals was ashore between 1300 and 1500 h. Median durations of haul-out bouts of individual seals ranged from 4.7 to 21.8 h; 81% of all haul-out bouts were less than 12 h and 3% were longer than 24 h. Eighty-one percent of the seals that were resighted at least twice used only the sites where they were tagged; two seals used two sites and one seal used three. Most seals were hauled out on fewer than 51% of the days sampled. On average, about 41% of tagged seals hauled out each day whereas an average of about 19% was hauled out during peak afternoon hours. Using telemetry data to correct a count of 412 seals made during an aerial survey, we estimated absolute abundance at about 2,168 seals; a modified Peterson mark-recapture model produced an estimate of about 1,445 seals.     

Factors Affecting Haul-Out Behavior of Harbor Seals (Phoca vitulina) in Tidewater Glacier Inlets in Alaska: Can Tourism Vessels and Seals Coexist?

Large numbers of harbor seals (Phoca vitulina) use habitat in tidewater glaciers in Alaska for pupping, breeding, and molting. Glacial fjords are also popular tourist destinations; however, visitation by numerous vessels can result in disturbance of seals during critical life-history phases. We explored factors affecting haul-out behavior of harbor seals at a glacial site frequented by tourism vessels. In 2008-10, we deployed VHF transmitters on 107 seals in Endicott Arm, Alaska. We remotely monitored presence and haul-out behavior of tagged seals and documented vessel presence with time-lapse cameras. We evaluated the influence of environmental and physical factors on the probability of being hauled out, duration of haul-out bouts, and as factors associated with the start and end of a haulout. Location, season, hour, and interactions of location by year, season, hour, and sex significantly influenced haul-out probability, as did ice, weather, and vessels. Seals were more likely to be hauled out with greater ice availability during the middle of the day, and less likely to be hauled out if vessels were present. Cruise ships had the strongest negative effect; however, most vessel types negatively affected haul-out probability. Haul-out duration was longest in association with starting on incoming tides, clear skies, no precipitation, occurring in the middle of the day, and ending in the late afternoon or evening. End of haulouts was associated with increasing cloud cover, low ice availability, and vessel presence; large-sized tourism vessels or all-vessel-types combined were significant predictors of ending a haul-out bout. Probability of being hauled out was highest in June, during pupping season. Potential disturbances of harbor seals could be reduced, enabling longer resting times for seals and fewer interruptions for nursing pups, if vessels focused the majority of visits to glacial habitat to before or after the hours of 08:00-17:00 or, less optimally, 09:00-16:00.     

Influence of time of day and month on Weddell seal haul-out patterns at the Vestfold Hills, Antarctica

A diurnal pattern in haul-out behaviour has been described for Weddell seals at McMurdo Sound, Antarctica, but regional and seasonal variations were previously unknown. Knowledge of activity patterns is important for standardising census methods and census data. This study quantified the diurnal pattern in haul-out behaviour of Weddell seals at the Vestfold Hills from October 1994 to March 1995. Sequential counts of seals on the ice showed that, between 0900 and 1930 hours, seal abundance differed up to 95%. Fewer seals were hauled out in the morning than in the afternoon. The maximum numbers of seals were hauled out at the warmest time of day. The diurnal cycle was less pronounced in the breeding season than in the moulting season. The findings indicated the importance of censusing Weddell seals after 1430 hours and before 1700 hours local time, especially in the moulting season. Correction factors are given for month and time of day. Received: 27 November 1996 / Accepted: 1 May 1997     

HAUL-OUT SELECTION BY PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDII): ISOLATION AND PERCEIVED PREDATION RISK

The potential for non-aquatic predators to influence habitat use by harbor seals ( Phoca vitulina ) in a nearshore marine environment was studied by examining haul-out site use and through an experimental approach. Distance from shore, distance to possible foraging depths, peripheral water depth, and haul-out areas were quantified for each haul-out. There was a positive relationship between the number of seals hauled out and the distance from shore for eight known haul-out sites. The hypothesis that harbor seals increasingly hauled out farther offshore to reduce predation risk was tested experimentally by measuring their response to a model of a potential terrestrial predator in comparison to a control object, and to disturbance by a human at one of the study sites. Harbor seals abandoned the haul-out in the presence of the predator model, but showed little response to the controls, suggesting they possess a threat image for terrestrial predators and avoid hauling out when it is perceived. These results support the hypothesis that harbor seals select isolated sites to reduce exposure to terrestrial carnivores.     

HAUL-OUT ACTIVITY OF RINGED SEALS (PHOCA HISPIDA) DETERMINED FROM SATELLITE TELEMETRY

The haul-out activity of 15 ringed seals ( Phoca hispida ) equipped with satellite-linked radio transmitters was studied in NW Greenland ( ca. 73°-78°N). Between 19 June 1997 and 30 June 1999, telemetry data on haulout activity were obtained by the "Land-Sea-Reporter" (LSR), "Time-at-Depth" (TAD), and "Timelines" (TIM) systems housed within the satellite transmitters. The haul-out activity (% of total time hauled out) reported by the TIM system, which is specifically designed for collecting haul-out data, was about 1.4 times higher than that inferred from the LSR, but only about 0.7 of that inferred from TAD data. The TIM were used to describe haul-out activity. A total of 1,011 d with TIM were obtained (64.5% of a total of 1,568 "seal-days" monitored) representing data from nearly an entire annual cycle. No differences were found in percentage of time hauled out per month among various age categories. At all seasons the haul-out time showed considerable individual variation. There were no trends in percentage of time hauled out per month during late summer, fall, and winter (August-February). During the High Arctic winter darkness (November-January) the percentage of haul-out per month ranged between 3.9% in an adult (SD = 2.44, range: 1.1%-5.7%, n = 3 mo) and 15.7% in a subadult (SD = 1.95, range: 13.7%-17.6%, n = 3 mo). From late March there was a significant increase in haul-out time. Between 1 and 30 June, when aerial surveys of basking ringed seals usually are conducted, the haul-out time (% per day) increased from about 25% to about 57%. No tendencies in diel haul-out activity were revealed.     

LONG-TERM TRENDS IN HARBOR SEAL NUMBERS AT TUGIDAK ISLAND AND NANVAK BAY, ALASKA

We conducted land‐based counts of harbor seals (Phoca vitulina richardii) and collected related environmental data at Tugidak Island (Gulf of Alaska, 1994–2000) and Nanvak Bay (Bristol Bay, 1990–2000) to estimate population trends and identify factors influencing counts. At Tugidak Island, the seal population declined substantially during molting from 1976 through the 1980s, stabilized in the early 1990s, and increased at a moderate rate (3.4%/yr, CI: 1.0%–5.8%) from 1994 to 2000. Pups and all seals ashore during pupping increased at higher annual rates of 5.4% (CI: 2.2%–8.8%) and 8.3% (CI: 4.5%–12.3%) from 1994 to 2000 at Tugidak Island. At Nanvak Bay seals declined in abundance between 1975 and 1990 but increased during the 1990s at 9.2%/yr (CI: 7.2%–11.3%) during pupping and 2.1%/yr (CI: 0.6%–3.6%) during molting. Date and time‐of‐day were significant covariates in all analyses. Factors that led to declines at Tugidak Island and Nanvak Bay have seemingly abated sufficiently such that these populations are currently increasing, though still greatly reduced from the 1970s. Index sites are useful adjuncts to aerial surveys, providing survey‐related information not always available from aerial counts, which is useful in survey design and data analysis.     

MOLTING PHENOLOGY OF HARBOR SEALS ON TUGIDAK ISLAND, ALASKA

We documented the progression and timing of the annual molt of harbor seals on Tugidak Island, Alaska, from 1997 to 1999. In all years the timing of molting differed among age-sex classes. Yearlings molted first, subadults second, adult females third, and lastly adult males. Timing of molting was nearly identical in 1997–1998, whereas in 1999 molting occurred three to six days later for all age-sex classes except yearlings. Estimated dates when peak proportions of each age-sex class were molting ranged from 2 August (yearlings) to 2 September (adult males). The number of seals hauled out was positively related to the proportion of seals in the molt and negatively related to the proportion of seals in the postmolt. Population trend estimates, based on aerial counts conducted during a narrow window within the molting period, are likely biased toward certain age-sex classes. Statistical models used to estimate trend include covariates to help account for within-year variation in seal numbers, but do not account for compositional changes that occur during molting. Population modeling may elucidate the effects of within-year population structure on trend estimates. Monitoring molting phenology at additional sites is necessary to determine the extent of geographic variation in molting.     

Haul-out and diving activity of male Atlantic walruses (Odobenus rosmarus rosmarus) in NE Greenland

During August-September 1989 and 1990, movements, haul out and dive activity of male Atlantic walruses ( Odobenus rosmarus rosmarus L.) were studied at a terrestrial haul-out site situated in an inshore foraging area in NE Greenland at 76± 30' N. Data were collected from direct observations of a group of about 50 males during August, including walruses that could be individually identified from natural markings, and from tracking of 8 adults equipped with satellite-linked radio transmitters during August-September. In both years, instrumented walruses hauled out for a total of 29.3% of the sampling time. In 1989, when ice floes were available for hauling out, the walruses spent 11% of the time on ice, whereas in 1990, when ice was absent from the study area, they only hauled out on land. Duration of haul-out periods, which did not differ between months or years, averaged 11 h (0.46 d) on ice (S.D. = 5.9, range: 1–29 h, n = 19 periods), and 38 h (1.6 d) on land (S.D. = 11.7, range: 13–64 h, n = 43). The walruses mainly hauled out during the afternoon and evening. Numbers hauling out on land during August were negatively correlated with wind direction, precipitation (rain) and wind-chill. In 1989, the duration of periods of absence from the terrestrial haul-out site (i.e. presumed foraging trips) averaged 206 h or 8.5 d (S.D. = 106.9, range: 48–412 h, n = 13), whereas, in 1990, such trips averaged only 81 h or 3.4 d (S.D. = 37.9, range: 24-156 h, n = 24), reflecting that walruses used the haul-out site more frequently when ice was absent. Direct observations of foraging walruses showed that they were submerged about 81% of the time.     

SEX AND AGE SEGREGATION BY PHOCA VITULINA CONCOLOR AT HAUL-OUT SITES DURING THE BREEDING SEASON IN THE PASSAMAQUODDY BAY REGION, NEW BRUNSWICK

The size and composition of groups of harbor seals at two haul-out sites were studied during the breeding season of 1989, in the Passamaquoddy Bay region of Atlantic Canada. Evidence of segregation both by age and sex was found in the distinct composition of the two groups. One group contained mainly males and no pups, and the other had a sex ratio not significantly different from one and contained pups. The proportion of females increased at the nursery site with the onset of birthing in the region while the proportion of males increased through the breeding season at the other site. No increase in the number of adults, in total, was detected over the study period, suggesting that sexual segregation and not a change in haul-out frequency was responsible for the disparity in the sex structure of the two groups. The proportion of juveniles was significantly greater at the male dominated site than at the nursery site.     

Maximum likelihood population size estimation of harbour seals in the Dutch Wadden Sea based on a mark–recapture experiment

1. The harbour seal population Phoca vitulina in the entire Wadden Sea was severely depleted due to a virus-epizootic during 1988. A comprehensive study on the population biology and activity patterns was subsequently initiated to design a management and conservation plan. The main objective of this study was to estimate harbour seal abundance in the different regions of the Wadden Sea.
2. We investigated the potential of a mark–recapture experiment using VHF radio-tags in combination with repeated aerial surveys to estimate the number of harbour seals in the Dutch part of the Wadden Sea. The number of harbour seals hauled-out and the presence of any radio-tagged seals was monitored during seven aerial surveys of all known haul-out sites in the Dutch Wadden Sea over the 1994 breeding season.
3. A maximum likelihood (ML) estimator was developed to infer the rate of tag-loss and the size of the local prepupping population.
4. The ML estimate of the number of harbour seals in the Dutch Wadden Sea was 1536 (95% confidence limits were 1225 and 2200). The corresponding maximum proportion of seals hauled-out was 68%.
5. The use of VHF radio-tags which can be monitored from the air provides a way of correcting aerial survey counts for the proportion of harbour seals hauled-out during the surveys. Since haul-out behaviour may be influenced by local conditions, such as exposure time of sand banks, we recommend this technique be repeated in other areas of the Wadden Sea rather than using the estimates from the current study in other areas.     

Satellite tracking of ringed seals Phoca hispida off northwest Greenland

We monitored movements and haul-out patterns of four ringed seals Phoca hispida , off Northwest Greenland between 5 June and 31 October 1988 using the Argos Data Collection and Location System When the seals were hauled out on fast ice their locations were accurately determined, but when they were at sea, few accurate locations were obtained, evidently because these seals spent little time at the surface between dives The seals remained within the fjord where they were tagged, and hauled out often to early July Thereafter, as fast-ice disappeared, they dispersed widely and spent less time hauled out Time of day had no significant effect on haul-out patterns Haul-out periods declined significantly from June to August and increased in September-October Satellite contact with one seal was lost after 16 d while the seal was still in the fjord in late June One seal travelled over 200 km southwest and was located 4 July in offshore waters of Smith Sound 30 d after instrumentation Another seal moved southeast along the Greenland coast where contact was lost after 49 d on 23 July The fourth seal moved north along the Greenland coast, hauled out regularly on ice, and returned south along the coast in late September and October after 181 d of contact with the satellite     

Mark-resight estimates of seasonal variation in harbor seal abundance and site fidelity

Monitoring trends in abundance of pinnipeds typically involves counting seals at terrestrial haul-out sites during the breeding season. Counts of seals made at other times of the year are typically lower; however, it is often unknown whether this is because fewer animals are present or whether lower counts simply reflect a reduction in haul-out probability. Here we illustrate how photo-identification data from an individual-based study of harbor seals (Phoca vitulina) can be used to estimate seasonal variation in abundance and site fidelity. Monthly data collected over a two-year period were analyzed using a mark-recapture mark-resight model accounting for individuals transitioning between observable and unobservable states. Levels of site fidelity were high throughout the year and abundance estimates showed no seasonal pattern. This suggests that individual seals used haul-out sites to the same extent throughout the year, and that peaks in counts during the breeding season are a result of seasonal changes in haul-out probability. The results of this study have implications for understanding population sub-structuring, gene flow and disease spread.     

Changes in haul-out use by spotted seals (<Emphasis Type="Italic">Phoca largha</Emphasis>) on Rebun Island,Hokkado, Japan,in response to controls on harmful animals

Harmful animal controls on spotted seals on Rebun Island have been conducted each spring since 2010 due to an increase in the number of seals and damage to local fisheries. To evaluate the influences of controls on seals, we used the numbers of haul-out sites and hauled-out seals, and photo-identification to study differences in the usage patterns of haul-out sites by seals before and after controls. As a result, two major changes were confirmed. Firstly, in spring after controls, the numbers of hauled-out seals at Northern Rebun (NR) greatly decreased, while at Bensashi (Ben) on the southern side of Rebun they greatly increased, compared to spring prior to controls. Secondly, the number of identified seals observed at both NR and Ben (NR-Ben) increased after controls, while most of the seals that changed to NR-Ben after controls were observed only at NR (NR-NR) before controls. Additionally, most of the seals using NR-Ben were observed year-round. The controls had a direct influence on reducing the numbers of seals in the controls area mainly during the period of controls. However, many seals that avoided the controls area used other haul-out sites, and the numbers of year-round-seals on Rebun increased after controls.     

The World’s Northernmost Harbour Seal Population–How Many Are There?

This study presents the first abundance estimate for the world’s northernmost harbour seal (Phoca vitulina) population, which resides in Svalbard, Norway, based on three digital stereoscopic photographic surveys conducted in 2009 and 2010. The counts from these high resolution 3D images were combined with a novel method for estimating correction factors for animals that were in the water at the time of the surveys, in which extensive behavioural data from radio-tagged harbour seals were used together with age distribution data to estimate the proportion of seals of various age and sex classes hauled out at the times of the surveys. To detect possible seasonal shifts in age distribution between surveys, lengths of hauled out seals were measured from the stereoscopic images. No body-length differences were detected between the surveys; but, this may be due to a high degree of sexual dimorphism exhibited in this population. Applying the modelled correction factors, a total of 1888 (95% CI: 1660–3023), 1742 (1381–3549) and 1812 (1656–4418) harbour seals were estimated for the surveys flown on 01 August 2009, 01 August 2010 and 19 August 2010, respectively. The similarity between the three survey estimates (despite significant differences in the number of animals actually counted on the photos from each survey effort) suggests that the variation in numbers of hauled out seals is reasonably accurately adjusted for by the haul-out probability model. The low population size, the limited spatial distribution of the population and its reduced genetic diversity make this population vulnerable to chance events, such as disease epidemics.     

A multivariate analysis of phenotype and paternity in male harbor seals, Phoca vitulina, at Sable Island, Nova Scotia

Understanding the links between phenotype and reproductive successis critical to the study of the evolution of mating systemsand life-history patterns. We examined the relationship betweenphenotype and mating success of male harbor seals (Phoca vitulinaconcolour) at Sable Island, Canada. Cluster analyses of eighttraits including mating success determined by genetic paternityanalysis, haul-out behavior, body mass, and mass change identifiedfour groups of males with distinct characteristics. The most successfulmales were of moderate body size, were rarely sighted alone,were associated with many different groups on shore, and weresighted on the haul-out relatively infrequently. Large malesthat hauled out frequently alone, previously thought to be sociallydominant, were less likely to be successful. Also less successfulwere smaller, younger males. Contrary to our hypotheses, andunlike most terrestrially breeding pinnipeds, body size and reproductiveeffort were not positively associated with mating success, and somesuccessful males appeared to spend considerable time foragingin deep water.     

Long-term variability in the abundance of Antarctic fur seals Arctocephalus gazella at Signy Island, South Orkneys

The number of Antarctic fur seals Arctocephalus gazella hauled out at Signy Island in the South Orkneys was monitored annually between 1977 and 2008. Over the study period seal abundance showed a tenfold increase, from a minimum of 1,643 seals in 1978 to a maximum of 21,303 in 1994. The majority of individuals observed were young adult males, likely to be migrants from South Georgia, with small numbers of female seals and only 65 pups recorded during the survey period. Variability in counts showed a similar pattern to Laurie Island, also in the South Orkneys archipelago, suggesting a similar annual immigration of seals to these two islands. The date of first seal arrival was correlated with the date of fast-ice breakout at Factory Cove, Signy Island, and years in which break out was exceptionally late (>21 December) corresponded with years of reduced seal abundance. While the presence of fast-ice during the early breeding season may currently inhibit the establishment of a major breeding population of fur seals at Signy Island, it is important that routine monitoring should continue, particularly in the light of current patterns of climate warming in the Antarctic.     

CORRECTING AERIAL SURVEY COUNTS OF HARBOR SEALS (PHOCA VITULINA RICHARDSI) IN WASHINGTON AND OREGON

Aerial surveys of harbor seals on land produce only a minimum assessment of the population; a correction factor to account for the missing animals is necessary to estimate total abundance. In 1991 and 1992, VHF radio tags were deployed on harbor seals ( n = 124) at six sites in Washington and Oregon. During aerial surveys a correction factor to account for seals in the water was determined from the proportion of radio-tagged seals on shore during the pupping season. This proportion ranged from 0.54 to 0.74. Among the six sites there was no significant difference in the proportion of animals on shore nor was there a difference in age/sex categories of seals on shore between sites. The pooled correction factor for determining total population abundance was 1.53. An additional 32 seals were radio tagged in 1993 at one of the sites used in 1991. Comparing data from the two years, we found no interannual variation. Aerial surveys of all known harbor seal haul-out sites in Washington ( n = 319) and Oregon ( n = 68) were flown during the peak of the pupping season, 1991–1993. The Washington and Oregon harbor seal population was divided into two stocks based on pupping phenology, morphometics, and genetics. Mean counts for the Washington inland stock were 8,710 in 1991, 9,018 in 1992, and 10,092 in 1993. Oregon and Washington coastal stock mean counts were 18,363 in 1991, 18,556 in 1992, and 17,762 in 1993. Multiplying the annual count by the correction factor yielded estimates of harbor seal abundance in the Washington inland stock of 13,326 (95% CI = 11,637–15,259) for 1991, 13,798 (95% CI = 11,980–15,890) for 1992, and 15,440 (95% CI = 13,382–17,814) for 1993. In the Oregon and Washington coastal stock the corrected estimate of harbor seal abundance was 28,094 (95% CI = 24,697–31,960) in 1991, 28,391 (95% CI = 24,847–32,440) for 1992, and 27,175 (95% CI = 23,879–30,926) for 1993.     

SUMMER HOME RANGE AND HABITAT SELECTION OF HARBOR SEAL (PHOCA VITULINA) PUPS

We studied the summer home range and habitat selection of harbor seal pups tracked using VHF radio telemetry along the coast of central Norway in 1997 and 1998. Median fixed kernel home range of six pups tracked in 1998 was 10.4 km² and the median core area was 1.2 km². One particular deep basin (>100 m deep) was highly selected, and extensively used by four of the pups, probably for feeding. An area adjacent to the deep basin also was selected, probably for haul outs. One pup spent most of the time in inshore, kelp forest areas. Shallow areas without kelp forest and exposed land were used least frequently, possibly because they did not provide suitable areas for feeding and to haul out. The seals hauled out more during calm wind and low tide than during rough wind and high tide. Seals seemed to haul out on intertidal rocks associated with islands, and alternated between several haul-out sites. We found no pattern in haul-out activity associated with age, time of day, air/sea temperature, cloud cover, or rainfall. In 1997, seven pups were tracked manually. These data were associated with methodological limitations, and they were used only to illustrate that these seals stayed mainly within the shallow, inshore, kelp forest area, indicating a possible difference in habitat use between years.     

Habitat use by harbour seals (Phoca vitulina) in a seasonally ice-covered region, the western Hudson Bay

Over the last few decades, the period of ice cover in Hudson Bay has decreased, owing to climate warming, with breakup occurring approximately 3 weeks earlier than it did 30 years ago. The trend towards lengthening of the open water season has led to speculation that ringed seal numbers would decline, but then harbour seals might become numerous enough to replace ringed seals in the diet of polar bears. The movement patterns of 18 harbour seals equipped with satellite-linked transmitters in the Churchill River estuary (western Hudson Bay) were examined, as well as the dive behaviour of 11 of these seals. During the ice-free period, seals followed a general central place-foraging strategy, making repeated trips between their haul-out site in the Churchill River estuary and nearshore areas (<20 km) near the river mouth and estuary. Seal behaviour changed significantly as ice started to form along the coast of western Hudson Bay: animals remained significantly farther from the Churchill River haul-out site and from the coast and performed longer and deeper dives. However, throughout the entire tracking period, whether ice was present or not, all animals restricted their movements to a narrow band of shallow coastal waters (<50 m depth) along a 600-km stretch of the western Hudson Bay coastline, centred on the Churchill River estuary haul-out site. This natural self-limitation to nearshore shallow waters could restrict the potential for the population to increase in size and replace ringed seals as a primary energy resource for polar bears.