Deep into the ice: over-wintering and habitat selection in male Atlantic walruses

Freitas, Carla; Kovacs, Kit M.; Ims, Rolf A.; Fedak, Michael A.; Lydersen, Christian

doi:10.3354/meps07725

Cited by 45 publications

(56 citation statements)

References 40 publications

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“…In the winter, walrus distribution appears to be largely independent of ice cover and ice movement (Born et al 2005, Freitas et al 2009, Jay et al 2010. In summer, the variability in the numbers and proportions of the population at haulouts is high within and between years (Table 7) and there may be different drivers guiding haulout patterns for different age and sex classes.…”

Section: Survey Designmentioning

confidence: 99%

Use of Multiple Methods to Estimate Walrus (Odobenus rosmarus rosmarus) Abundance in the Penny Strait-Lancaster Sound and West Jones Sound Stocks, Canada

et al. 2014

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Atlantic walrus (Odobenus rosmarus rosmarus) occur in Canada in a number of largely discrete stocks (Born et al. 1995, DFO 2002, COSEWIC 2006, Stewart 2008. In the Canadian Arctic Archipelago there are three recognized stocks (NAMMCO 2006, 2011, Stewart 2008: the Baffin Bay stock, the West Jones Sound stock and the Penny Strait-Lancaster Sound stock. Within the range of each stock, walrus are widely distributed in the open-water season when they are found at sea and on ice or land in numbers from 1 to over 1,000. This widely spread but clumped pattern is a challenge to quantitative survey design. However, censusing haulouts is a well-established technique (Buckland and York 2009) for estimating the population size of pinnipeds (e.g. harbour seals, Phoca vitulina: Olesiuk et al. 1990, Thompson et al. 1997, Jacobs and Terhune 2000, Boveng et al. 2003, Reder et al. 2003, Gilbert et al. 2005, Cronin et al. 2007 1977 (290). Regression analysis of MCP and density (number of walrus divided by number of haulouts surveyed) showed no significant trends over time. We also calculated bounded count estimates for comparison. Finally, we used broad-scale behavioural data to estimate the proportion of the total stock that could be considered countable, to produce two adjusted estimates. We selected recent surveys with good coverage and ignored adjusted estimates that were lower than MCP. For the PS-LS stock, the adjusted MCP (with 95% CL) was 672 (575-768) and 727 (623-831) walrus in 2007 and 2009, respectively. For WJS, the best estimates were the adjusted MCP of 503 (473-534) in 2008 and the adjusted bounded count of 470 (297-1,732) in 2009. While both stocks appear to have remained stable over three decades, differences in survey coverage and possible differences in walrus distribution make precise population estimation difficult.

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Section: Survey Designmentioning

confidence: 99%

Use of Multiple Methods to Estimate Walrus (Odobenus rosmarus rosmarus) Abundance in the Penny Strait-Lancaster Sound and West Jones Sound Stocks, Canada

et al. 2014

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“…Hidden Markov model [58,59], first passage time [60], state space model [61,62]) and used to relate the defined horizontal ARS to particular structures of the environment (e.g. oceanographic features [31,53,63], sea ice [64,65], topography [66,67]). Bailleul et al [36] underlined the importance of integrating a vertical index of foraging effort to better identify foraging areas when studying deep-diving marine predators.…”

Section: Ecological Applicationsmentioning

confidence: 99%

From high-resolution to low-resolution dive datasets: a new index to quantify the foraging effort of marine predators

et al. 2015

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Background: In the last decade, thousands of satellite-relayed data loggers (SRDLs) have been deployed, providing large datasets on marine predator movement patterns at sea and their diving behaviour. However, the latter is in a highly summarised, low-resolution form, from which it is difficult to make the sorts of important behavioural inferences that are possible from higher-resolution datasets (such as detection of likely foraging events). The main objective of this study was to develop a simple, but accurate tool to detect and quantify within-dive foraging periods in low-resolution dives.Method: Two southern elephant seals were fitted with a head-mounted time depth recorder (TDR) (recording depth at 1 Hz) and an accelerometer (recording 3 axes of acceleration at 16 Hz) from which prey capture attempts were estimated (PrCA), and a Weddell seal was also fitted with a TDR (1 Hz).The resulting high-resolution dive profiles were used to: (1) calculate an accurate index of foraging effort based on the detection of vertical sinuosity switches (i.e. hunting highres time); (2) produce an SRDL-equivalent low-resolution dataset using a broken stick algorithm; and (3) from each low-resolution dive calculate a set of candidate foraging effort indices.Results: Hunting lowres time, which is the total time spent in decreased vertical velocity segments of the dive, was the foraging effort index that best correlated with hunting highres time. Hunting highres mode of SES dives (highly sinuous parts of high-resolution dives) was associated with 77 % of total PrCA. In comparison, Hunting lowres segments of SES dives were associated with 68 % of PrCA as well as with four times more PrCA than transit lowres segments. Conclusion:We found a low-resolution index which indicates foraging activity within a highly summarised dive profile and which identified most PrCA, despite degraded information transmitted by SLDRs. Used in combination with other measurements of the in situ environment, the hunting lowres index could be used in numerous integrated marine ecology studies, such as habitat use studies that are crucial to facilitate more effective conservation.

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“…We therefore suggest that Freitas et al (2009) have identified the breeding areas for these males during these two breeding seasons.…”

Section: Fig 4 Maximum Depth Of the Dives Recorded From Four Of The mentioning

confidence: 93%

“…The tag design was therefore adjusted prior to the 2003 summer season to include a protective ridge in front of the antennae (Fig. 2), which greatly improved the longevity of the tags Freitas et al 2009). …”

Section: Satellite Telemetrymentioning

confidence: 99%

“…Distribution, movements and habitat use Data from 17 of the newly-developed SRDLs were used to study movement patterns and habitat selection of adult male walruses instrumented in Svalbard in 2003(Freitas et al 2009). First-passage time (FPT) analyses were used to study habitat use and habitat selection was quantified using Mixed-effects Cox Proportional Hazards Models.…”

Section: 2mentioning

confidence: 99%

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Walrus Odobenus rosmarus research in Svalbard, Norway, 2000-2010

Lydersen

Kovacs

2014

NAMMCOSP

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Herein we report results from studies on walruses in Svalbard conducted in 2000-2010. Data from newly developed satellite relay data loggers (SRDLs) revealed seasonal differences in habitat use of adult male walruses. During winter, they moved into areas of >90% ice concentration, traveling as far as 600 km from ice-free water. Breeding areas deep into the pack ice were identified based on timing of the occupancy and diving behaviour. When the breeding season was over, walruses with SRDLs that were still transmitting locations returned to the coast, showing high site fidelity to the previous year’s summering area. Haul-out data from the SRDLs provided correction factors for an aerial survey of walruses that covered all known haul-out sites within the Svalbard Archipelago. This survey estimated 2,629 (95 % CI; 2,318 – 2,998) walruses to be in Svalbard during August 2006. Blubber biopsies from adult male walruses analyzed for fatty acids (FAs) showed vertical stratification similar to that observed in many other marine mammals. However, differences between layers were less pronounced, possibly because the thick dermis of walruses provides an insulating shield, affecting the FA composition of the outer blubber. The FA composition of the inner blubber most closely resembled the lipids in Mya truncata and Buccinum spp., which are considered the most important walrus prey in Svalbard. A study investigating the use of skin biopsies for assessing levels of organochlorines (OCs) in walruses found a significant relationship between OC levels in skin and blubber. Another contaminant study found a significant decrease in levels of PCBs and DDE in walruses in Svalbard from 1993 to 2002-04. Large inter-individual variation in OC levels was found, although all of the study animals were adult males from roughly the same location. In FA analyses of the inner blubber this variation appeared to be diet-related, with high OC levels having FA compositions in the inner blubber that closely matched seal tissues, while those with low levels matched typical invertebrate prey. Various enzymes, proteins, metabolites, minerals, and hormones were measured in blood samples to serve as baseline data for future health-related studies of both wild and captive walruses. Historical sex-distribution of walruses in southern Svalbard was investigated based on mandible measurements of individuals hunted during the 19^th century.The analyses showed that female walruses were once more common in south-eastern Svalbard than they are today.

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Deep into the ice: over-wintering and habitat selection in male Atlantic walruses

Cited by 45 publications

References 40 publications

Use of Multiple Methods to Estimate Walrus (<i>Odobenus rosmarus rosmarus</i>) Abundance in the Penny Strait-Lancaster Sound and West Jones Sound Stocks, Canada

Use of Multiple Methods to Estimate Walrus (<i>Odobenus rosmarus rosmarus</i>) Abundance in the Penny Strait-Lancaster Sound and West Jones Sound Stocks, Canada

From high-resolution to low-resolution dive datasets: a new index to quantify the foraging effort of marine predators

Walrus <i>Odobenus rosmarus</i> research in Svalbard, Norway, 2000-2010

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