Unusual Predation Attempts of Polar Bears on Ringed Seals in the Southern Beaufort Sea: Possible Significance of Changing Spring Ice Conditions

Abstract

In April and May 2003 through 2006, unusually rough and rafted sea ice extended for several tens of kilometres offshore in the southeastern Beaufort Sea from about Atkinson Point to the Alaska border. Hunting success of polar bears (Ursus maritimus) seeking seals was low despite extensive searching for prey. It is unknown whether seals were less abundant in comparison to other years or less accessible because they maintained breathing holes below rafted ice rather than snowdrifts, or whether some other factor was involved. However, we found 13 sites where polar bears had clawed holes through rafted ice in attempts to capture ringed seals (Phoca hispida) in 2005 through 2006 and another site during an additional research project in 2007. Ice thickness at the 12 sites that we measured averaged 41 cm. These observations, along with cannibalized and starved polar bears found on the sea ice in the same general area in the springs of 2004 through 2006, suggest that during those years, polar bears in the southern Beaufort Sea were nutritionally stressed. Searches made farther north during the same period and using the same methods produced no similar observations near Banks Island or in Amundsen Gulf. A possible underlying ecological explanation is a decadal-scale downturn in seal populations. But a more likely explanation is major changes in the sea-ice and marine environment resulting from record amounts and duration of open water in the Beaufort and Chukchi seas, possibly influenced by climate warming. Because the underlying causes of observed changes in polar bear body condition and foraging behaviour are unknown, further study is warranted.

Climate hotspots: key vulnerable regions, climate change and limits to warming

“…With such losses projected now to occur at substantially lower temperatures (ca 1.5-2.0°C), the extinction risk for this iconic species appears to be very high within the next half century. Detailed population-based observations (Schliebe et al 2008;Stirling et al 2008;Regehr et al 2010;Rode et al 2010) and projections (Durner et al 2009;Hunter et al 2010) confirm this inference.…”

Ringed Seals and Sea Ice in Canada’s Western Arctic: Harvest-Based Monitoring 1992–2011

“…Future and archived tissue samples from this study are excellent candidates for dietary analysis studies using techniques such as fatty acid signatures (Thiemann et al, 2007(Thiemann et al, , 2008 and stable isotopes (Kelly, 2000;Chambellant et al, 2012). Our sample of 100 seals per season from this core habitat location, arguably the most predictable and largest available harvest sample from the western Canadian Arctic, was sufficient to document clear temporal and ice-related trends in body condition of adult and subadult seals.…”

“…This was not the case for populations of bears in the South Beaufort or in Hudson Bay (Stirling et al, 1999, which have fluctuated or declined, respectively, likely as a result of reduced sea ice reductions and the concomitant lesser availability of seals. Specifically, Stirling et al (2008), on the basis of cannibalized and starved bears in the southern Beaufort Sea, concluded that polar bears were nutritionally stressed from 2004 through 2006. One possible explanation was a decadal-scale downturn in seal productivity , which was indeed apparent in our Masoyak seal data in those same years.…”

Potentiation of ecological factors on the disruption of thyroid hormones by organo-halogenated contaminants in female polar bears (Ursus maritimus) from the Barents Sea

“…Nevertheless, it is not only challenging to compute a parameter describing local sea ice extent but also very difficult to interpret its biological relevance for polar bears, such as the optimal sea ice cover needed for hunting. For example, the reduction of sea ice extent and duration have somewhat unknown consequences for the foraging behaviour of polar bears on ringed seals (Phoca hispida), and their primary prey (Stirling et al, 2007). Moreover, because of different hunting skills or experience of individuals (Stirling, 1974), identical sea ice condition can result in large inter-individual differences in fat store accumulation (i.e., body condition) of bears coming ashore once the sea ice melts (see Dyck and Kebreab, 2009).…”