Polar Bear Diets and Arctic Marine Food Webs: Insights From Fatty Acid Analysis

Abstract

Abstract. We used quantitative fatty acid signature analysis (QFASA) to examine the diets of 1738 individual polar bears (Ursus maritimus) sampled across the Canadian Arctic over a 30-year span. Polar bear foraging varied over large and small spatial and temporal scales, and between demographic groups. Diets in every subpopulation were dominated by ringed seals (Phoca hispida) and, in the eastern Arctic, secondarily by harp seals (Pagophilus groenlandica). Beluga whales (Delphinapterus leucas) were an important food source for bears in the High Arctic, which is consistent with previous anecdotal reports. Foraging patterns were most similar among neighboring subpopulations with similar prey assemblages, but also differed geographically within Western Hudson Bay. The sexual size dimorphism of polar bears had an important effect on foraging, as large bearded seals (Erignathus barbatus) and walruses (Odobenus rosmarus) were consumed most often by older, male bears, whereas ringed seals and, where available, harbor seals (P. vitulina) were most important to younger age classes. Larger, older bears also had the greatest dietary diversity, apparently because of their ability to include larger-bodied prey. During spring and summer, polar bears in some areas increased predation on migratory harp seals and beluga whales. In Western Hudson Bay, bearded seal consumption declined between 1995 and 2001 for both male and female bears and continued to decline among females up to the most recent sampling (2004). Ringed seal consumption in Western Hudson Bay increased between 1998 and 2001, perhaps in response to increased ringed seal productivity, but was not significantly affected by date of sea-ice breakup. Overall, our data indicate that polar bears are capable of opportunistically altering their foraging to take advantage of locally abundant prey, or to some degree compensating for a decline in a dominant prey species. However, in other areas polar bears are dependent on the availability of ringed and bearded seals. Recent population data suggest that polar bears with the most specialized diets may be most vulnerable to climate-related changes in ice conditions. The results of this large-scale, ecosystem-based study indicate a complex relationship between sea-ice conditions, prey population dynamics, and polar bear foraging.

Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity

“…However, subadults may be more likely to obtain food via scavenging. Previous studies suggest that polar bears do not always consume the entirety of their kills (Stirling & McEwan, 1975) which may be likely when prey are large, such as bearded seals which are more commonly preyed upon by adult males (Cherry, Derocher, Hobson, Stirling, & Thiemann, 2011;Thiemann, Iverson, & Stirling, 2008) and when foraging occurs simultaneous to mating (i.e., males may leave prey to pursue mates) as it does in the spring. Compared to subadults, adult females may scavenge less from adult males as a result of habitat segregation (Ferguson, Taylor, & Messier, 1997) to avoid infanticide or conflicts associated with mating season.…”

Characterization of forage fish and invertebrates in the Northwestern Hawaiian Islands using fatty acid signatures: species and ecological groups

“…Most recently, FA signature analysis has been advanced to quantitatively estimate diets of higher predators such as seabirds and mammals (quantitative FA signature analysis, QFASA; Iverson et al 2004, 2006, Beck et al 2007, Nordstrom et al 2008, Thiemann et al 2008, Tucker et al 2009). These diet estimations have been conducted in northern temperate to Arctic ecosystems (and/or in captivity) using a small (3 to 9) to relatively moderate (≤ 28) number of prey types.…”

Barents Sea polar bears (Ursus maritimus): population biology and anthropogenic threats

“…The main reason is the loss of the platform needed for hunting ice-associated prey (Stirling & Archibald 1977;Smith 1980;Derocher et al 2002;Thiemann et al 2008). Sea ice is also a platform for mating and travelling to and from terrestrial maternity denning areas Derocher et al 2011).…”