Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations

Abstract

Polar bears (Ursus maritimus) have experienced substantial changes in the seasonal availability of sea ice habitat in parts of their range, including the Beaufort, Chukchi, and Bering Seas. In this study, we compared the body size, condition, and recruitment of polar bears captured in the Chukchi and Bering Seas (CS) between two periods (1986-1994 and 2008-2011) when declines in sea ice habitat occurred. In addition, we compared metrics for the CS population 2008-2011 with those of the adjacent southern Beaufort Sea (SB) population where loss in sea ice habitat has been associated with declines in body condition, size, recruitment, and survival. We evaluated how variation in body condition and recruitment were related to feeding ecology. Comparing habitat conditions between populations, there were twice as many reduced ice days over continental shelf waters per year during 2008-2011 in the SB than in the CS. CS polar bears were larger and in better condition, and appeared to have higher reproduction than SB bears. Although SB and CS bears had similar diets, twice as many bears were fasting in spring in the SB than in the CS. Between 1986-1994 and 2008-2011, body size, condition, and recruitment indices in the CS were not reduced despite a 44-day increase in the number of reduced ice days. Bears in the CS exhibited large body size, good body condition, and high indices of recruitment compared to most other populations measured to date. Higher biological productivity and prey availability in the CS relative to the SB, and a shorter recent history of reduced sea ice habitat, may explain the maintenance of condition and recruitment of CS bears. Geographic differences in the response of polar bears to climate change are relevant to range-wide forecasts for this and other ice-dependent species.

Traditional Knowledge about Polar Bears (<i>Ursus maritimus</i>) in Northwestern Alaska

“…Bears across the region appear to be in relatively good physical condition. These reports coincide with a recent study that observed no change in body condition and reproductive indices between polar bears captured in this region in 1986 -94 and those captured in 2008 -11 (Rode et al, 2014).…”

“…These reports converge with Western scientific observations that body masses and skull widths of adult males in the Chukchi Sea are among the highest of any reported for polar bears in the spring (Manning, 1971;Rode et al, 2014), including perhaps the largest male ever weighed in the spring, at 632 kg (USFWS, unpubl. data).…”

“…Hunters in this study indicated that ringed and bearded seals continue to be polar bears' preferred prey (Kalxdorff, 1997), and this view is similarly supported by diet estimates for this population based on fatty acid analyses of tissue samples from captured bears (Rode et al, 2014). Additionally, hunters reported stable ringed and bearded seal populations, which were also reported by Quakenbush et al (2011a, b) on the basis of body condition and reproductive data collected from harvested seals.…”

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

“…Polar bears use ice for migration, mating, and to prey on seals. With reductions in sea ice, the sea-ice habitat will shrink substantially and the numbers of both polar bears and ice-dependent seals are expected to decline (Loeng et al, 2005;Durner et al, 2009;Rode et al, 2014;Laidre et al, 2015). Polar bears may have to retreat to land, which will likely lead to increased starvation for lack of appropriate food and declines in abundance (Hamilton et al, 2014).…”

Establishing a definition of polar bear (Ursus maritimus) health: A guide to research and management activities

“…Fragmentation and decreased spatial and temporal availability of their sea ice habitat can have negative impacts on the accessibility of their primary prey, i.e., seals (Derocher, 2010;Durner et al, 2009;Wiig, 2005). For example, decreased hunting opportunities and availability of prey can lead to nutritional stress and reduced body size, and may affect reproductive success and survival (Molnár et al, 2011;Regehr et al, 2007;Rode et al, 2010Rode et al, , 2014. In some species, energetic stress may lead to suppression of the immune system and thereby increased mortality and reduced reproductive rates (e.g., Boonstra et al, 2001;Wayland et al, 2002).…”