Rapid Environmental Change Drives Increased Land Use by an Arctic Marine Predator

Abstract

In the Arctic Ocean’s southern Beaufort Sea (SB), the length of the sea ice melt season (i.e., period between the onset of sea ice break-up in summer and freeze-up in fall) has increased substantially since the late 1990s. Historically, polar bears (Ursus maritimus) of the SB have mostly remained on the sea ice year-round (except for those that came ashore to den), but recent changes in the extent and phenology of sea ice habitat have coincided with evidence that use of terrestrial habitat is increasing. We characterized the spatial behavior of polar bears spending summer and fall on land along Alaska’s north coast to better understand the nexus between rapid environmental change and increased use of terrestrial habitat. We found that the percentage of radiocollared adult females from the SB subpopulation coming ashore has tripled over 15 years. Moreover, we detected trends of earlier arrival on shore, increased length of stay, and later departure back to sea ice, all of which were related to declines in the availability of sea ice habitat over the continental shelf and changes to sea ice phenology. Since the late 1990s, the mean duration of the open-water season in the SB increased by 36 days, and the mean length of stay on shore increased by 31 days. While on shore, the distribution of polar bears was influenced by the availability of scavenge subsidies in the form of subsistence-harvested bowhead whale (Balaena mysticetus) remains aggregated at sites along the coast. The declining spatio-temporal availability of sea ice habitat and increased availability of human-provisioned resources are likely to result in increased use of land. Increased residency on land is cause for concern given that, while there, bears may be exposed to a greater array of risk factors including those associated with increased human activities.

Drivers and Environmental Responses to the Changing Annual Snow Cycle of Northern Alaska

“…Sea ice loss has caused more polar bears to come ashore during summer (Atwood et al 2016;Rode et al 2015b), limiting their access to food (Rode et al 2015a) and elevating their risk of encountering humans. On Cooper Island, site of a longterm black guillemot study (see next sidebar), polar bears have become common late-summer visitors (Fig.…”

“…The amount of open water in autumn, in turn, is tied to warming of the Arctic's lower atmosphere, a process associated with Arctic amplification (e.g., Serreze et al 2009 and references therein). Decreases in sea ice extent (Stroeve et al 2012) have subsequently led to changes in polar bear distribution in late summer and autumn with some bears forced to terrestrial habitats on the NSA from their preferred sea ice (Atwood et al 2016;Stern and Laidre 2016). Other species, including seabirds (Divoky et al 2015) and marine mammals (Kovacs et al 2011), also have to adapt to late summer and early autumn decreases in sea ice extent north of Alaska.…”

Fatty acid‐based diet estimates suggest ringed seal remain the main prey of southern Beaufort Sea polar bears despite recent use of onshore food resources

“…Sea ice has historically been available to polar bears in the SB throughout the year, but in recent years the sea ice edge has retreated north of the continental shelf in the summer‐fall and toward deeper, less productive waters of the Arctic Ocean (Dunton, Goodall, Schonberg, Grebmeier, & Maidment, ). During the annual sea ice retreat, some SB polar bears have remained on the ice, while others have come ashore, with increasing proportions reported onshore since the year 2000 (Atwood et al, ; Schliebe et al, ).…”

Historical and potential future importance of large whales as food for polar bears

“…Polar bears also scavenge stranded remains of large whales that died from natural causes or human‐sourced mortality (Figure ; Herreman and Peacock ; Atwood et al . ). Despite this, there have been few attempts to evaluate the importance of large whales in the diet of polar bears or their possible role in the viability of polar bears under climate change.…”