Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century

Abstract

The primary habitat of polar bears is sea ice, but in Western Hudson Bay (WH), the seasonal ice cycle forces polar bears ashore each summer. Survival of bears on land in WH is correlated with breakup and the ice-free season length, and studies suggest that exceeding thresholds in these variables will lead to large declines in the WH population. To estimate when anthropogenic warming may have progressed sufficiently to threaten the persistence of polar bears in WH, we predict changes in the ice cycle and the sea ice concentration (SIC) in spring (the primary feeding period of polar bears) with a high-resolution sea ice-ocean model and warming forced with 21st century IPCC greenhouse gas (GHG) emission scenarios: B1 (low), A1B (medium), and A2 (high). We define critical years for polar bears based on proposed thresholds in breakup and ice-free season and we assess when ice-cycle conditions cross these thresholds. In the three scenarios, critical years occur more commonly after 2050. From 2001 to 2050, 2 critical years occur under B1 and A2, and 4 under A1B; from 2051 to 2100, 8 critical years occur under B1, 35 under A1B and 41 under A2. Spring SIC in WH is high (>90%) in all three scenarios between 2001 and 2050, but declines rapidly after 2050 in A1B and A2. From 2090 to 2100, the mean spring SIC is 84 (±7)% in B1, 56 (±26)% in A1B and 20 (±13)% in A2. Our predictions suggest that the habitat of polar bears in WH will deteriorate in the 21st century. Ice predictions in A1B and A2 suggest that the polar bear population may struggle to persist after ca. 2050. Predictions under B1 suggest that reducing GHG emissions could allow polar bears to persist in WH throughout the 21st century.

Sustained disruption of narwhal habitat use and behavior in the presence of Arctic killer whales

“…Moreover, seals (ringed, harbor, and bearded), narwhal, and beluga, key prey species of killer whales in the ECA, are mesopredators, and there exists a potential for increased densities of killer whales to elicit structural changes to Arctic ecosystems mediated through both consumptive and trait-mediated mesopredator effects (3,72,73). Such structural changes are more likely in light of the predicted decline and possible loss of polar bears, the current apex predator, as sea ice is lost (42,43,(74)(75)(76).…”

Variation in Ringed Seal Density and Abundance in Western Hudson Bay Estimated from Aerial Surveys, 1995 to 2013

“…Without additional data to assess ringed seal haul-out behaviour over the survey period, it is difficult to determine whether the observed variation in seal densities is related to timing of the peak haul-out period or represents true changes in ringed seal abundance. The warming temperatures, reduced snow cover, changes in sea ice cover, and earlier ice breakup projected in various studies (Joly et al, 2010;Castro de la Guardia et al, 2013;Iacozza and Ferguson, 2014) are all likely to have significant negative impacts on ringed seals. The low density observed in 2013 suggests that ringed seal abundance has declined in recent years, or that survey design does not adequately account for the possibility of year-to-year variation in the timing of peak haul-out.…”

Population abundance and trends of Saltmarsh (Ammodramus caudacutus) and Nelson’s (A. nelsoni) Sparrows: influence of sea levels and precipitation

“…Species with limited geographic ranges, small population sizes, and habitat specializations are especially vulnerable to rapidly changing climate which may increase the risk of extinction for some taxa (Castro de la Guardia et al 2013;Li et al 2015). Identifying the specific aspects of climate change that affect population sizes and trends is a first but critical step in the assessment of how climate change will influence population persistence.…”