Chukchi Sea (CS)

First population estimate published in 2018, based on extrapolation of density in select part of the subpopulation area.

Status table outtake

Subpopulation size Subpopulation trend Sea ice metrics 1979-2018 Human-caused removals 2013/2014–2017/2018
Estimate and uncertainity Method and type of evidence Year and citation Long term (approx 3 generations) Short term (approx 1 generation) Change in date of spring ice retreat / fall ice advance (days per decade) Change in summer sea ice area (percent change per decade) 5-year mean
Quota (bears per year) Actual (% of total population)
2937
1552-5944
Physical C-R with density extrapolation2016Data deficientLikely stable (2008 to 2016)-6.3/6.8-25.958 (changed to 85 in July 2018)15.4 (0.5%) in U.S. + approx. 32 (1.1%) in Russia
See also the complete table (all subpopulations)

Comments, vulnerabilities and concerns

Estimate of subpopulation trend from Regehr et al. (2018b). Indices of good body condition and recruitment during springtime research, although autumn observations suggest declining cub survival.  Longer ice-free periods are increasing land use. Subsistence harvest is legal and monitored in US. Harvest remains illegal and un-monitored in Russia.

Status and delineation

Chukchi Sea subpopulation mapThe Chukchi Sea area. See also the complete map (all subpopulations).

Studies in the late 1980s and early 1990s revealed that polar bears in the Chukchi Sea (CS) subpopulation, also known as the Alaska-Chukotka subpopulation, are widely distributed on the pack ice of the northern Bering, Chukchi, and eastern portions of the East Siberian seas (Garner et al. 1990, 1994, 1995). Based upon these telemetry studies, the western boundary of the subpopulation was set near Chaunskaya Bay in northeastern Russia. The eastern boundary was set at Icy Cape, Alaska, which is also the western boundary of the Southern Beaufort Sea (SB) subpopulation (Amstrup et al. 1986; Amstrup and DeMaster 1988; Garner et al. 1990; Amstrup et al. 2004, 2005).

The first quantitative estimate of subpopulation size (2,937 95%CI = 1,552-5,944) was obtained from capture-recapture research in the U.S. portion of the subpopulation’s range (Regehr et al. 2018a). Population abundance was previously estimated to be between 2,000 and 5,000 animals based on the number of maternity dens observed on Wrangel and Herald islands and the Chukotkan coast, and the assumed proportion of females in the subpopulation (Belikov 1993). In recent years, sea ice has retreated farther north in the area occupied by the CS subpopulation resulting in more days in which the biologically productive waters of the continental shelf are ice-free (Durner et al. 2009; Rode et al. 2013). Sea-ice loss is expected to continue (Douglas 2010). Rode et al. (2013) documented stable or improving body condition and reproduction for polar bears captured in the U.S. between 1986-1994 and 2008-2011, a period during which substantial sea-ice loss occurred. This suggests some resiliency of the subpopulation to summer habitat loss. Autumn-based observations on Wrangel Island for the period 2004-2010, however, may have indicated declining cub production and maternity denning (Ovsyanikov 2012).

A quantitative harvest risk assessment has been completed using new estimates of abundance and vital rates (Regehr et al. 2018b). Estimates of illegal take of polar bears in Russia are based on village interviews conducted 2010-2012. The current take level in Russia appears to be significantly lower than in the 1990s although up-to-date and accurate estimates are lacking (Kochnev and Zdor 2016). Uncertainty in previous estimates of abundance and other subpopulation parameters (e.g., levels of human-caused removals) result in a designation of “Data deficient” for the long-term change in subpopulation size. The designation of “Likely stable” for short-term subpopulation trend is based on estimates of population growth rate using vital rates for the period 2008-2016 (Regehr et al. 2018b).

New studies have found that CS polar bears have increased land use during the summer, primarily on Wrangel Island and the Chukotkan peninsula in Russia (Rode et al. 2015). Further, Wilson et al. (2014, 2016) found that habitat selection preferences of polar bears on the sea ice in the Chukchi Sea have not changed over time despite declines in the availability of their preferred habitats. This suggests that CS bears are not adapting their habitat choices and that climate warming will continue to reduce the availability of preferred sea-ice habitat. The observed relationship between summer sea-ice availability and the duration of time and proportion of the CS subpopulation that comes to shore suggests that land use will increase as sea ice loss continues.

References

Reference list