New survey estimates 10x as many polar bears in Russian section of Chukchi Sea as in USA portion

A joint US/Russian aerial survey has estimated that a minimum of 3,435 polar bears (but possibly as many as 5,444) likely inhabited the Chukchi Sea in 2016, quite a bit more than a previous study that estimated a population size of 2,937 the same year (which used data from one small US area extrapolated to the entire region).

The study, done by fixed-wing aircraft in April and May 2016 (Conn et al. 2021), estimated 3095 bears in the Russian portion of the Chukchi Sea compared to 340 in the US portion. That’s almost 10 times as many Russian bears as US bears in the Chukchi Sea, a statistic we’ve never had before now. The number estimated for the US portion in this study was almost 3 times as many as was estimated for the previous Regehr and colleagues study (340 vs. 126)(Regehr et al. 2018). Based on this latest data, the density of bears was said to be about half (~0.001 bears/km2) the density calculated from 1987 aerial survey data (0.002 bears/km2) but whether these figures are truly comparable remains to be determined.

This study required rather more models and associated assumptions than usual to come up with its population estimates. That’s primarily because they were based on sightings of only 8 bears or groups of bears in the US and 49 bears or groups of bears in Russia (‘groups’ were mothers and cubs) and surveys were limited primarily due to foggy weather and changing sea ice conditions. Small sample sizes are always problematic in this kind of research. However, because complex models and small sample sizes (only ~43 bears per year) also plagued the Regehr et al. study and that did not prevent it from being taken seriously by the polar bear conservation community (IUCN PBSG 2019), I fully expect this one to be considered a valid new population estimate for the Chukchi Sea.

While admitting that using fixed aircraft and heat-detecting technology for the first time in this count presented a number of challenges, the authors propose the method could yield better results once the kinks are sorted out.

The video of flight paths during the study (below) was provided by the authors, where the hatched area is ice:

Conn, P.B., Chernook, V.I., Moreland, E.E., Trukhanova, I.S., Regehr, E.V., Vasiliev, A.N., Wilson, R.R., Belikov, S.E. and Boveng, P.L. 2021. Aerial survey estimates of polar bears and their tracks in the Chukchi Sea. PLoS ONE 16(5): e0251130. https://doi.org/10.1371/journal.pone.0251130 OPEN ACCESS

video: https://doi.org/10.1371/journal.pone.0251130.s003

IUCN Polar Bear Specialist Group Status Report 2019. Status Report on the World’s Polar Bear Subpopulations. July, 2019 (posted September 2019). pdf here.

Regehr, E.V., Hostetter, N.J., Wilson, R.R., Rode, K.D., St. Martin, M., Converse, S.J. 2018. Integrated population modeling provides the first empirical estimates of vital rates and abundance for polar bears in the Chukchi Sea. Scientific Reports 8 (1) DOI: 10.1038/s41598-018-34824-7  https://www.nature.com/articles/s41598-018-34824-7

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