The body conditions of polar bear (Ursus maritimus) populations around the Norwegian island of Svalbard have improved despite sea ice losses, according to research published in Scientific Reports. The findings differ from previously published observations of polar bear population declines coinciding with sea ice loss across the Arctic.
Previous research has recorded temperature increases in the Barents Sea region surrounding Svalbard of up to two degrees Celsius per decade since 1980. However, following a 2004 census, the Barents Sea polar bear population numbered approximately 2,650 individuals and until recently appeared not to shrink in size, although the reasons for this have been unclear.
Jon Aars and colleagues investigated the potential causes of the stability of the Svalbard populations using data from 1,188 body measurement records of 770 adult polar bears taken on Svalbard between 1992 and 2019. They compared changes in the bears' body composition index (BCI), an indicator of fat reserves and body condition, with the number of ice-free days in the Barents Sea region across the 27-year period. The authors found that although the number of ice-free days increased by approximately 100 over this period — at a rate of about four days per year — the mean BCI of the adult polar bears sampled increased following the year 2000. This indicates that fat reserves increased as sea ice levels decreased.
The authors suggest that improvements in the body conditions of Svalbard polar bears could be attributed to the recovery of populations of land-based prey sources that were previously over-exploited by humans, such as reindeer (Rangifer tarandus) and walrus (Odobenus rosmarus). They also propose that sea ice loss may lead to prey animals such as ringed seals (Pusa hispida) concentrating across smaller areas of sea ice and that this may increase the efficiency of polar bear hunting. The authors speculate that further reductions in sea ice may negatively affect the Svalbard populations by increasing the distances they need to travel to access hunting grounds, as this has already been observed in other polar bear populations. They conclude that more research is needed to understand how different polar bear populations will adapt to a warming Arctic in the future.
