Fatty acid composition of the adipose tissue of polar bears and of their prey: ringed seals, bearded seals and harp seals

Polar bears Ursus maritimus are predators of phocid seals, but they also forage opportunistically on a variety of other species. In the Barents Sea-Svalbard area, their diet is thought to consist almost exclusively of ringed seals Phoca hispida, bearded seals Erignathus barbatus and harp seals P. groenlandica. When a seal is killed, polar bears preferentially consume the blubber. The fatty acid (FA) compositions of the outer, middle and inner adipose layer of 18 polar bears were compared to each other and also with the FA composition of the blubber of their prey, represented by 10 ringed seals, 10 harp seals and 9 bearded seals. The composition of the FAs in the inner layer of the bear adipose tissue differed from the composition of the outer layer, and was also distinctly different from the composition of the blubber from the prey. Fifteen of the 28 FAs analysed were found in lower relative amounts in the polar bears than in any of the 3 seal species. Eight of the FAs were found in higher relative amounts in polar bears when compared to the 3 prey species. Only 5 of the FAs in polar bears were within the range of relative values found in the prey. This strongly suggests that polar bear adipose tissue has a unique FA composition that is not a straightforward mixture of what they consume, but rather is the result of selective processes prior to and during deposition of lipids in the tissue.