because of its isolation and the high productivity of the bering sea and the pacific continental shelf, the reserve is marked by a great diversity of animal life. it is a refuge for over a million seabirds, several hundred thousand northern fur seals, several thousand steller's sea lions, common seals, and spotted seals, a healthy population of sea otter, some 21 whale species, two rare endemic subspecies of arctic fox, and many endangered or threatened migratory birds, such as the whooper swan, steller's eider, and steller's sea eagle. furthermore, it is biogeographically unique stepping stone between asian and north american flora and fauna.