Survey of death causes in northern fur seal pups on bering island ― on the basis of pathological changes

Thirty-two northern fur seal (Callorhinus ursinus) pups were examined pathologically. These died within two months of age and were collected in the Northwest Rookery of Bering island in the Kommandorski Islands, Russia, between July 6 and 23, 1995. The main causes of death were as follows：uncinariosis in 20 pups (63%), trauma in 5 pups (16%), emaciation (starvation and malabsorption) in 4 pups (13%), and pneumonia in 3 pups (9%). It was suggested that the higher mortality of pups on this island was mostly due to hookworm infestation, while emaciation was a common finding. Uncinariosis in fur seal pups has seldom been seen in other areas of the world. The gross and histological findings suggested that severe infestation of hookworms caused continuous hemorrhaging from the small intestine, resulting in severe chronic systemic anemia and death. The animals showed extramedullary hemopoiesis in varying degrees, which was marked (predominantly in myeloblastic cells) in pups with severe hookworm infestation.