The Food of Fur Seals in the Eastern Bering Sea

Abstract

The development of commercial fisheries in the Aleutian area, particularly the catching of salmon in the open sea with drifting gill nets, has stimulated interest in the food of the Pribilof seal (Callorhinus ursinus) in the Bering Sea. Added interest results from the decline in the salmon runs in Bristol Bay. Fisheries investigators believe that at least part of the salmon migrating to rivers entering Bristol Bay pass through areas in the Bering Sea where fur seals feed intensively. No pelagic investigation of the food of fur seals while in the Bering Sea has been made since Alexander's in 1892. This was summarized by Lucas (1899) who wrote that Bering Sea during August and September the pollack (Theragra chalcogramma) forms the staple article of food, a squid (Gonatus amoenus) coming next in importance, while some salmon and a few species of small fish are also eaten. Lucas quotes Alexander in stating that material which has been found in the stomachs of seals taken in different parts of Bering Sea indicates that only a small percentage is composed of fish which inhabit deep water. It is only reasonable to suppose that when seals are in shallow water they feed on both bottom fish and those near the surface. Lucas footnoted the latter part of this statement, saying: There is, however, no evidence of this except in the rare presence of cottoids. . On the basis of stomachs collected from the killing fields, Kenyon (1956) has verified Alexander's statement. Most of the content of these stomachs (94 per cent) was composed of sand fish (Trichodon trichodon), which burrow in sand in relatively shallow water. The sturgeo -lik sea poacher (Agonus acipenserinus), second in importance, is also a bottom dweller. Fro 17 June to 20 July 1955, 204 fur seals were collected pelagically in the Bering Sea from Unimak Pa s and Unalaska to the Pribilof Islands. Most of the seals were collected by the authors by shooting with buckshot from the deck of a halibut schooner, the M/S Paragon. On the rare calm days two men worked from a dory powered with a 10horsepower utboard. In good weather this was as effective as the larger vessel, and fewer animals were lost when hunting with the dory. Throughout the period, seals were most abundant in or near Unimak Pass. Near the Pass were also Steller sealions (Eumetopias jubata), numerous humpback whales (Megaptera novaeangliae), and vast numbers of shearwaters (Puffinus spp.). It is reasonable to presume that the rich food supply attracted all thes forms. Pregnant females predominated among the seals collected, comprising 71 per cent of the total. Females without fetuses composed 16 per cent and males 13 per cent of the collection. Table 1 gives the food contained in the stomachs of 204 seals collected pelagically and of three others in the commercial kill at St. Paul Island where empty stomachs are the normal condition among the thousands we have examined. Capelin was the predominant food species in Unimak Pass and near the Aleutian Islands. It appears that concentrations of capelin are available for the seals during extensive portions of their northward migration. Scheffer (in Taylor, Fujinaga, and Wilke, 1955) found that capelin made up more