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Comparative feeding habits of the fur seal (Callorhinus ursinus), sea lion (Eumetopias jubata) and harbour seal (Phoca vitulina) on the British Columbia coast. Spalding, David Joseph Reede

Abstract

Feeding habits of fur seals (Callhorinus ursinus), sea lions (Eumetopias jubata) and harbour seals (Phoca vitulina) have been examined along the British Columbia coast. Collections were made out to 35 miles from shore. All pertinent published and unpublished data have been combined with the object of assessing the effect of pinniped predation upon commercially valuable fish stocks. A total of 126 harbour seal stomachs, 2,113 fur seal stomachs and 393 sea lion stomachs were available. Comparative anatomy of the digestive tract was examined and notable differences were found in the relatively longer digestive tract and late eruption of permanent teeth in the sea lion. Published data indicate that fur seals, sea lions, and harbour seals eat an amount of food equal to 6%of their body weight per day with a range of 2% to 11%. All samples were grouped as to season and area of collection and comparative seasonal feeding habits were discussed. The effect of the reproductive period upon feeding habits was examined: there is little evidence regarding fur seal feeding habits on the rookeries except for conflicting observations made on harem bulls; the majority of the sea lion rookery population fasts for a few days only, during pupping; harbour seals on the Skeena River appear to fast for at least part of June. There is no evidence of interspecific competition between the three species studied on the British Columbia coast. Sea lions and harbour seals each year eat an estimated amount equivalent to 1.6% of the annual commercial salmon catch and 2.7% of the annual commercial herring catch. Predation at this level is believed to be of negligible importance in the reduction of existing salmon and herring stocks. Insufficient data from waters greater than 35 miles from shore precludes an assessment of fur seal predation upon ocean salmon. Further offshore collections should be made.

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