Predation by sea lions on northern fur seal neonates

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Abstract
Since 1967 northern sea lions, Eumetopias jubatus, were seen killing and eating neonates (under 5 mo. of age) of the northern fur seal, Callorhinus ursinus, in the waters near St. George Island, Alaska [USA]. Data collected in 1974 and 1975 represent the 1st successful attempt to quantify the predation rate of 1 pinniped species on another. All kills are made near shore by juvenile males hunting singly although 2 animals sometimes feed on the same carcass. Kills 1st occur when neonates enter the sea in Aug. and continue until Nov. each year. The kill rate is greatest from 0800-1000, and from 1500-1700 h, coinciding with the hours of greatest sea lion movements to and from rest sites on the island. The kill rate is greatest at locations where sea lions come ashore in greatest numbers, despite the fact that prey concentration is much greater at other sites. Sea lions are estimated to have killed from 2700-5400 fur seal neonates in 1975, or 3.4-6.8% of the neonates alive at that time. Fur seals are supplementary to the sea lion diet rather than primary. The number taken by sea lions constitutes a relatively small fraction of fur seal mortality from birth to age 2 yr.