Opportunistic counts of Northern sea lions (Eumetopias jubatus) in Glacier Bay National Park and Preserve

Mathews, E

The northern sea lion (Eumetopias jubatus) population has declined severely during the last three decades, particularly in the eastern and central Aleutian Islands and the central and western Gulf of Alaska (Merrick 1987; Loughlin et al. 1992). At 77 trend sites (haulouts and rookeries which have been censused during all of the major surveys), sea lion numbers have declined by 78% since the late 1950s (Merrick 1991). In 1990, the northern sea lion was listed as a threatened species under the Endangered Species Act. Declines have been documented in all regions of Alaska except southeast Alaska (Loughlin et al. 1992). The northern (Steller) sea lion occurs in the North Pacific from Japan through the Aleutian Islands and Bering Sea, throughout southeast Alaska and down to southern California. In 1989 an extensive survey was conducted by the National Marine Fisheries Service to assess the status of sea lions throughout their range (Loughlin et al. 1992). The number of non-pup sea lions estimated for southeast Alaska in 1989 was 12,303, about 14% of the world population. In this report I summarize recent opportunistic counts of sea lions in park waters and document that over 1,100 sea lions -- approximately 9% of the estimate for southeast Alaska -- use haulouts in Glacier Bay and along the park's outer coast. During three aerial surveys for harbor seals in 1992 and 1993 (Mathews 1992 and in prep.), I photographed northern sea lions hauled out on Graves Rocks, near Cape Spencer (136º40'W, 58º15'N) and on Lituya rocks, east of the mouth of Lituya Bay (137º 30'W, 48º30'N). In addition to the counts from aerial photographs, opportunistic visual counts of sea lions at a haulout along the northern shore of South Marble Island (136ºo5'W, 58º37'N) in Glacier Bay have been made from boats by several observers. In this report I summarize the results of counts from the aerial photographs of the two haulouts along the outer coast and from some of the opportunistic counts of sea lions at South Marble Island.