PROCEEDINGS OF THE CALIFORNIA ACADEMY OF SCIENCES / Liorary '' '" "'-"'<>i<on Volume 53, No. 2, pp. 11-21,1 fig., 8 tables. / / June 14, 2002 ^^N 2 2Q02 Status of Pinnipeds on Santa Catalina Island by Burney J. Le Boeuf Institute of Marine Sciences. Universit}' of California Santa Cruz, California 95064 email: leboeuf@cats. ucsc. edu The aim of this study was to assess the number and distribution of pinnipeds on Santa Catalina Island, the diet of California sea lions, Zalophus californianus, the incidence of pinniped strandings, and the significance of dead pinnipeds as a source of food and of organochlorine contamination for local bald eagles, Haliaeetus leucocephahis. Twenty-four censuses were conducted from February to November 2000. A maximum of 70 California sea lions was recorded in March; numbers decreased to at least half this size in summer and then increased again in the fall. The majority of sea lions were adult males (64%), no pups were observed, and most animals inhabited the southwest side of the island, 87% of them at Seal Rocks. Market squid, Loligo opalescens, was the dominant prey in February and March. The number of harbor seals, Phoca vitulina, peaked at 121 individu-als during the spring breeding season, and the seals were most numerous on the southwest side of the island. Only eight dead pinnipeds were observed during the study period, DDT residue levels in sea lion blubber were low, and bald eagles were never observed feeding on the carcasses. This suggests that dead pinnipeds are not an important source of food or con-tamination for the bald eagles of Santa Catalina Island. Santa Catalina Island is a haul-out site of minor importance for California sea lions, as reflected by low numbers observed and the absence of breeding; colony numbers of both pinnipeds are in equilibrium. The pinnipeds of Santa Catalina Island are of interest because of the island's location in the Southern California Bight (Fig. 1 ). First, the island is close to an ocean dumping site, and only 24 nau-tical miles from the sewage outfall on the Palos Verdes Shelf in Los Angeles where large quantities of DDT residues were discharged between 1948 and 1970 and still remain on the ocean floor (MacGregor 1974; Chartrand et al. 1985). Pinnipeds, especially the California sea lion, Zalophus californianus, accumulate high organochlorine pesticide levels from their diet (Le Boeuf and Bonnell 1971; DeLong et al. 1973; Buhler et al. 1975; Gilmartin et al. 1976; Lieberg-Clark et al. 1995). Pinnipeds on Santa Catalina Island might exhibit greater than normal contaminant loads, compared with animals from other islands in the Southern California Bight, if their prey are contaminated from feeding near the dumpsites. If so, the dead bodies of these pinnipeds might be a source of contamina-tion for scavenging birds (Garcelon 1 994a). Second, due to the island's close proximity to a large met-ropolitan area, it supports the largest year-round resident population of humans of all the islands in southern California, a high influx of transient tourists from spring through fall, and attendant large-scale recreational boating activities. This might disturb the pinnipeds, limiting their number, af-fecting their temporal and spatial use of the island, and reducing their reproduction. The aim of this pa-per is to address the validity of this logic by presenting data on number, distribution, mortality and diet of the pinnipeds on this island. 11
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