Causes of Live Strandings of Northern Elephant Seals (Mirounga angustirostris) and Pacific Harbor Seals (Phoca vitulina) Along the Central California Coast, 1992-2001

Between January 1992 and December 2001 a total of 1,277 northern elephant seals (Mirounga angustirostris) and 940 Pacific harbor seals (Phoca vitulina) were stranded live along the central California coast. By examining medical records for each of the stranded seals, the primary cause of stranding and the secondary factors contributing to stranding were determined. The majority (88.3%) of animals were young born that year. The most common causes of live strandings for elephant seals included malnutrition (56.6%), Otostrongylus circumlitus infection (12.1%), and northern elephant seal skin disease (9.8%). The most common causes of strandings for harbor seals were malnutrition (51.8%), respiratory disease (9.6%), and trauma (8.0%). Common secondary factors for strandings for both elephant and harbor seals included human interaction, trauma, and ocular disease. For both species of phocid, the highest prevalence of O. circumlitus infection occurred in 1992 and 1993, years of a moderate El Niño-Southern Oscillation event. Phocine herpesvirus-1 infection was a common primary and secondary factor in harbor seal strandings, and the highest prevalence occurred between 1994 and 1998. Human interference in stranding events increased in the past ten years and is most commonly reported on beaches near heavily populated areas.