Shark-inflicted lesions on California sea lions
Shark-inflicted lesions on California sea lions (Zalophus californianus) at
San Miguel Island, California: A new phenomenon
Jeffrey D. Harris, Sharon R. Melin, and Robert L. DeLong
Shark-inflicted lesions on California sea lions (Zalophus californianus) were observed in unprecedented numbers on San Miguel Island (SMI), California,from February to September 2011. Prior to this time period (1972-2010), there was little observational evidence of shark predation on SMI sea lions.We documented 134 living animals with lesions including 95 adult females, 36 juveniles and 3 adult males. Lesion condition (fresh, healing, scarred) was used to assess the peak period of shark predation; 88% of all freshly inflicted lesions occurred in June and July. Based on distinct lesion patterns, 40 of the lesions could be assigned to the shortfin mako shark (Isurus oxyrinchus) and 13 to sub-adult white sharks (Carcharodon carcharias). Shark predation on California sea lions at SMI is ecologically important and may signify the return of apex predators following the cessation the California drift gillnet fishery (1981-1991) in the Southern California Bight. Adult female and juvenile survival drives California sea lion population growth and if predation persists on these age classes it may emerge as a key factor in population dynamics.