PRELIMINARY INVESTIGATIONS OF SHARK PREDATION ON CAPE FUR SEALS ARCTOCEPHALUS PUSILLUS PUSILLUS FROM THE EASTERN CAPE COAST OF SOUTH AFRICA

Abstract

SUMMARY Shark predation on Cape fur seals, Arctocephalus pusillus pusillus, from the Eastern Cape coast of South Africa was investigated. Observations were made on an opportunistic basis over a five year period from 1991 to 1996. Evidence of shark predation was obtained from: (1) incidental observations of shark attacks on live Cape fur seals, and (2) counts of shark bite wounds on the bodies of live and dead seals. In Eastern Cape waters, potential shark predators include the white, Carcharodon carcharias; broadnose sevengill, Notorynchus cepedianus; bluntnose sixgill, Hexanchus griseus; shortfin mako, Isurus oxyrinchus; bull, Carcharhinus leucas; tiger, Galeocerdo cuvier; and dusky, Carcharhinus obscurus. Only the white and broadnose sevengill shark have been observed actively feeding on Cape fur seals. Shark bitten seals (n = 33) were observed throughout the year, with coastal records peaking in the autumn/winter period. Adult animals were observed with shark bite wounds more often than young. Wounds were usually located on the lower body, suggesting that attacks were made from behind. Fresh shark bite wounds were found on a minimum of 3.4% of seals found stranded on local beaches, and 0.3% of seals observed at the Black Rocks colony during the breeding season. Although predatory encounters appear to be common, long term studies are required before we can fully assess the extent of shark predation along the Eastern Cape coast. These records are the only known examples of shark inflicted injuries on southern fur seals Arctocephalus spp. south of 10°S.