Two Shark Species Involved in Predation on Seals at Sable Island, Nova Scotia, Canada

Abstract

Between 1993 and 2001, 4906 seal corpses bearing wounds likely inflicted by sharks were examined on Sable Island, Canada. Five seal species were involved: grey (Halichoerus grypus), harp (Pagophilus groenlandica), harbour (Phoca vitulina), hooded (Cystophora cristata), and ringed (Phoca hispida) seals. Flesh wounds on seal corpses indicated that two or more shark species prey on seals in waters around Sable Island. Wounds were categorized as either slash or corkscrew, with different predators identified for each type. Wound patterns, tooth fragments, and marks on bones indicated that white sharks (Carcharodon carcharias) were involved in the slash wounds, which comprised a small proportion of attacks. Ninety-eight percent of seal corpses, however, bore the corkscrew wounds that could not be attributed to shark species identified in attacks on pinnipeds in other regions and these wounds are previously unreported in the literature. Circumstantial evidence indicates that attacks by Greenland sharks (Somniosus microcephalus) were responsible for the clean-edged encircling corkscrew wounds seen on seal corpses washed ashore on Sable Island.