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.
KEY WORDS: Shark Seal, Sable Island, Greenland shark, Somniosus
microcephalus predation