Offshore diet of grey seals Halichoerus grypus near Sable Island, Canada

Abstract

Many pinnipeds forage considerable distances from mainland haul-out sites for much of the year, yet little is known about the composition of their offshore diets. This may result in an incomplete and potentially biased view of the diet of wide-ranging species such as the grey seal Halichoerus grypus. On the Scotian Shelf, offshore fish assemblages differ from those nearer the coastal mainland sites and thus we expected that grey seal diets would also differ. We studied the composition of grey seal diets at Sable Island, an offshore site 160 km east of Nova Scotia, Canada. Otoliths, squid beaks and other hard parts, representing more than 24 types of prey, were recovered from 365 of 393 grey seal faeces collected between July 1991 and January 1993. Despite the large number of taxa found, 3 preysand lance Ammodytes dubius (69.2%), Atlantic cod Gadus morhua (15.5%) and flatfishes (Pleuronectiformes, 10.7 %)accounted for 95.4 % of the estimated wet weight food consumed by grey seals. Despite within-year vanation in the species composition of grey seal diets, sand lance was the most important food in all months sampled. Comparisons of prey species abundance in research trawl surveys to that in grey seal diets indicated that more abundant and more widely distributed species accounted for most of the prey eaten.