Estimated prey consumption by harp seals (phoca groenlandica), hooded seals (cystophora cristata), grey seals (halichoerus grypus) and harbour seals (phoca vitulina) in Atlantic Canada

Abstract

Consumption of prey by harp (Phoca groenlandica), hooded (Cyslophora cristaia), grey (Halichoerus grypus), and harbour (Phoca vitulina) seals in Atlantic Canada was estimated for the period 1990-96 by synthesizing and integrating information on individual energy requirements, population size, distribution and diet composition. Total annual consumption by these four species increased from 3.1 million to 4.0 million tons over the seven-year period. Seventy-seven percent (by weight) of the total prey consumption consisted of fish, of which capelin and sand lance were the dominant species accounting for 49% (by weight) of the total fish consumed. The majority (74%) of total prey consumption occurred off southern Labrador and Newfoundland (Div. 2J and 3KL), followed by the northern Gulf of St Lawrence (Div. 4RS) (18%), and the eastern Scotian Shelf (Div. 4Vs\V) (4%). Harp seals were the most important predator, accounting for 82% of total consumption, followed by hooded seals (10% of total prey consumption), grey seals (7.8%), and harbour seals (0.2%). Regional differences existed in prédation impacts of the four pinnipeds; harp seals were most important in Div. 2J and 3KL and in Div. 4RS, hooded seals were most important in Div. 2J and 3KL and Div. 3M (Flemish Cap), while grey seal prédation predominated in the southern Gulf of St. Lawrence (Div. 4T) and on the Scotian Shelf (Div. 4VsW). Of the 3.1 million tons of fish consumed by the four species of seals in 1996, only about 20% accounted for commercial species such as Greenland halibut (7%), Atlantic cod (6%), redfish (4%), and Atlantic herring (3%). Most of the consumption of these commercial species consisted of juveniles.