Seasonal and interannual variability in grey seal diets on Sable Island, eastern Scotian Shelf

Abstract

We studied seasonal and interannual variability in the diet of grey seals (Halichoerus grypus) using faecal samples collected from Sable Island, Nova Scotia between 1991 and 1998. More than 28,000 prey from at least 28 taxa were identified from 1,245 faecal samples collect mainly in spring, fall and winter. Sand lance (Ammodytes dubius) dominated the diet in all season and years, but the importance of this and other species varied over time. There was also evidence of seasonal and interannual variation in the size of prey consumed both within and among species. We compared diet composition with estimates of prey numbers and biomass from annual research trawl surveys conducted in March and July. Species-specific numerical corrections were applied to otolith counts to account for the complete digestion of otoliths, and fish catchability correction factors applied to trawl survey catches to account for trawl selectivity. Based on an odds ratio index of prey selectivity, grey seals positively selected sand lance in both seasons. Other species were either relatively avoided or eaten roughly in proportion to their estimated abundance.

Continued Decline of an Atlantic Cod Population: How Important Is Gray Seal Predation?

“…account for most of their diet (Bowen et al 2006). There is also some evidence that gray seals do not positively select for cod relative to their abundance (Bowen and Harrison 2006), which has also been observed in harp seals (Lawson et al 1998).…”

Seal–cod interactions on the Eastern Scotian Shelf: Reconsideration of modelling assumptions

“…The diet composition information for seals in the northwest Atlantic covers the time period from 1950 (Fisher and Mackenzie, 1955) to 2010 Bowen and Harrison, 2007;Bowen et al, 2011;Stenson et al, 2010). For the northeast Atlantic, there are published observations from 1967 (Rae, 1968(Rae, , 1973 to 2002 (Hammond and Harris, 2006;Hammond and Grellier, 2006).…”

Fueling phocids: Divergent exploitation of primary energy sources and parallel ontogenetic diet switches among three species of subarctic seals

“…We already have a good idea of trophic levels occupied by these seals given other quantitative descriptions of diet composition ( e.g., Hammill and Stenson , Haug et al . , Bowen and Harrison ). All three species consume a mix of invertebrates and fishes, making them to varying degrees, secondary and tertiary consumers.…”

“…Gray seals are sex‐dimorphic, generalist predators consuming a mixture of both demersal and pelagic fishes, with males being about 50% heavier than females (Beck et al . , Bowen and Harrison ). There is evidence of dietary niche segregation in gray seals with an increasing reliance on demersal prey in larger and older individuals and from females to males (Beck et al .…”

“…Gray seals (Halichoerus grypus) are a wide-ranging and abundant species inhabiting the continental shelf of the Northwest Atlantic and diving to depths generally <100 m (Beck et al 2003, Austin et al 2004, Breed et al 2006. Gray seals are sex-dimorphic, generalist predators consuming a mixture of both demersal and pelagic fishes, with males being about 50% heavier than females (Beck et al 2007, Bowen andHarrison 2007). There is evidence of dietary niche segregation in gray seals with an increasing reliance on demersal prey in larger and older individuals and from females to males (Beck et al 2007).…”