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 prey -sand 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.
We studied the composition of harbour seal (Phoca vitulina) diets in two areas, the lower Bay of Fundy and along the northeastern coast of Nova Scotia, that differ in prey species diversity, bottom type, and physical oceanography. Prey remains were found in 250 of 470 harbour seal stomachs collected mainly from May to September between 1988 and 1992. Although 23 taxa were identified, four species, Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), pollock (Pollachius virens), and short-finned squid (Illex illecebrosus), accounted for 84% of the estimated biomass of prey consumed in the two areas combined. Species, such as herring and squid, that dominated the diets in both habitats, also tended to be abundant in both habitats during the summer. Atlantic cod was the principal gadoid in the Bay of Fundy, whereas pollock was most important along the Atlantic coast. Differences in prey distribution and abundance appeared to account for differences in the contribution of the alewife (Alosa pseudoharengus), winter flounder (Pseudopleuronectes americanus), hake (Urophycis spp.), and capelin (Mallotus villosus) in the diet. Pronounced interannual variation in the species composition of diets was evident in both habitats. This variation was associated with broad-scale changes in prey abundance in some cases (e.g., squid and capelin) but not in others (e.g., Atlantic cod and pollock).
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.