Ringed seal (Pusa hispida) diet on the west coast of Spitsbergen, Svalbard, Norway

Abstract

The diet of 99 coastal-feeding ringed seals (Pusa hispida), collected in western Spitsbergen, Svalbard (Norway), was analysed via identification of hard-parts in the contents of their gastrointestinal tracts (GITs). The study animals where shot either in spring (n = 30; April-July) or autumn (n = 69; August-October) during four consecutive years (2014-2017). Thirty different prey types were identified in total, but most individual seals (55.6%) had consumed between 2-4 different prey types. Polar cod (Boreogadus saida) dominated in terms of relative biomass (Bi = 60.0%) and frequency of occurrence (FOi = 86.9%) in the diet, followed by pricklebacks (Stichaeidae; Bi = 23.4%; FOi = 79.8%). GITs collected in spring contained a lot of krill (Thysanoessa spp.) in adults of both sexes and in juvenile seals, but crustaceans were not important prey in terms of biomass. Redundancy analysis (RDA) revealed that year was the only significant predictor explaining variance in diet composition (F-ratio = 4.96, P = ≤ 0.005); i.e. blubber content and sex/age group were not significant. Atlantic herring (Clupea harengus) and blue whiting (Micromesistius poutassou) occurred in the diet in small quantities; these temperate fish species have not previously been documented in the ringed seals’ diet on Svalbard. Atlantic cod (Gadus morhua) had the highest Bi (9.2%) among Atlantic prey types. However, despite major changes in the last decade in the fish and zooplankton community in western Svalbard, and consumption of some few temperate prey types by ringed seals, the Arctic seal’s diet continues to be dominated by Arctic prey types, especially polar cod.