Ringed seal (Pusa hispida) diet on the west coast of Spitsbergen, Svalbard, Norway: during a time of ecosystem change

O Bengtsson,U Lindström,K M Kovacs,C Lydersen

doi:10.1007/s00300-020-02684-5

O Bengtsson, U Lindström + Show 2 more

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https://doi.org/10.1007/s00300-020-02684-5

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Abstract

Global warming is causing Atlantification of water masses and concomitant changes in food webs in the Barents Sea region. To determine whether changes that have been documented at lower trophic levels are impacting the diet of ringed seals (Pusa hispida) gastrointestinal tracts (GITs) from 99 coastal-feeding ringed seals, collected in western Spitsbergen, Svalbard, were analysed via identification of hard-parts. The study animals were shot in spring (n = 30; April–July) or autumn (n = 69; August–October) during four consecutive years (2014–2017). Thirty different prey types were identified, but most seals (55.6%) had consumed between 2 and 4 different types of prey. Polar cod (Boreogadus saida) dominated the diet of the ringed seals in terms of relative biomass (Bi = 60.0%) and frequency of occurrence (FOi = 86.9%), followed by pricklebacks (Stichaeidae; Bi = 23.4%; FOi = 79.8%). Redundancy analysis (RDA) revealed that year was the only significant predictor explaining variance in autumn diet composition (RDA, F3 = 4.96, AIC = − 76.49, p ≤ 0.0050; blubber content and maturity/sex group were not significant). Blue whiting (Micromesistius poutassou) occurred in the diet in small quantities; this Atlantic fish species has not previously been documented in the ringed seals’ diet. 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 a few Atlantic prey types, the ringed seals’ diet in Svalbard continues to be dominated by Arctic prey, especially polar cod.

Highlights

The ringed seal (Pusa hispida hispida) is an important species in Arctic food webs, both as a predator of a variety of fish and invertebrate species (McLaren 1958; Labansen et al 2007; Crawford et al 2015) and as a primary prey species for polar bears (Ursus maritimus; Stirling and Øritsland 1995; Iversen et al 2013) and coastal people in the Arctic (Teilmann and Kapel 1998)
Otoliths were found in 91.9% of the gastrointestinal tracts (GITs) and 49.5% contained crustaceans (Table 2)
The results of the current study suggest that the spring diet of ringed seals in this region might have become somewhat more varied following the environmental changes during the last decades

Summary

Introduction

The ringed seal (Pusa hispida hispida) is an important species in Arctic food webs, both as a predator of a variety of fish and invertebrate species (McLaren 1958; Labansen et al 2007; Crawford et al 2015) and as a primary prey species for polar bears (Ursus maritimus; Stirling and Øritsland 1995; Iversen et al 2013) and coastal people in the Arctic (Teilmann and Kapel 1998). Svalbard ringed seals remain associated with ice, travelling offshore, to areas along the ice edge (Freitas et al 2008; Hamilton et al 2015; Lone et al 2019), or remaining in the fjords, where they use glacier ice as resting platforms and feed on concentrations of prey at up-welling areas at the front of tidewater glaciers (Hartley and Fisher 1936; Freitas et al 2008; Lydersen et al 2014; Hamilton et al 2016, 2019b)

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