Integrated study of benthic foraging resources for Atlantic walrus (Odobenus rosmarus rosmarus) in the Pechora Sea, south‐eastern Barents Sea

Abstract

The Atlantic walrus, Odobenus rosmarus rosmarus, forms a herd of nearly 4,000 heads in the Pechora Sea (south‐eastern Barents Sea). The Near Threatened status of O. rosmarus rosmarus and the relative isolation of the Pechora Sea population, as well as the potential impacts of human activities in the area, make it important to characterize key habitats, including feeding grounds, in order to protect the species. The aim of the present study was to integrate multiple sources of environmental and biological data collected by satellite telemetry, remotely operated vehicle (ROV), and benthic grab sampling to examine the distribution and diversity of benthic foraging resources used by walrus in the Pechora Sea. Analysis of satellite telemetry data from seven males tagged on Vaigach Island helped to identify areas of high use by walruses near haulout sites on Matveev and Vaigach islands, and in between. Field data were collected from those feeding grounds in July 2016 using ROV video recordings and bottom grab sampling. Analysis of 19 grab stations revealed a heterogeneous macrobenthic community of 133 taxa with a mean biomass of 147.11 ± 7.35 g/m2. Bivalve molluscs, particularly Astarte borealis, Astarte montagui, and Ciliatocardium ciliatum, dominated the overall macrobenthic biomass, making up two‐thirds of the total. Analysis of 16 ROV video transects showed high occurrences of mobile benthic decapods (3.03 ± 2.74 ind./min) and provided the first direct evidence that areas actively used by walrus in the Pechora Sea overlap with the distribution of the non‐native omnivorous snow crab, Chionoecetes opilio. Integrating multiple data sources provides an early foundation for the kinds of ecosystem‐based approaches needed to improve Pechora Sea resource management and to underpin Russia’s nascent marine spatial planning initiatives. Factors that need to be considered in marine spatial planning include impacts on benthic feeding grounds from offshore oil and gas development and the spread of the snow crab.

Trophic niches of benthic crustaceans in the Pechora Sea suggest that the invasive snow crab Chionoecetes opilio could be an important competitor

“…The online version of this article (https ://doi.org/10.1007/s0030 0-020-02775 -3) contains supplementary material, which is available to authorized users. due to their importance as feeding grounds for seabirds and marine mammals (Spiridonov et al 2017;Denisenko et al 2019a;Gebruk et al 2020). However, rapid increases in human activities such as oil and gas extraction, shipping, tourism, combined with climate change, introduction of invasive species and the release of contaminants are predicted to have a cumulative impact on the unique marine ecosystems of the Pechora Sea (Sukhotin et al 2019;Semenova et al 2019).…”

“…Pink dashing shows distribution of the snow crab in the research area (Lorentzen et al 2018); purple dashing marks feeding grounds of Atlantic walruses (Semenova et al 2019;Gebruk et al 2020); green dashing corresponds to the key moulting and migrating areas of sea ducks (Sukhotin et al 2008). b Detailed map of the sampling area: trawling sites are shown with red pins; circles of different colours represent biomass of dominant species in macrobenthic communities (Gebruk et al 2020) as the Pianka's measure, MacArthur and Levins' measure, Morista's measure and others (Kerbs et al 2017). Similarly, the composition of stable isotopes of carbon and nitrogen in animal tissues is used in feeding ecology as an emergent property of dietary niches and habitat use (Post 2007;Flaherty and Ben-David 2010).…”

“…Average biomass of macrobenthos in the Pechora Sea ranges from 1.5 to 536 g wet weight per m 2 (Denisenko et al 2003). The shallows of Pechora Bay are characterised by particularly low biomass (Gebruk et al 2019;Denisenko et al 2019b), whilst the north-western parts near the Novaya Zemlya and Vaygach Islands have the highest values of biomass of macrobenthic invertebrates in the Pechora Sea with largest contributions formed by bivalve molluscs Astarte borealis, Ciliatocardium ciliatum, Serripes groenlandicus, Nicania montagui and Macoma calcarea (Denisenko et al 2019a;Gebruk et al 2020). The presence of C. opilio and predation on benthic invertebrates may have an impact on the structure of these macrobenthic communities in the Pechora Sea, and may also go on to affect the availability of benthic feeding resources for seabirds (i.e.…”

“…The presence of C. opilio and predation on benthic invertebrates may have an impact on the structure of these macrobenthic communities in the Pechora Sea, and may also go on to affect the availability of benthic feeding resources for seabirds (i.e. common eiders and other sea ducks) and marine mammals that forage on the benthos here including Atlantic walrus (Odobenus rosmarus; Gebruk et al 2020)…”

“…The study area lies within the important feeding grounds of Atlantic walruses (Semenova et al 2019;Denisenko et al 2019a;Gebruk et al 2020), and marine duck species, including kind eiders, black and velvet scoters (Sukhotin et al 2008). According to previous benthic surveys, macrobenthos in the area is formed by diverse communities of 133 species of invertebrates (Gebruk et al 2020). Macrobenthic biomass is predominately formed by bivalve astartid molluscs (with the biggest contributions from Astarte borealis, Astarte montagui and Ciliatocardium ciliatum), but it varies greatly ranging from 32 g m −2 (site 4 N) to 500 g m −2 (site 9 N) (Gebruk et al 2020) (Table 1, Fig.…”