Variation in the diet of beluga whales in response to changes in prey availability: insights on changes in the Beaufort Sea ecosystem

Abstract

The eastern Beaufort Sea (EBS) beluga whale Delphinapterus leucas population has experienced a 20 yr decline in inferred growth rates of individuals, which is hypothesized to have resulted from changes in prey availability. We used fatty acid signatures and stable isotope ratios to reconstruct the proportional contributions of 14 prey species to the diets of 178 beluga whales from 2011 to 2014. Prey estimates using quantitative fatty acid signature analysis suggest that EBS beluga whales primarily consume Arctic cod Boreogadus saida, a species highly sensitive to climate change. Prey estimates varied with year and sex and size class of the whales, with large males consuming the highest proportions of Arctic cod, and females consuming the highest proportions of capelin Mallotus villosus. Estimated proportional contributions of Arctic cod to beluga diet decreased from 2011 to 2014, coinciding with an increase in capelin. Belugas consumed the highest proportions of capelin and the lowest proportions of cod in 2014, the same year in which body condition indices were lowest in the whales. We hypothesize that changing conditions in the Beaufort Sea ecosystem may result in a decreased consumption of Arctic cod by belugas and increased consumption of capelin, which may result in a decline in condition. This may predominately affect females and juveniles since they consume the highest proportions of capelin; however, long-term monitoring is needed for confirmation. Understanding inter-annual variation in prey, and the longer-term nutritional implications of shifting from an Arctic cod- to a capelin-dominated diet should be a priority for monitoring EBS predators.

Circumpolar phylogeography and demographic history of beluga whales reflect past climatic fluctuations

“…The potential response of belugas to near‐future climate change may be a population‐specific combination of site fidelity and spatial flexibility, interacting with local or regional factors, such as prey availability, predation, and anthropogenic activities, which are all predicted to rapidly change as a consequence of climate change, and negatively impact beluga populations (Choy et al, 2020; Ferguson et al, 2010; Reeves et al, 2014; Small et al, 2017; Smith et al, 1992).…”

Climate change impacts on sea-ice ecosystems and associated ecosystem services

“…In both polar regions, strong direct reliance on sea-ice derived organic matter has been shown in all ecosystem compartments, that is, sympagic (Søreide et al, 2006;Budge et al, 2008;Kohlbach et al, 2016;Kohlbach et al, 2017b), pelagic (Wang et al, 2015;Jia et al, 2016;Kohlbach et al, 2018;Schmidt et al, 2018;Kohlbach et al, 2019b), andbenthic (McMahon et al, 2006;Norkko et al, 2007;Søreide et al, 2013;Wing et al, 2018;Kohlbach et al, 2019a;Michel et al, 2019). Trophic linkages are not limited to primary consumers but extend to higher trophic levels (Bluhm and Gradinger, 2008;Kohlbach et al, 2017a;Brown et al, 2018;Choy et al, 2020) as indicated by the selection of icedependent species shown in Figure 4. In the Arctic Ocean, the under-ice fauna transfers the bulk of sympagic carbon to the pelagic system, and the contribution of the sea-ice meiofauna is very small (Ehrlich et al, 2021).…”

“…Arctic cod (Boreogadus saida) is a critical carbon source for seabirds, fish, and marine mammals in high Arctic ecosystems (Bradstreet et al, 1986;Coad and Reist, 2004;Choy et al, 2020), many of which are key subsistence species harvested by northern communities (e.g., Inuvialuit communities; Harwood et al, 2015). Arctic cod has been reported as the most abundant fish species across a range of habitats (Rand and Logerwell, 2010;Hop and Gjøsaeter, 2013;Melnikov and Chernova, 2013;Walkusz et al, 2013;David et al, 2016;Majewski et al, 2017;Forster et al, 2020;Marsh et al, 2020).…”

“…However, the beluga-sea ice association is complex, showing variability across populations, as well as preference of ice concentration depending on size and sex demographics (e.g., Loseto et al, 2006;Hauser et al, 2017) and on season (e.g., Asselin et al, 2011;Hornby et al, 2016). The variability of sea-ice preference and/or avoidance reflects the indirect relationship between beluga and sea ice through sea-iceassociated prey (i.e., Arctic cod; Choy et al, 2020) or predator avoidance.…”

Cod movement ecology in a warming world: Circumpolar arctic gadids

“…Some studies indicate circumpolar Arctic gadids are occurring at a lower frequency in the diets of common Arctic predators in the US–Canadian Arctic ( B . saida : Cusset et al., 2019; Choy et al., 2020) and European Arctic ( A. glacialis : Aschan et al., 2009). Reports also indicate that large numbers of fish in the sub‐Arctic are shifting towards the Russian zone of the Barents Sea and Kara Sea, but there is limited available catch data reported from the region to confirm this hypothesis (Chernova, 2018; Eriksen et al., 2020; Havforskningsrapporten, 2015; Mueter et al., 2016).…”