MEPS 579:213-225 (2017)  -  DOI: https://doi.org/10.3354/meps12256

ABSTRACT: Declines in individual growth rates in eastern Beaufort Sea (EBS) beluga whales Delphinapterus leucas over the past 20 yr are hypothesized to be the result of changing environmental conditions. To better understand short-term variation in diet, we examined inter-annual variation in body condition indices, fatty acid composition, and stable isotope ratios in EBS beluga whales in relation to environmental conditions. We also examined if differences in dietary tracers in beluga whales reflect sex- and size-based habitat selection. During a warm year anomaly (2012), belugas demonstrated greater overlap in dietary tracers among sex and size classes, whereas greater differences occurred during years with greater sea ice extent over the Mackenzie Shelf (2013 and 2014). Body condition indices (maximum girth and blubber thickness) were highest in belugas in 2011 and 2012 and lowest in 2014. Total Calanus markers 20:1n-9 and 22:1n-11 contributed the most to annual variability and had the lowest proportions in females and small males in 2014, a year that coincided with low Arctic cod Boreogadus saida biomass. Age and year were the strongest predictors of fatty acid composition and δ¹³C values in beluga whales, whereas length influenced δ¹⁵N values, possibly a reflection of larger whales diving to greater depths to feed on Arctic cod. Annual variability in sea ice conditions and prey availability may be associated with inter-annual variation in dietary tracers and condition in beluga whales. As Arctic marine ecosystems are currently undergoing rapid change, understanding the factors causing inter-annual variation in diet should be a conservation priority for this beluga whale population.

KEY WORDS: Fatty acid signatures · Delphinapterus leucas · Beaufort Sea · Arctic · Stable isotope ratios · Climate change · Dietary tracers · Body condition