MEPS 471:283-291 (2012)  -  DOI: https://doi.org/10.3354/meps10029

ABSTRACT: The diet of individuals within a species commonly differs among sex and age classes because of differences in energy requirements and physiological needs. Belugas Delphinapterus leucas show a high level of sexual habitat segregation and dimorphism that could result in differences in diet between the sexes. Here, we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) from muscle and skin samples of 88 belugas, and likely prey species, to investigate how beluga diet in Cumberland Sound (Nunavut, Canada) varied between sexes, among age classes, and over time from 1982 to 2009. Based on linear mixed-effects models, older belugas had higher δ¹³C and δ¹⁵N than younger individuals of both sexes, suggesting that older individuals feed on more benthic, higher trophic-position prey than younger individuals. We also found a strong, decreasing trend in both δ¹³C and δ¹⁵N values over time, indicating either a temporal shift in beluga diet or an ecosystem-wide change in isotope values. Based on stable isotope mixing models performed on belugas sampled since 2000, both males and females fed primarily on Arctic cod Boreogadus saida and capelin Mallotus villosus. The latter is a recent invader to this ecosystem, which could explain the temporal shift in stable isotopes of the Cumberland Sound belugas.

KEY WORDS: Marine mammal · Monodontidae · Arctic · Time series