Importance of Eating Capelin: Unique Dietary Habits of Hudson Bay Beluga

Abstract

Beluga whales (Delphinapterus leucas) fill an important ecological and economic role in Hudson Bay. However, little is known about their diet and a better understanding of beluga populations is required. Though Arctic cod (Boreogadus saida) are important forage fish species for many circumpolar marine predators, beluga are opportunistic feeders and may feed on a variety of prey items. Here, we compare the fatty acid profile of two key forage fish, Arctic cod and capelin (Mallotus villosus), to determine the relative importance of each species to the diets of beluga during the 1980s in three Canadian Eastern Arctic beluga populations: Western Hudson Bay, Cumberland Sound, and the High Arctic. First, we compared the two prey species using a Principle Component Analysis (PCA) to determine the fatty acids that best described each species. Five fatty acids dominated the Arctic cod profile (the 20 and 22 carbon length monounsaturates 20:1n7, 20:1n9, 22:1n9, 22:1n11, 22:1n7), and five fatty acids were representative of the capelin profile (18:2n6, 16, 22:6n3, 22:5n6, and 20:4n6). The levels of these ten fatty acids were significantly different between the two fish species. A discriminant function analysis followed by univariate tests, were performed on beluga fatty acid profiles to determine if populations could be differentiated. Results demonstrated significant differences among the three beluga populations. Finally, to examine the qualitative dietary importance of Arctic cod and capelin among the three beluga populations all fatty acid profiles were evaluated together with a PCA. We found the fatty acid profiles that segregated the Hudson Bay beluga population from others appeared to be associated with a capelin diet relative to the other beluga populations that appeared to feed more heavily on Arctic cod. The difference in fatty acid profiles and diet between the northern populations and the Hudson Bay population is discussed relative to possible environmental explanations.