Seasonal flexibility in energy stores of Hudson Bay beluga whales: insights from blubber lipid analysis

During the primary feeding season, marine mammals often accumulate fat reserves, primarily in the form of blubber. Despite the ecological significance of feeding, uncertainty remains surrounding the timing of energy store accumulation in Hudson Bay beluga whales (Delphinapterus leucas (Pallas, 1776)). Blubber samples were collected from whales hunted by Inuit along the whale’s migration route, from 2015 to 2021 (excl. 2018). Sampling occurred in spring and fall, assumed to represent feeding in winter and summer, respectively. We analyzed blubber for lipid content and adipocyte size, two related indices of lipid dynamics, across three blubber sections (outer, middle, and inner). We found interannual variability in the season with the highest fat content, with some years showing higher lipid content in spring than fall. While adipocyte size did not differ seasonally, minima were observed in 2017 and 2019. Fat stores differed across blubber sections, with the highest lipid content and largest adipocytes in the middle section. The observed seasonal variation indicates there is no consistent season in which Hudson Bay beluga whales predominantly accumulate fat. Consequently, building energy stores in the form of blubber may not be the primary driving force behind the beluga whale’s migration between the wintering and summering areas.