Size and biomagnification: How habitat selection explains beluga mercury levels

Mercury (Hg) levels in the Beaufort Sea beluga (Delphinapterus leucas) population increased during the 1990s; levels have since declined but remain higher than the 1980s. The diet of this beluga population is not well-known, thus it is difficult to assess dietary Hg sources. During the summer,the Beaufort Sea belugas segregate by length, sex, and reproductive status corresponding to habitat use that may result in feeding differences and ultimately Hg uptake. To test this hypothesis, we examine beluga dietary variation using fatty acid profiles and determine which biological variables best predict diet. Relationships between biological variables and fatty acids were further evaluated with stable isotopes and Hg concentrations in liver and muscle. Fig concentrations in muscle were better related to liver delta N-15 than muscle delta N-15. Stable isotopes and fatty acids are compared in their ability to describe dietary Fig processes in beluga. Fatty acids provided support for influences of whale behavior on dietary Fig uptake, whereas stable isotopes inferred tissue Fig metabolic rates. Here, we show beluga length drives diet variability leading to differences in Fig uptake and biomagnification processes dominate beluga Fig levels over Fig bioaccumulation over time.