Using geochemical tools to characterize the foraging habitats of Eastern Beaufort Sea beluga whales
Date
2024
Authors
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Publisher
University of Delaware
Abstract
The Eastern Beaufort Sea beluga (EBS beluga; Delphinapterus leucas) is a migratory whale known to spend its year split between the Bering and Beaufort Seas. Recently, EBS belugas have been recorded displaying unusual shifts in diet and location, as well as declining growth rates. Climate change may play a role, but with limited knowledge on EBS beluga’s diet, the exact reason for these unusual observations remains unclear. As a first step toward elucidating the pathways and effects of ongoing climate changes on EBS beluga populations, this study aims to examine the present-day foraging habitats and methylmercury exposure sources of EBS belugas, using geochemical tracers (i.e., carbon, nitrogen, and mercury stable isotopes). We first evaluated the effectiveness of these stable isotopes as habitat markers (surface vs. benthic, nearshore vs. offshore, and Bering vs. Beaufort Sea) by analyzing stable isotopes in muscle tissues of fishes from various EBS beluga feeding habitats. The results show that mercury stable isotopes effectively differentiate the geographic location of fish samples (Bering vs. Beaufort) and can distinguish between nearshore vs. offshore and pelagic vs. benthic habitats. To identify the primary foraging habitats of these whales, we compared stable isotope tracers between EBS belugas and Bering and Beaufort Sea fishes from various environments from 2011 – 2022. The biomagnification of MeHg along food chains indicates the MeHg burden in EBS beluga primarily come from nearshore Beaufort Sea food chains. Our mercury stable isotope data aligns with published EBS beluga telemetry data and diving patterns, indicating that these whales predominantly feed in offshore benthic habitats in the Bering Sea during winter and nearshore benthic habitats in the Beaufort Sea during late spring and early summer. Using both an isotope mixing model and ecosystem modeling approach, we estimated more than half of the MeHg found in EBS belugas originates from their diet in the Beaufort Sea. EBS belugas are considered a sentinel species for Arctic ecosystem changes. The results of this study provide a present-day baseline of EBS beluga foraging habits, which is a pivotal step for understanding the historical and future ecosystem changes in the Arctic and their effects on this population.
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Keywords
Belugas, Foraging habitats, Diet, Mercury stable isotope, Methylmercury, Stable isotopes