Alaska Fisheries Science Center 2021 Seminar Series - Matthew Rogers
Hot tub time machine: using stable isotope analysis of Northeast Pacific humpback whale baleen to infer dynamic foraging habits and evidence of starvation in response to a marine heatwave.
From 2014-2016, researchers observed the strongest marine heatwave ever recorded in the North Pacific Ocean. Food web dynamics were disrupted during the marine heatwave, which likely caused nutritional stress in humpback whales. For the first time in this population, we analyzed nitrogen and carbon stable isotopes in humpback whale baleen to investigate whale foraging ecology before, during, and after the marine heatwave. We hypothesized that if a population-level change in foraging ecology occurred during the marine heatwave, it would be reflected in baleen isotopic patterns.
We found that individual baleen plates record 4-5 years of isotopic information in humpback whales (n=9) as inferred from annual baleen δ15N oscillations. We estimate a baleen growth rate of 16.9+/-3.9 cm/yr. We determined likely forage types for individual whales (zooplankton vs. forage fish) and observed apparent differences in nearshore vs. offshore feeding among individuals from baleen δ13C profiles. We did not find any abrupt population-level foraging shifts after the onset of the marine heatwave. We also found an anomalous, steadily increasing δ15N pattern in the most recently grown baleen of multiple whales that died during the marine heatwave, potentially indicating severe nutritional stress or starvation in the weeks or months preceding death.
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