ESR 36:77-87 (2018)  -  DOI: https://doi.org/10.3354/esr00890

ABSTRACT: Beluga whales Delphinapterus leucas that reside in Cook Inlet (CIBW) are important to coastal Alaska Native culture and subsistence, tourism, and ecologically as a top-level predator. Due to a ~50% population decline in the 1990s, the distinct population segment in Cook Inlet was designated depleted under the Marine Mammal Protection Act in 2000 and listed as endangered under the Endangered Species Act in 2008. Diet changes are a concern in CIBW lack of recovery, but beluga feeding ecology is difficult to study. Skulls from 20 CIBW and tooth growth layer groups (GLGs) from 26 individual CIBW showed decreasing trends for both nitrogen and carbon stable isotope ratios (expressed as δ¹⁵N and δ¹³C values) from 1962 to 2007. The decline in δ¹⁵N values (~1 to 2‰) could indicate a trophic level shift, but the magnitude of decline in δ¹³C values (~3‰) is much greater (>5 times greater) than expected for a trophic level shift. A shifted baseline or increased use of freshwater prey could explain the decline in δ¹³C values. We compared the strontium isotope composition (⁸⁷Sr/⁸⁶Sr ratios) of GLGs with rivers that flow into Cook Inlet and used δ¹⁵N values from the essential amino acid phenylalanine to determine that declining δ¹³C values may be explained by 2 scenarios: (1) CIBW foraged in the same location while the environmental isotopic baseline changed, or (2) CIBW foraged in a different location with a different baseline. This study presents the first evidence for a long-term (~50 yr) change in CIBW feeding ecology.

KEY WORDS: Strontium · Carbon · Nitrogen · Dietary change · Delphinapterus leucas · Northern Gulf of Alaska

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Cite this article as: Nelson MA, Quakenbush LT, Mahoney BA, Taras BD, Wooller MJ (2018) Fifty years of Cook Inlet beluga whale feeding ecology from isotopes in bone and teeth. Endang Species Res 36:77-87. https://doi.org/10.3354/esr00890 Export citation Share:    Facebook - - linkedIn