The Genetic Ecology and Population Origins of the Beluga Whales of Yakutat Bay

Small populations or groups of individuals at the edge of a species’ range can reveal much about a species’ niche preference limitations, its demographic history, and its adaptive potential for range expansion or niche shifts. We investigated whether recent sightings of small numbers of beluga whales (Delphinapterus leucas) in Yakutat Bay, Alaska, some 800 km distant from the nearest known population in Cook Inlet, represented a distinct group of whales or temporary movements beyond Cook Inlet. We also investigated whether, if a distinct group of whales, they exhibited any genetic consequences of small effective population size. Using remote biopsy sampling, mtDNA sequencing, multi-locus genotyping, and PCR-based gender determination, we found that the Yakutat whales comprised both males and females. They exhibited site fidelity across years, were significantly differentiated for mtDNA and microsatellite loci from the Cook Inlet population, and formed a distinct genetic cluster. Individual assignment methods identified Cook Inlet as the most likely origin of the Yakutat whales when compared to the four other population stocks in the western Nearctic, but individual whales had low likelihoods of coming from Cook Inlet relative to whales sampled in that population.

We developed a new exclusion-assignment method, GELATo, that estimates the likelihood of a group of whales arising within one, any, or none of a series of reference populations. Using the same five beluga whale reference populations, we confirmed the close affinity of Yakutat to Cook Inlet but excluded the Yakutat group as likely immigrants from Cook Inlet. These findings, in conjunction with recent beluga whale sightings, including young-of-the-year calves, in Yakutat Bay in all seasons, indicate a small, resident, reproductive group with limited current genetic exchange with Cook Inlet. Lower variation at neutral markers, significantly higher relatedness among and inbreeding within the Yakutat animals compared to Cook Inlet raise concerns about the loss of genetic diversity over time. While the small size and uncertain history and viability of the Yakutat group creates new management challenges, its location, unique habitat, and persistence up to now can provide insights into the survival of small groups on the warm edge of the species’ range. It is also a testament to the effective stewardship of the local Tlingit community.

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G. O'Corry-Crowe, W. Lucey, F.I. Archer, and B. Mahoney. Published in Marine Fisheries Review. dx.doi.org/10.7755/MFR.77.1.5