Bristol Bay, Alaska is home to one of the smallest and most isolated beluga whale populations left — roughly 2,000 animals, cut off from other beluga groups and watched closely by biologists worried about what small, cornered populations usually do over time: inbreed, lose genetic diversity, and become more vulnerable to disease and environmental shocks. Working with the Alaska Department of Fish and Game and Alaska Native subsistence hunters from the region, a team led by Dr. Greg O'Corry-Crowe at Florida Atlantic University spent thirteen years collecting small tissue samples during the local harvest, eventually building a DNA dataset spanning 623 individual belugas.
Despite only 2,000 animals left, this beluga population's genetic diversity rivals populations many times its size.
What the genetics revealed, published in Frontiers in Marine Science, was a mating system far more fluid than researchers expected. Both males and females reproduce with multiple partners across their lifetimes, and when calves turned out to have siblings, those siblings typically shared only one parent rather than both — evidence of widespread extra-pair reproduction running through the population. Males did show some polygyny, with certain individuals siring more offspring than others, but the imbalance was far less extreme than models had predicted for a species that lives in tight-knit pods.
What the Genetics Show
O'Corry-Crowe has a theory for why courtship in belugas doesn't concentrate around a few dominant males the way it does in many land mammals: "The three-dimensional aquatic environment likely limits a male's ability to successfully court or corral multiple females." He also points to beluga longevity — the whales can live past 90 years — as part of the picture, giving individuals many separate breeding opportunities across a long life rather than one narrow mating season to compete in.
The payoff shows up directly in the genetics. Despite numbering only around 2,000 animals, Bristol Bay's belugas carry genetic diversity comparable to far larger populations, with little evidence of inbreeding, and that diversity has stayed stable over time. Frequent mate-switching spreads reproduction across more individuals, which limits how many closely related whales end up breeding with each other — a built-in defense against the genetic bottlenecking that threatens small, isolated populations as the Arctic they depend on keeps changing around them.
Image credit: Beluga whale at surface