Bristol Bay belugas use diverse mating to maintain genetic health despite small numbers.

A 13-year study of Bristol Bay’s beluga whales reveals both males and females mate with multiple partners over decades, creating a polygynandrous system that maintains high genetic diversity despite a small population of about 2,000. DNA analysis of 623 whales shows most calves are half-siblings, indicating frequent mate switching. Males exhibit moderate polygyny, likely due to long lifespans up to 90 years, while females change partners between seasons, possibly to avoid inbreeding or poor-quality mates. This reproductive behavior boosts genetic resilience, preventing inbreeding and increasing effective population size. The research, conducted with Indigenous communities, underscores how mating patterns support long-term survival and informs conservation strategies.