The Promiscuous Lives of Beluga Whales

Explore

BElugas and other toothed whales such as dolphins are known to live in stable groups, usually led by an older matriarch. How does the reproduction dynamic play out in belugas (Delphinapterus leucas), is however difficult to determine. They inhabit northern habitats, often confined by ice, making observations of behavior frigid and difficult.

In a study published today in Frontiers of marine sciencewildlife biologists from Florida Atlantic University and the Alaska Department of Fish and Game used genetic tools to uncover the mating habits of wild beluga whales. The team genetically profiled skin samples collected over 13 years from 623 beluga whales inhabiting Bristol Bay, Alaska, in collaboration with local indigenous communities. In this isolated population of around 2,000 whales, movements outside the group, and therefore genetic exchanges, are rare. Thus, genetic profiles should reveal mating dynamics within the population.

The study authors expected to find that males competed intensely for mates and mated with multiple females, in a polygamous system. Male belugas provide little parental care, and extreme sexual dimorphism – with males heavier and up to 25% longer than females – generally indicates a species whose males compete for demanding females.

Read more: “Toppling the patriarchy through ecstatic sex”

The results showed that beluga fathers had on average significantly more calves than mothers, reflecting their lower investment per offspring. However, both males and females were polygamous, associating with multiple partners in separate breeding seasons. Most of the calf siblings detected in the genetic data were half-siblings that shared a single parent, rather than the full siblings that would be seen if a pair of whales bred more than once.

The researchers hypothesize that the long reproductive life of beluga whales, whose lifespan can exceed 100 years, reduces the selective pressure of competition between the sexes thanks to the numerous mating opportunities over time. “Rather than competing intensely over the course of a single season, males appear to play the long game, spreading their reproductive efforts over many years. This appears to be a ‘take your time, there are plenty of fish in the sea’ strategy,” study author Greg O-Corry-Crowe said in a statement.

As for females, changing their partner between breeding seasons could spread their risks of bad choices. If they unintentionally mate with a low-quality male, they will still have other opportunities to produce healthy offspring with other males.

The result of all this mate swapping on the population was lower than expected levels of inbreeding, ensuring higher levels of genetic diversity. “Polygynandy during breeding seasons leads to long, loose pedigrees that can reduce inbreeding and maintain diversity, even in small populations. [size]”, the study authors concluded in the article.

Mating dynamics can be a strategic way to continue mixing within a small, isolated group.

Enjoy Nautilus? Subscribe for free to our newsletter.

Main image: Matthias Brix / Shutterstock

• Devin Reese

  Published on January 21, 2026

  Devin Reese is the editor-in-chief of Natural history and a science writer based in Alexandria, Virginia.