Among marine mammals, beluga whales (Delphinapterus leucas) are particularly difficult to study in their icy habitat. To better understand and protect this endangered species, scientists must piece together bits of their lives from fragments, including one of the most important behaviors of any species—mating.
One small population of beluga whales living in southwest Alaska’s Bristol Bay appears to have a surprising strategy. Over several years, both male and female belugas mate with multiple partners. This method may reduce the risk of inbreeding in the group of just 2,000 whales and help maintain genetic diversity. The findings are detailed in a study published today in the journal Frontiers in Marine Science.
A surprising strategy
Over 13 years, scientists collected genetic samples from 623 beluga whales in Bristol Bay, while simultaneously observing their ages and social groupings. The largely isolated population has little or no mixing with other populations elsewhere in the Arctic and subarctic. This degree of isolation gives biologists a unique opportunity to study them as a distinct population.
The team wanted to determine which mating style this population of beluga engaged in—polygynous, polyandrous, or polygynandrous. In polygynous mating, one male mates with multiple females, as seen in many bird species. In polyandrous animals, one female mates with multiple males, similar to what female mice do. Polygynandrous mating is when both males and females have multiple mates.
Since belugas live 30 to 50 years on average—with some living as long as 80 years—the team focused on what happens during one mating season instead of over a whole lifetime.
The team found that this beluga whale population engages in a polygynandrous system, where both males and females mate with multiple partners over several years. Instead of reproductive success being dominated by a few individuals, it is more spread out. This mate switching also results in many half-sibling offspring and few full-sibling offspring and could reduce the risk of inbreeding and help maintain genetic diversity in the small population.
According to the team, these findings upend scientists’ earlier notions about beluga mating. Since males are much larger than females and are not frequently seen with mothers and calves, researchers thought that the whales were highly polygynous. In these settings, males spend significantly more time competing for mates and only a few dominant males end up fathering most of the calves.
“Our findings tell a very different story,” Greg O’Corry-Crowe, a study co-author and biologist at Florida Atlantic University, said in a statement. “In the short term, males are only moderately polygynous. One explanation we think lies in their incredible longevity—belugas can live perhaps 100 years or more. Rather than competing intensely in a single season, males appear to play the long game, spreading their reproductive efforts over many years. It appears to be a ‘take your time, there’s plenty of fish in the sea’ strategy.”
Mating matters
The findings also indicate that female belugas have their own equally fascinating reproductive strategy. Instead of sticking with one partner, they frequently switch mates from one breeding season to the next. This could be a form of risk management, allowing the females to avoid pairing with low-quality males and increasing the likelihood of creating healthy and genetically diverse offspring.
“It’s a striking reminder that female choice can be just as influential in shaping reproductive success as the often-highlighted battles of male-male competition,” O’Corry-Crowe added. “Such strategies highlight the subtle, yet powerful ways in which females exert control over the next generation, shaping the evolutionary trajectory of the species.”
Greg O’Corry-Crowe and Cortney Watt, Arctic Whale Research Program – FAU/DFO.
According to the team, these findings underscore how important understanding mating systems is for conservation methods, particularly in small or isolated populations like the Bristol Bay Belugas. In polygynandrous systems like these, mate choice, partner switching, and shared reproductive opportunities is what spreads genes more evenly. This maintains genetic diversity, limits inbreeding, and offsets the devastating impacts a small population size can have.
“Understanding these dynamics matters for conservation. If only a few males father most calves, the effective population size becomes much smaller than the number of whales actually present,” said O’Corry-Crowe.
The Indigenous communities of Bristol Bay were key in getting this study together. They helped study these elusive whales, melding scientific research with Indigenous knowledge to protect the belugas in a changing Arctic and subarctic.
“We cannot afford to be complacent. Small populations still face the dangers of genetic erosion,” concluded O’Corry-Crowe. “But we can be optimistic that beluga whale mating strategies provide evidence of nature’s resilience and offers hope for those working to save and recover small populations of any species.”
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