Both Female and Male Beluga Whales Take Many Mates, and It May Protect Their Genes
Beluga whales in Alaska’s Bristol Bay do not rely on dominant males or fixed pairings to reproduce. Instead, a long-running genetic study reveals that both males and females have multiple partners over many years, producing a population shaped less by competition and more by patience, repetition, and choice over time.
The findings, published in Frontiers in Marine Science, show that belugas in Bristol Bay follow a polygynandrous mating system, in which both sexes mate with multiple partners. By tracking which adults were related to which calves over multiple breeding seasons, researchers found a population made up largely of half-siblings rather than full siblings, a structure that helps maintain genetic diversity and limit inbreeding in an isolated group.
“What makes this study so thrilling is that it upends our long-standing assumptions about this Arctic species,” said senior author Greg O’Corry-Crowe, in a press release.
Beluga Whale Reproduction in an Isolated Population
Over 13 years, the research team collected small tissue samples from more than 600 beluga whales in Bristol Bay, a population estimated at roughly 2,000 animals that has had little mixing with other beluga groups. Because belugas can live for many decades, the researchers focused on mating patterns that unfold within a single breeding season or across a few years, rather than attempting to track reproduction across an entire lifetime.
Belugas swim together in the sea off Alaska.
(Image Credit: Photo taken by Lisa Barry with permission from NOAA Fisheries)
Their goal was to determine which broad mating system best described the Bristol Bay population: one dominated by males mating with multiple females, one driven by females mating with multiple males, or a system in which both sexes have multiple partners over time.
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Male and Female Belugas Use Different Strategies
Because males are much larger than females and appear to invest little time in caring for calves, the team had expected a strongly polygynous system, in which a few dominant males secured most matings through competition. Instead, the data pointed to a more distributed pattern of reproductive success.
“Beluga males were indeed polygynous, but, surprisingly, only moderately so,” said O’Corry-Crowe, in a press release. “However, a long life may also be key. Belugas can live 90 years, possibly more. Male beluga whales may, therefore, play a long game of securing a few matings each year over a very long reproductive life.”
Rather than competing intensely within a single breeding season, males appear to accumulate reproductive success gradually over decades.
Female belugas followed a different strategy. Genetic profiles showed that females frequently switched mates from one breeding season to the next, rather than repeatedly pairing with the same male. That pattern suggests a form of reproductive risk management, allowing females to avoid pairing repeatedly with low-quality or closely related males.
“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,” said O’Corry-Crowe.
Why Beluga Whale Mating Systems Matter for Conservation
Despite its small size and isolation, the Bristol Bay beluga population showed relatively high genetic diversity and low levels of inbreeding. Comparisons with other beluga populations and historical samples suggest that this diversity has remained stable over time, rather than declining as often occurs in small groups.
The findings highlight the role of mating systems in shaping genetic outcomes. When reproduction is concentrated among only a few individuals, the effective population size shrinks, increasing the risk of inbreeding even if the overall population appears healthy. By spreading reproduction across many males and females, the Bristol Bay belugas appear to limit how closely related individuals are across generations.
“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 authors note that mating systems may vary across beluga populations, but the results underscore how behavior can influence genetic resilience, particularly in small or isolated groups. The research was carried out in collaboration with Indigenous communities in Bristol Bay, whose participation made long-term sampling possible.
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