Strategic Sex: Alaska's Beluga Whales Swap Mates for Survival

An aerial view of a large aggregation of adult beluga whales in a bay during the summer in the High Arctic. (Photo credit: Greg O'Corry-Crowe and Cortney Watt, Arctic Whale Research Program - FAU/DFO)

In the icy waters of Alaska's Bristol Bay, a new study reveals how a small population of beluga whales (Delphinapterus leucas) survive the long haul through a surprising strategy: they mate with multiple partners over several years. The combination of long-term genetics, observation and careful analysis is starting to reveal some of the most intimate insights into one of the Arctic's most elusive whales.

Beluga whales live in a world that's difficult for scientists to observe, so surprisingly little is known about how they choose mates, compete for partners, or raise their young in the wild.

Researchers from Florida Atlantic University 's Harbor Branch Oceanographic Institute in collaboration with the Alaska Department of Fish and Game, and the North Slope Borough Department of Wildlife Management in Alaska, are the first to uncover how wild beluga whales mate, who fathers which calves, and how these reproductive strategies influence genetic diversity and inbreeding.

Over 13 years, researchers collected genetic samples from 623 beluga whales in Bristol Bay, while also observing their social groupings and ages. This population is composed of about 2,000 whales and is largely isolated, with little or no mixing with other populations, offering a unique opportunity to study them as a distinct population.

Because belugas are long-lived, researchers focused on short-term mating strategies - what happens in a single breeding season or across a few years - rather than an entire lifetime. They wanted to determine if beluga whales in Bristol Bay were polygynous, where one male mates with multiple females; polyandrous, where one female mates with multiple males; or possibly polygynandrous, where both males and females have multiple mates.

Published in Frontiers in Marine Science, the study reveals that this beluga whale population engages in highly strategic mating - a polygynandrous system. Both males and females mate with multiple partners over several years. Variance in reproductive success among individuals is moderate rather than being dominated by just a few individuals. This "mate switching" results in many half-siblings and few full-siblings and may reduce the risk of inbreeding and help maintain genetic diversity despite the population's small size and isolation.

"What makes this study so thrilling is that it upends our long-standing assumptions about this Arctic species," said Greg O'Corry-Crowe, Ph.D., senior author, a research professor of Wildlife Evolution and Behavior at FAU Harbor Branch and a National Geographic Explorer. "Because males are much larger than females and appear to spend little time associating with mothers and calves, scientists believed belugas were likely to be highly polygynous, where males spend a lot of time competing for mates and only a few dominant males fathering most of the calves. Our findings tell a very different story. 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."

Meanwhile, findings from the study show that females have their own equally fascinating reproductive strategy. Rather than sticking with a single partner, they frequently switch mates from one breeding season to the next. This behavior may serve as a form of risk management, allowing females to avoid pairing with low-quality males and increasing the likelihood of producing healthy, 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," said O'Corry-Crowe. "Such strategies highlight the subtle, yet powerful ways in which females exert control over the next generation, shaping the evolutionary trajectory of the species."

Interestingly, researchers did not find any differences between older and younger adults in terms of how many had young calves in the population at any one time, for either males or females. However, older mothers had more surviving calves than younger ones, suggesting experience, body condition, and mate choice boost reproductive success. Most adults - male and female - had only a few offspring at a time, reflecting slow female reproduction, and the fact that males father only a small number of calves each year.

The study underscores the importance of considering mating systems in conservation, especially for small or isolated populations. In polygynandrous systems, mate choice, partner switching, and shared reproductive opportunities spread genes more evenly, maintaining genetic diversity, limiting inbreeding, and offsetting the deleterious impacts of small effective population size. This helps buffer against genetic drift, which can otherwise erode diversity when only a few individuals reproduce.

"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. "This loss of genetic diversity increases the risk of inbreeding and reduces the population's ability to adapt to environmental change. Frequent mate switching combined with low reproductive 'skew' and possibly the active avoidance of mating with close relatives, may be effective strategies to maintaining the genetic health of relatively small populations."

Much of the motivation for this study came from the Indigenous communities of Bristol Bay who worked with the team of scientists to conduct the research and to meld scientific research with Indigenous knowledge as a means to protect and co-manage beluga whales in a changing Arctic and sub-arctic. Their partnership was invaluable to the success of the project.

"We cannot afford to be complacent. Small populations still face the dangers of genetic erosion. 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," said O'Corry-Crowe.

Study co-authors are Lori Quakenbush, Alaska Department of Fish and Game, Arctic Marine Mammal Program; Tatiana Ferrer, coordinator of research programs, FAU Harbor Branch; and John J. Citta, Ph.D., and Anna Bryan, Alaska Department of Fish and Game, Arctic Marine Mammal Program.

This research was supported by the Alaska Beluga Whale Committee, the Alaska Department of Fish and Game, the National Marine Fisheries Service, the North Pacific Research Board, NOAA, and FAU Harbor Branch.

-FAU-