Humpback whale recovery is changing who fathers the calves

Whaling once pushed many large whale species to the edge of extinction. Although hunting has long since stopped, its effects did not end with declining numbers. Even decades later, the legacy of whaling continues to shape whale populations, affecting not only how many whales exist today but also which males succeed in fathering calves.

Two Decades of Data From South Pacific Whales

Researchers analyzed nearly 20 years of data from humpback whales that breed in the waters around New Caledonia in the South Pacific. The study relied on long term monitoring carried out by the NGO Opération Cétacés. Using this extensive dataset, scientists investigated how the population's age structure, male behavior, and paternity patterns have changed over time.

During the early years of population recovery, breeding groups were largely made up of younger males. As whale numbers increased, the population gradually developed a more balanced mix of younger and older individuals. As older whales became more common, they also became more successful at fathering calves than their younger competitors.

Genetic Tools Reveal Hidden Fathers

Humpback whales have never been directly observed mating in the wild, which means the identity of a calf's father has historically been unknown.

To solve this mystery, the international research team led by the Sea Mammal Research Unit at the University of St Andrews used genetic testing to determine paternity. They also used a technique known as an 'epigenetic molecular clock' to estimate the age of individual whales. Both pieces of information could be obtained from a small skin sample collected from the animals.

Whale Songs and Competition for Mates

Male humpback whales are famous for producing some of the most elaborate songs in the animal kingdom. These powerful vocal performances can carry across large areas of the breeding grounds and are believed to play an important role in attracting females. Males may also accompany females closely or compete directly with rival males in intense physical encounters.

Senior author Dr. Ellen Garland of the Sea Mammal Research Unit explained, "Mating behavior, and who was successful at mating, changed with these shifts in age structure. As the population recovered, there were more older males than expected singing, escorting females, and successfully fathering calves compared to younger animals."

The results suggest that male humpback whales likely need years to develop and perfect both their songs and their competitive strategies. This experience may give older whales a clear advantage when competing for mates. As populations continue to grow, females may also become more selective, which could further favor males with stronger displays or other desirable traits.

The Long Shadow of Whaling on Whale Behavior

The findings highlight the importance of continued research on recovering whale populations. Long term studies help scientists understand how past exploitation continues to influence population structure, competition, and reproduction.

The research also points to a broader issue in whale science. Much of what scientists know about whale behavior comes from studying populations that had already been heavily impacted by whaling. In other words, researchers have been working from a shifted baseline rather than observing completely undisturbed populations.

Dr. Franca Eichenberger, lead author of the study from the Sea Mammal Research Unit at the University of St Andrews, said, "It is only now, as whale populations recover and new analytical tools become available, that we are beginning to understand how far-reaching the consequences of whaling truly are. The impacts extend beyond population size -- they shape behavior, competition, and reproduction."

Dr. Eichenberger added, "Virtually all populations of whales have changed due to whaling; our work shows that they continue to change as they recover. This is why the continued long-term monitoring of previously exploited whale populations is so important. Humpback whales have shown a remarkable comeback over recent years. Now is the time we can learn so much more about their behavior and life history. We just need to keep looking."