As Humpback Whale Populations Recover from Whaling, Older Males Are Winning the Mating Game

Commercial whaling did not merely reduce whale populations. It removed the oldest animals most systematically - the largest, the most accessible, the ones most likely to be encountered and killed. What that left behind was a population skewed young, stripped of its oldest members, and fundamentally different in structure from what had existed before exploitation began. The consequences for how these animals live, compete, and reproduce have only recently become possible to study.

A research team led by the Sea Mammal Research Unit at the University of St Andrews used 18 years of data from humpback whales breeding in New Caledonia in the South Pacific to track what happened as the population recovered. Their findings, published in Current Biology, describe a shift in the reproductive landscape as older males became more common: they became substantially better at fathering calves than younger rivals.

How the study was conducted

Humpback whales have never been observed mating in the wild, which has historically made it impossible to know who fathers a calf. The research team worked around this by applying genetic analyses to skin samples - small biopsies that can be taken non-invasively from a living whale - to identify paternity through DNA matching. Age estimates came from an epigenetic molecular clock, a technique that reads chemical modifications on DNA to estimate biological age from the same small tissue sample.

Long-term field data on male behavior were provided by the NGO Operation Cetaces, which has monitored humpback whales in New Caledonia for decades. This combination of genetic, epigenetic, and behavioral information gave the researchers an unusually complete picture of how individual males competed and reproduced across the study period.

What the recovery revealed

In the early years of the monitoring period, the population was dominated by young males - a legacy of whaling's selective removal of older animals. Over time, as overall numbers grew, the age distribution shifted toward something more balanced. Crucially, as older individuals became more common, they became increasingly successful at siring offspring compared to their younger competitors.

Senior author Dr. Ellen Garland noted: "Mating behaviour, 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."

Humpback males are famous for producing some of the most acoustically elaborate displays in the animal kingdom. Their songs carry across breeding grounds and are widely assumed to play a role in attracting mates. Males also physically escort females or engage in competitive groups where multiple males jostle for proximity. The new data suggest that older males are better at one or more of these behaviors - either through experience in refining their tactics, or through physical advantages that come with full maturity, or because females prefer them.

What we missed by studying a shifted baseline

Lead author Dr. Franca Eichenberger pointed to a deeper epistemological problem the study reveals: "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 behaviour, competition, and reproduction."

Almost all modern behavioral research on humpback whales was conducted during or after the whaling era. Scientists never studied these behaviors in an unexploited, age-balanced population. What passed as baseline knowledge - who sings, who escorts females, who reproduces - reflected a population in a historically aberrant state. As recovery continues, the baseline itself is moving, and so is the science.

The findings have implications for conservation monitoring. Understanding how population recovery affects reproductive dynamics and behavior is important for assessing whether a recovering species is truly approaching its ecological role or simply increasing in numbers while other aspects of its biology remain distorted. The researchers argue strongly for continued long-term monitoring of previously exploited whale populations precisely because these changes unfold slowly and were not visible until nearly two decades of data accumulated.