New research from the University of St Andrews shows that the role of age in male humpback whale (Megaptera novaeangliae) reproduction has changed as populations recover from centuries of exploitation.
There has been little research on the evolutionary consequences of whaling. This is despite whaling being one of the most dramatic and well-documented examples of human exploitation of wild animal populations.
Whaling drove many large whale populations to the brink of extinction. But its legacy runs deeper than a drastic decline in numbers. Decades after commercial whaling ended, its impacts continue to shape whale populations, influencing not just how many whales there are, but which males get to reproduce.
The study assessed nearly two decades of data from humpback whales breeding in New Caledonia in the South Pacific. Drawing on long-term monitoring conducted by the NGO Opération Cétacés, the scientists examined changes in age structure, behaviour, and paternity in male whales.
The scientists found that during the early years of recovery, the population was dominated by young males. Over time, as overall numbers increased, the age structure shifted to a more even age distribution amongst older and younger males. Importantly, as older individuals became more common, they became increasingly successful at siring offspring compared to younger males.
Humpback whales have never been observed mating in the wild, meaning that who fathers a calf remained largely unknown until now.
The international team led by the Sea Mammal Research Unit at the University of St Andrews applied genetic analyses to identify paternity and used a so-called ‘epigenetic molecular clock’ to estimate the age of individual whales; all from just a small piece of whale skin.
Male humpback whales are famous for producing some of the most elaborate songs in the animal kingdom. Their powerful vocal displays can often be heard far across breeding grounds and are thought to play a role in mating. Males may also escort females or engage in intense physical competition with rival males.
The findings suggest that male humpback whales may need time to learn and refine their singing and competitive tactics, giving experienced males a clear advantage. Additionally, as the population grows, females may also become more selective, which could lead to more success among males with favourable traits or the strongest performance.
The new study highlights the importance of ongoing research on recovering whale populations to understand how the consequences of exploitation shape population dynamics and reproduction over time. It also shows how most of our knowledge has come from studying a shifted baseline – scientists never actually studied these behaviours in an unexploited population as all modern research came during or after whaling.
The research appears in the journal Current Biology, titled “Changes in age-related sexual selection in a humpback whale population recovering from exploitation”.
