Commercial whaling of bowheads ended about a century ago, but the industry’s footprint could threaten the species’ future.
Before people sought their blubber for oil and their baleen for tools and clothes, bowhead whales (Balaena mysticetus) flourished. This was despite drastic ancient climate change, including a warm period between around 8500 and 10,000 years ago. But whaling reduced global bowhead numbers to as low as 3000 individuals by the early 20th century. The US, Canada and Norway have since protected the species for decades, but it is unclear how well they are rebounding due to sparse data on pre-whaling populations.
at the University of Copenhagen in Denmark and his colleagues analysed the bowhead gene pool to decipher the effects of ancient climate change and whaling. Researchers have grappled with this question over the past two decades but the available mitochondrial DNA lacked enough clues, he says.
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The researchers extracted nuclear DNA from more than 200 ancient bowhead bones found in Canada and the Norwegian archipelago of Svalbard. They also measured the levels of carbon and nitrogen atom variants in the bones, and compiled geography data of over 800 washed-up bowhead remains dating back 11,000 years. Together, this revealed population shifts over time, along with the animals’ habitats and diets amid climatic changes.
“No matter which forces nature has thrown at them, it appears their population size has remained stable,” says , also at the University of Copenhagen and part of the team. The researchers also saw little impact from centuries of subsistence whaling by Indigenous hunters. “But commercial whaling upended this stability.”
The team estimates some populations fell by over 90 per cent during commercial whaling. They fragmented across the Arctic and their genetic diversity dropped.
Over the next millennium, the researchers estimate the genetic diversity of the Svalbard bowhead population will decline by 15 per cent – even if population sizes remain steady. “We have only seen the beginning,” says Lorenzen.
This genetic “erosion” happens slowly because bowheads are the world’s longest-lived mammals and can reach over 200 years old. They can wait decades to reproduce, says Lorenzen. From the whales’ perspective, commercial whaling ended just two or three generations ago.
In upcoming generations, only related individuals will remain and inbreeding will start becoming evident, says Westbury. Other species hit hard by commercial whaling may have similar fates, he adds.
The researchers suggest that declining genetic diversity may hobble bowheads’ adaptation to a hotter Arctic. Over the past four decades, the region has warmed nearly four times faster than the rest of the globe, and the Arctic Ocean may see ice-free summers by 2030.
The findings provide an urgent wake-up call, says at the University of Auckland in New Zealand.
“If we can protect populations and species now, limiting this decline, we give them the best chance at resilience into an uncertain future.”
bioRxiv
