Cetacean scientists have raised concerns that the lifespan of common dolphins in the Bay of Biscay are getting shorter.
According to a new study in the journal Conservation Letters, the lifespan of female common dolphins has become seven years shorter on average – reducing from 24 to 17 years – and population growth has slowed by 2.4 percent.
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“The numbers are likely to be lower in reality,” says Etienne Rouby, a postdoctoral researcher at the Institute of Arctic and Alpine Research at University of Colorado Boulder. If this trend continues, the population could go into decline.
The scientists examined 759 individuals that stranded along the Bay of Biscay between 1997 and 2019. To find out how old they were, they cut the teeth in half and counted the annual growth rings – in the same way that you might count the rings of a tree.
Researchers often study marine animal populations through sightings data. But for animals like dolphins that swim huge distances across the open ocean, this method is “logistically impractical,” the researchers say in the paper. “Stranding data provide an alternative to conventional monitoring.”
If females aren’t living as long, they have less time to produce healthy calves. “This represents two to three fewer breeding events per female on average,” says the study. “This result is alarming as it indicates reduced lifetime reproductive success essential for maintaining population viability.”
The findings highlight the “urgent need to manage the population better," says Rouby. "Otherwise, there is a risk for decline and, ultimately, extinction."
Dolphins play an important part in keeping the ocean healthy. “They are typically at the top of the food chain, which helps control the populations of lower trophic level species,” says Thea Taylor, managing director of Sussex Dolphin Project who wasn’t involved in the study. “They also serve as excellent indicator species, providing valuable insights into the health of the wider ecosystem” because toxins that built up in the food chain accumulate in the dolphins’ blubber.
“A decrease in the lifespan of these animals is always a concern, as it indicates larger problems within our marine environment,” she says.
There are millions of common dolphins around the world and more than 180,000 visit the Bay of Biscay each winter. But it is also a busy fishing area. Around 6,900 common dolphins were unintentionally caught as bycatch in 2021.
For Rouby, the study highlights the urgent need for measures to protect marine animals. “We need to act before it is too late,” he says.
