Common dolphins in the North Atlantic are dying much younger, with female lifespans dropping seven years since the 1990s, according to a new study. Researchers analyzing stranded dolphins in the Bay of Biscay highlight bycatch from fishing as a key threat, urging better conservation measures. The findings reveal a 2.4% slowdown in population growth, signaling risks to marine ecosystems.
A study published on October 10 in Conservation Letters by researchers from the University of Colorado Boulder has uncovered alarming trends in the longevity of common dolphins in the North Atlantic. By examining 759 stranded dolphins collected between 1997 and 2019 along the Bay of Biscay, the team determined that the average lifespan of female dolphins fell from 24 years in the late 1990s to 17 years by 2019. This decline correlates with reduced fertility rates and a 2.4% drop in population growth since 1997, far below the species' ideal 4% annual increase.
The Bay of Biscay, a nutrient-rich wintering ground off France's coast, supports about 180,000 common dolphins each year, drawn by prey like anchovies and sardines. However, it is also Europe's busiest fishing zone, where bycatch—accidental entanglement in fishing gear—claims thousands of lives annually. In 2021 alone, an estimated 6,900 dolphins died from bycatch in the bay. Traditional surveys from ships or aircraft have failed to detect these changes, as dolphins' mobility masks underlying declines.
"There is an urgent need to manage the population better," said Etienne Rouby, a postdoctoral researcher at the Institute of Arctic and Alpine Research. "Otherwise, there is a risk for decline and, ultimately, extinction." The study used growth layers in dolphin teeth to assess ages at death, revealing patterns in only 10% of total fatalities but providing sensitive indicators of health.
In response, France implemented a one-month fishing ban in January 2024 to curb bycatch. Rouby suggests timing adjustments based on dolphin migration for greater effectiveness. As top predators, common dolphins—numbering around 6 million worldwide—help regulate fish populations; their loss could destabilize ecosystems. The research calls for adaptive policies under frameworks like the European Marine Strategy Framework Directive to prevent broader cetacean declines.