In recent years, the common dolphin population in the Bay of Biscay has shown increasingly worrying signs. Accidental catches linked to fishing activities and other human-related pressures at sea are significantly affecting the survival of the species. A recent scientific study revealed a notable decline in the lifespan of female dolphins, a trend that, combined with low fertility, poses a serious threat to the stability of the population.
The increase in accidental catches in the Bay of Biscay
Since 2016, the accidental capture of dolphins in the Bay of Biscay has increased sharply. Each winter, hundreds and sometimes more than a thousand common dolphins (Delphinus delphis) are found stranded dead along the French Atlantic coast.
In response to this alarming situation, the Conseil d’État confirmed in 2023 the need for strong and appropriate measures. Among them is the ban on fishing gear that may cause bycatch, once again enforced in the Bay of Biscay from January 21 to February 20, 2026, as previously implemented in 2024 and 2025.
The role of Observatoire PELAGIS in dolphin research
The Observatoire PELAGIS (La Rochelle Université – CNRS) was tasked with assessing the vitality of the dolphin population over the last twenty years.
This work has been made possible thanks to the Réseau National Echouages (RNE), a large national citizen science network coordinated by the observatory and supervised by veterinarians.
Each year, the network records the number of stranded dolphins, while its members also collect biological tissue samples essential for scientific research and health monitoring.
Dolphins as indicators of ocean health
According to researchers from Observatoire PELAGIS, the annual strandings represent evidence of major disruptions in marine ecosystems.
These changes also affect species that occupy the top levels of the food chain, such as dolphins. Because of this position, dolphins act as sentinels of ocean health.
A decline in dolphin population vitality is therefore considered an indicator of imbalance in the marine environment.
Challenges in studying dolphin demography
Studying the demography of the common dolphin remains a complex but essential task.
Researchers explain that although it is the most abundant cetacean species in the northeastern Atlantic, the common dolphin is highly mobile. This makes it difficult to track individuals throughout their entire lifetime.
The scientific study on declining longevity
Tissue samples collected from stranded dolphins allow scientists to determine the age of animals at the time of death.
This careful work provides the data needed to evaluate population vitality. The Observatoire PELAGIS also developed an innovative model, recognized by international scientific communities.
The research resulted in the study “Longevity Collapse in Dolphins: A Growing Conservation Concern in the Bay of Biscay”, published in Conservation Letters.
The analysis revealed a worrying finding: between 1997 and 2019 the lifespan of female common dolphins decreased by seven years.
This decline is linked to increased mortality associated with human activities at sea.
Low fertility and early mortality: a threat to the population
The study shows that the lifespan of female common dolphins in the Bay of Biscay has fallen from 24 to 17 years in just two decades.
Females begin reproducing at around 7 years of age and give birth to only one calf every two to three years.
This low fertility, combined with increasingly early mortality, seriously threatens the survival of the population.
European Union requests and protection measures
According to Observatoire PELAGIS researchers, the seriousness of this demographic situation had already been acknowledged.
In 2022, the European Commission sent a formal notice to France, requesting the implementation of stricter protection measures. Similar requests were later addressed to Spain and Portugal.
Developing policies capable of balancing dolphin conservation with the sustainable development of human activities, including fishing, will remain a priority in the coming years.