New studies indicate that the trend is alarming. Common dolphins, once the most abundant cetaceans in the world, are experiencing a decreasing lifespan in the North Atlantic. An international team of marine biologists studied 759 common dolphins to understand the phenomena. These dolphins had previously stranded on the shores of the Bay of Biscay from 1997 to 2019. Their findings reveal a concerning trend: female common dolphins’ average lifespan has decreased dramatically from 24 years in the late 1990s to just 17 years two decades later.
It is estimated that 6 million common dolphins range across tropical and temperate oceans worldwide. As a keystone species, these marine mammals are a fundamental part of productive ecosystems. The Bay of Biscay, off the French coast, is an important wintering habitat for these animals. It’s a deeply troubling trend that was just confirmed by recent data. Their population growth rate in this key common dolphin region has recently declined by 2.4% per year over the last two decades. This is especially worrisome because a healthy population should be growing at a rate of 3 to 4% per year.
Impacts of Fishing and Ecosystem Health
It emphasizes that common dolphins stand out as one of the apex predators in the Bay of Biscay. Their role extends to keeping the balance in the marine ecosystem. With this in mind, a decrease in their population would create a domino effect of negative impacts.
“Without these predators, fish populations could become out of control, and they would in turn consume too much plankton and vegetation until the system collapses,” – Etienne Rouby.
The study further identifies bycatch from fishing operations as the second-most important threat affecting common dolphin populations. In 2021, an estimated 6,900 common dolphins died due to bycatch during fishing activities in the Bay of Biscay, which had a winter population of around 180,000. Given that the vast majority of dolphins impacted will experience immediate population-level effects, this is a red flag. It has a negative impact on the health of our marine ecosystem.
In direct response to these research findings, the French government has taken steps to protect common dolphins. Rules established since 2024 prevent fishing in the Bay of Biscay every January for a month. These efforts are a positive sign of the federal government taking a proactive effort to reduce human-imposed harms to dolphin populations.
Indicators of Population Health
To address this question, the research team sought to understand how survival and fertility rates have changed in common dolphins. They acknowledged that these were delicate barometers of the public’s health. As Etienne Rouby noted, “We wanted to capture changes in the population’s survival and fertility rates. These are more sensitive indicators of population health, and they enable us to identify the problems before they become irreversible.”
The study’s results indicate an immediate need for more effective population management strategies to protect the region’s dolphin population. Rather, recent trends point to negative growth rates, going below zero. That would be enough for a dramatic 2.9 percent population decline.
“There is an urgent need to manage the population better,” – Etienne Rouby.
He further emphasized the importance of taking action before it is too late. “As humans, we should make conscious decisions to protect the living and non-living things around us.”
Long-Term Concerns for Common Dolphins
For long-lived species like common dolphins, which produce only a few offspring throughout their lifetimes, significant population declines can jeopardize recovery efforts. Recent years’ downward trend has raised concerns over the future viability of dolphin populations.
Rouby warned that failure to address these issues could result in dire consequences. “Otherwise, there is a risk for decline and ultimately, extinction.”