how Drix, the underwater drone, tries to unravel the reasons for accidental captures of dolphins

It has been almost a month since they no longer had the right to fish: the trawlers in the Bay of Biscay will be able to return to sea. The fishing ban which had affected 450 vessels since January 22 was lifted on Tuesday February 20.

This unprecedented measure, imposed by the Council of State, was intended to protect dolphins, accidentally captured in nets, along the Atlantic coasts. It must be renewed next year. In the meantime, scientists are trying to understand why so many dolphins get caught in nets and how to fix it. Among their tools is Drix, a marine drone which completed a week of observation in the open sea on Sunday February 18.

“Detecting dolphin sound emissions”

Moored among the sailboats of Noirmoutier, in Vendée, it stands out with its appearance of a red submarine, eight meters long and packed with sensors essential for scientists, like Mathieu Doray: “The sensors are located in the keel which is two meters deep. We have a hydrophone which allows us to detect the sound emissions of common dolphins. And an echo sounder is a type of sonar which allows us to detect prey such as sardines, anchovies, mackerel, etc.

For a week, these instruments scanned the depths between Royan and Noirmoutier. An area where accidental captures of dolphins are the most important: “We had a little gust of wind offshore, a strong swell, 3.50 meters, and the drone did very well.” And when Drix is ​​at sea, the Ifremer researcher is cozy in his office in Nantes. With a mystery to solve: why since 2016, catches have increased so much, reaching up to 10,000 last year? “One of the hypotheses, explains Mathieu Doray, This is because the dolphins would have moved closer to the coasts of the Bay of Biscay, because there would be more interesting prey for them, typically anchovies.”

“Prey very close to the bottom”

To verify this hypothesis, scientists analyze recordings: “What we observed at certain times in winter and which was really new, was a very dense carpet of fish which led us to suppose that the accidental captures of dolphins could be due to the presence of prey very close to the bottom.”

“Instead of closing the entire Bay of Biscay, let’s try to target areas where the risk is greatest”

Matthew Doray

at franceinfo

So much information that could help adapt fishing bans: “We could close these areas for longer, to really limit the risks, while leaving other areas open. This is the whole challenge of the research we are currently carrying out”specifies the researcher.

It now remains for scientists to evaluate the number of dolphins that were able to be saved thanks to this first ban measure. The research project called Delmoges must continue for another year.