Thursday, June 20, 2019
Home World Acoustic repellents on boats to stop dolphin hecatombs

Acoustic repellents on boats to stop dolphin hecatombs

A guard from the National Wildlife Hunting Board takes the size of a dozen dolphins found stranded on a beach on the Atlantic coast. (Photo illustration). – MICHEL GANGNE / AFP

  • These massive strandings of dead dolphins, most of which are killed by being accidentally caught in fishing nets, have been observed since 1989 by the Pelagis Observatory. But the phenomenon has taken a worrying dimension since 2017.
  • Pointed the finger, the fishermen are in search of solutions. They have just generalized for pelagic trawlers – a priori most concerned by these strandings – pingers, acoustic repellents that help keep dolphins away from the nets.
  • Already experienced last summer, these pingers would reduce accidental bycatch by 65%. There is still room for improvement and alternative solutions for other fishing techniques.

It is a sad scene that is repeated all too often in recent years. Corpses of common dolphins are regularly deposited by the sea on the beaches of the French Atlantic coast.

The carcasses are very often mutilated. "They have the fins cut, deep sores that are the signs," says Hélène Peltier, research engineer at the Pelagis Observatory, (CNRS-University of La Rochelle), which monitors populations of marine mammals in the Atlantic. And when the corpses are sufficiently "fresh" to practice an autopsy, one often concludes a death by asphyxiation. So many signs that before arriving there, these dolphins got caught in fishing gear and died there. "

26 corpses found Tuesday in the north of Vendée

On the only day of Tuesday, with a colleague, the scientist found twenty-six on the Vendée coast, between Saint-Jean-de-Mont and
Talmont-Saint-Hilaire. "A fortnight was too damaged to make a diagnosis, the others were almost exclusively" classic "wounds. Other surveys were planned this Wednesday by Pelagis, in the same department after new reports. A little further south, Dominique Chevillon, president of the association
 Nature and environment re, expects to make, too, new macabre discoveries on the beaches of his island. "We've picked up 22 dead common dolphins just this Sunday," he said. They add to the eight already registered since the beginning of winter. In Gironde,
a hundred dolphins also failed on the altantic coast in one week.

The phenomenon is not new. Hélène Peltier dates back to 1989 the first massive beaching of common dolphins found in the Bay of Biscay [entre la Bretagne et le nord de l’Espagne]. But intensities vary from year to year. Sometimes there are only a few scattered strandings. And then, there are the dark years. These have been linked even since 2017 "That year, 900 strandings of common dolphins had been recorded in the Bay of Biscay, including 800 between February and March," reports the research engineer in Pélagis.

Accidental catch in fishing gear

Bar and hake fishing is singled out to explain this incidental catch. That in particular that practices pelagic trawls French beef and whose season extends from January to mid-March. This corresponds to the period when the Pélagis observatory notes the recrudescence of dolphin strandings.

This fishing technique involves two ships hauling in the open sea a closed funnel-shaped net to collect the coveted fish. France has nineteen pairs of pelagic trawls working in the Bay of Biscay. "The difficulty is that the bars and
hake that we fish feed on the same small fish (anchovies, sardines …) as these common dolphins ", explains Hubert Carré, general manager of
 National Committee of Maritime Fisheries. Everyone is in the same place. "

Scientists struggle to explain why these dolphins get caught in the cracks. "These fishing gear make a lot of noise and dolphins are very sensitive animals to stress, says Hélène Peltier. No doubt, even though they still have the ability to get out of the nets, they panic, try to come to the surface and die of cardiac arrest or asphyxiation. "

Acoustic repellents to ward off dolphins

The Maritime Fisheries Committee does not deny these incidental catches and accompanies the French fishermen mobilized to find a solution. A solution that could be called "pingers" by the name of these acoustic repellents that now equip French pelagic trawlers. "They are installed directly on the trawl and emit sounds that allow dolphins to detect the presence of fishing gear and move away, the sound is their unpleasant," says Hubert Carré.

Pingers, these acoustic repellents, now equip the 19 pairs of French pelagic trawlers.
Pingers, these acoustic repellents, now equip the 19 pairs of French pelagic trawlers. – / Photo The fishermen of Brittany

The device has been slow to put together. "We had to find the right frequency," says Perrine Ducloy, project manager at the Maritime Fisheries Committee. The one that dissuades the common dolphins from approaching without hurting their auditory systems or attracting, conversely, other cetaceans in the nets, each species having frequencies that attracts or repels it. "

The effectiveness of the "pingers" was tested on three pairs of trawlers between February and April 2018 out of a total of more than 220 fishing operations in the Bay of Biscay. Result? A significant reduction in incidental catches of around 65% for trawls equipped with "pingers". "This season, the 19 French pairs have volunteered to equip these" pingers "and also welcome independent observers to try to better understand these bycatch," said Hubert Carré.

Trawls, not only responsible

Nevertheless, strandings continue in recent weeks. "2019 leaves even on very bad bases," fears Dominique Chevillon. "Proof that it is necessary to increase the effectiveness of these" pingers ", begins Hélène Peltier. It is the subject of a European research program, in progress, which will aim to put a system of "pingers" still more efficient that will only be triggered at the entrance of the trawl and in the presence of the dolphin . "

Proof also that pelagic trawls are not the only ones responsible for the strandings of common dolphins on the coasts of the Bay of Biscay. "We are now also convinced that net fishing also generates bycatch," says the Pelagis scientist. The technique is not to tow a net but to deposit it in the bottom or let it drift between two waters before lifting it later. "It is likely that these nets act then as a physical barrier in which can take the common dolphins," continues Hélène Peltier.

These gillnet vessels have less fishing capacity than the trawlers, but they are much more numerous and their fishing season is longer. It will also be necessary to equip these boats with a solution against accidental catches of cetaceans. But Hélène Peltier and Perrine Ducloy agree on this point: equipping all nets with "pingers" is probably not the solution … at the risk of transforming the entire Bay of Biscay into hostile territory for common dolphins.


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