Comment épargner les juvéniles de soles et de gadidés dans la pêcherie crevettière : expériences de chalut sélectif en baie de Vilaine, première partie

The French brown shrimp (Crangon crangon) fishery employs on a seasonal basis around 140 ships about 10 metres in length and with engines of about 100 kilowatts of power. It takes place mainly along the coastal bottoms of silted-up sand at a depth of 2 to 10 metres and occupies principally the coasts of the eastern English Channel and those of the Gulf of Gascony. The brown shrimp catch is performed by bottom trawl, with exempted meshing of 20 mm (stretched mesh), which causes numerous rejects of immature fish that live on the same bottoms. The main part of these juveniles is made up of flat fish (sole, in particular) and of gadidae (whiting and pout). To reduce these undesirable catches that are also detrimental to other fisheries, some ingenious fishermen developed selective trawls. Two types of selective trawls have existed in France for some twenty years: the Asselin trawl and the Devismes trawl. But these trawls are not used by all brown shrimp fishermen, because some judge them to be too complicated. In 1994, IFREMER was petitioned by the professional fishermen of Vilaine Bay (maritime district of Vannes) to study the problems of selectivity and, consequently, to save a maximum of juvenile fish. IFREMER of Lorient was tasked with conducting the necessary investigations. A preliminary study made it possible to know how the Asselin and Devismes trawls performed, which made it possible to save about half of the juveniles brought into the trawl, without any notable loss of brown shrimp (DUPOUY and VACHEROT, 1994). IFREMER therefore recommended using either of these trawls while waiting to study the possibilities of perhaps improving the selectivity. In 1996, most of the shrimp boats of the Vannes district and the neighbouring district of Saint-Nazaire had a selective trawl. Financing, obtained from the Regional Council of Morbihan by means of the Local Committee of Auray-Vannes Fisheries, made it possible to pursue the study on the selectivity of the trawls.