Les pêcheries de Congre (Conger conger L.) dans le Mor Braz, Bretagne Sud (Eléments de la biologie et de gestion de la ressource)

When an important oxygen defficit occurred in the bottom waters of the Vilaine bay during 1982 summer, a great mortality rate of conger eels pointed the failures of our knowledge about the biology and of the ways of exploitation of this stock. This study tries to improve our data about these two topics. Counting of the otoliths rings is relevant for age determination. The length frequencies inside age groups 5 to 11, show two groups with different mean sizes. These two populations are understood as a growth difference between sexes. Females reach 2 metres, but males only 1. The catches sex-ratio point out that the female ratio is more important than the male one. This means changes into distribution area by sexes, with females in shallow waters. The increase of the Conger eel catches by French fishing vessels and specially by ships of southern Brittany, is important. Three gears are involved in the exploitation of this stock (lines, trawls and pots). But line is the most important with 80 percent in numbers. The age composition of the catches and the exploitation pattern show that ages 7 to 12 take charge of the greatest part of fishing effort. The yield per recruit results change hardly with the choise of natural mortality rate. But, maximum sustainable yield seems not to he attained, as showed by yearly standardized measures of relative abundance based on daily catches of liners.