Les pêcheries françaises du chalutage à bar : analyse de séries temporelles 1999-2007

A displacement of the fishing effort of the French pelagic trawlers from anchovy to the seabass fisheries is observed. A such situation on a non-quota managed species requires to analyse carefully the evolution in the status of seabass stocks. The evolution of fishing effort, the production and the landings per unit of effort were studied from 2000 to 2007 for the bottom trawling and for the pair pelagic trawling in the ICES sub-areas VIII and VII. The fishing effort was assessed by using a threshold on the landings by month in order to select the most effective fishing effort as representing 75 % of the effort concerned with seabass landings. Length compositions and age-length keys were used to calculate the cpue-at-age series. A total mortality value was assessed from the annual abundance index of each year class. An increase of the fishing effort of pelagic trawling was detected in the English Channel area since 2005. Concomitantly, good recruitments (1999, 2000 and 2001 year classes) were observed in that area which could have stimulated the displacement of effort from anchovy towards seabass. These good year classes have also limited the negative impact of the fishing effort on the durability of the exploitation. The abundance in the English Channel in 2007 appears similar to the situation in 2003. A total mortality coefficient was assessed equal to 0.438 for combined areas VII &VIII. This mortality estimate results from all the fishing components on the [7-11] years old fish and it includes also the impact of the recreational fisheries. A relationship between total length and the circumference of the body was established for seabass of the English Channel - Celtic Sea areas. Such model is useful to determine the mesh to be used for adequacy with the minimum landing size. For instance, to catch only fish greater than 42 cm long, a stretched mesh size of 114 mm needs to be used; and the catch of animals of at least 8 years could be achieved with a 140 mm stretched mesh size. The analysis which provides useful information on the evolution of the status of stocks requires to be updated as soon as possible.