SCALLOP (PECTEN-MAXIMUS) POPULATION-DYNAM ICS IN THE BAY OF BREST - WAS YESTERDAY DIFFERENT FROM TODAY

The project to renew the scallop stock in the Bay of Brest requires th at the possible effect of human activities on the health of the popula tion be first addressed. We shall try to do this here, by analysing hi storical data on the production of this fishery, and by comparing the characteristics of this scallop fishery in the past with those prevail ing recently. Year to year variation in catch, fishing effort and catc h per unit effort (cpue), as well as in recruitment (derived from the frequency in the 5 to 6 cm size class), are described for the 1950s. T he cpue fluctuated around a mean with a decreasing trend, interpreted as indicating overfishing relative to the recruitment, and in which ye ar-class abundance depends on each year's recruitment. This explanatio n is corroborated by the demonstration of a positive relationship betw een annual variation in cpue and that of the abundance in the size cla sses from 5 to 6 cm and from 7 to 8 cm. From the Second World War unti l the 1970s, the dynamics of the system comprised by the stock and the fishery, has manifested a succession of oscillations around equilibri a interrupted by two major events: the general motorization of the fis hing fleet in 1953, and massive mortality during the exceptionally col d winter of 1962/63. In the 1950s, the fishing pressure is estimated a t 20 % of stock biomass, mortality due to both fishing and natural cau ses thus exceeding the mean recruitment rate, in the range 3 to 20 %. The recent state of the stock is estimated by an assesment study carri ed out in October 1994. Apart from a much lower stock level, no notabl e change in fishing pressure or recruitment rate could be discerned, r elative to those during past times. The consequences for stock repopul ation are discussed in relation to this low recruitment rate, which is regulated by the physical characteristics of the environment.