INDEXES OF BLUEFIN TUNA (THUNNUS-THYNNUS-THYNNUS) ABUNDANCE DERIVED FROM SALE RECORDS OF FRENCH PURSE SEINE CATCHES IN THE MEDITERRANEAN SEA

Sampling operations are not routinely conducted in France to monitor t he landings of bluefin tuna caught by purse seiners in the Mediterrane an. The length, weight and age frequencies of bluefin caught by this f leet are predicted based on sale records, length-at-age and weight-len gth relations, trends in fishing and natural mortality rates, and othe r ancillary data. The resulting length frequencies are more accurate t han those predicted by Liorzou and Bigot (1992) using a simpler algori thm, and are spread more evenly across adjacent size classes. Catch-pe r-unil-effort (CPUE) was expressed as the numbers of age 2 bluefin cau ght per successful seine fishing trip in the Gulf of Lions fall fisher y. CPUE indices were computed by several methods, and compared to that of the spanish baitboat fishery in the Bay of Biscay. The index trend s of the french and spanish fleets exhibit a general increase during 1 970-95, but the results do not demonstrate which of these is the best indicator of juvenile abundance. Complementary surveys are required to determine the temporal and spatial distributions of surface schools a nd fishing effort, and identify the most reliable index of abundance.