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Nathalie Reti Nathalie Reti

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Nathalie Retière Laboratoire d'Écologie J. Massé Biscay. Hauls piecharts which indicate the species compositions in corresponding catches. integration units between different combinations pelagic hauls the short prospecting time the study area data were both day-time. Six different systematic- sampling estimates were calculated from using two, three, four or eight transects and their corresponding hauls The biomass different combinations their respective variation were calculated using the trawl samples for allocating the echo-integration values to the species. According to Diner (1983) compositions were previously weighted by the density observed at the fishing location this objective, weighting factor calculated for each haul and catch proportion for species in haul and Simmonds, 1992) calculated from the acoustic target strength Combinations of systematic-sampling estimates horse mackerel (Vorobyov Ivanov, 1981) mackerel (Edwards and species (Gadidae) 32, 31, 38, 32, was calculated each species and each Aquat. Living Resour., Acoustic biomass the respective the acoustic energy observed at the fishing location. was calculated each combination, the acoustic energy at the fishing location. estimates for each species is the area (square nautical miles) and energy (acoustic units) observed variance is calculated the ratio (Cochran, 1977) acoustic energy observed m the at the coefficient of variation derived from the the variance estimators reflects heterogeneity of the species an area are based on the density observed by acoustics. AND DISCUSSION Combination of transects acoustic energy total biomass the number of transects acoustic units, and the calculated biomasses per species significantly from combination to another (anchovy from 968 to tons; sardine from on identification hauls. 3 and 6 give similar results, indicating that the number great effect on the estimate. On the other hand, combinations 5 (3 different results. that the distributed throughout the contrary, hauls are located and east the study and had very different species compositions, anchovy compared distributions, combination higher anchovy biomass the difference biomass estimates we that the coefficient of variation increased the number hauls decreased acoustic energy (acoustic abundance index for each hauls and transects. the abundance 2 for each species Abundance indices calculated when systematically removing table) and when considering Average, standard deviation variations are on the eight estimates with missing haul. Anchovy Sprat 119 288 126 304 132 290 fluctuations from species to another, less pronounced for the The position the identification hauls seems greater effect on the by species the contribution an area, biomass estimates have calculated using only the biomass calculations. that one haul significant variations. mackerel, sardine a factor On another hand, anchovy are more stable, ranging t to horse mackerel results are this species poorly represented species like mackerel and sardine which are usually aggregated big shoals, in water column and characterised fishing gears this area at and temporal scales shows that an increase in the number of transects accuracy of global biomass estimate. hand, if species compositions from samples are split the biomass into species number of indices by acoustics, concerned, which stress the need their location previous catchability studies. Nevertheless, this study identification hauls biomass estimates by species the acoustic seems to lively species This research the Commission of the European Communities the framework EEC research to thank particularly who greatly manuscript and Scalabrin for Anonymous 1983. Report of the 1983 planning group on sprat acoustic G. 1977. Sampling techniques. John New York, ARL scanner. 1983. Évaluation acoustique des stocks poissons pélagiques la partie du golfe Coudeville 1990. acoustic data acquisition processing system. congrès français d'acoustique, avril 1990. Zakkaria, eds. Paris, suppl. C2, 939-942. target strength and mackerel. 1980. Importance in acoustic a comparison gadoid and mackerel 1993. Identification spatial stratification acoustic populations. acoustic estimating Massé J. 1988. Utilisation halieutique (analyse des campagnes effectuées dans le golfe de Gascogne de 1987). Rapp. IFREMER, DRV-88030, 155 Leggett 1988. Hydroacoustics signal C., J. 1993. Acoustic the spatial and temporal distribution the Bay Living Resour. M., A. Ivanov 1981. the single the echo survey. Meeting on methods for the estimations populations, Cambridge, June 1979, Suomala ed. Weill A., C. 1993. MOVIESB: acoustic detection description software. Application shoal species Living Resour.