Sampling uncertainty associated with western Mediterranean pelagic fish abundance estimates derived from acoustic data.
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AuthorsTugores, M.P. (María Pilar); Miquel-Batle, J. (Joan); Oñate-Garcimartín, D. (Dolores); Díaz, N. (Nuria); Iglesias, M. (Magdalena)
Acoustic surveys are used worldwide for the assessment of pelagic fish stocks. In the Spanish Mediterranean area acoustic surveys are performed annually in late autumn and cover the entire continental shelf between 30 and 200 m depth. This survey was initiated to obtain estimates of anchovy recruitment (Engraulis encrasicolus), but additionally provide a general overview of the whole pelagic fish community in the study area during the time of the year it is performed. Our study area has a diverse assemblage of small and medium-sized pelagic fish (up to nine species) and thus we rely on the proportion of species obtained in middle-water pelagic fishing trawls to attribute the amount of echo corresponding to every single species and estimate their abundance. Although uncertainties may arise from many different sources (e.g. transducer motion, target strength, migration) we focus our study on the estimation of overall sampling uncertainty, one of the main contributors to random error. We ...