||Mesure in-situ de l'indice de cible acoustique d'anchois (Engraulis encrasicolus) et de sardines (Sardina Pilchardus) européens, avec observations vidéo simultanée
||Doray Mathieu, Berger Laurent, Coail Jean-Yves, Vacherot Jean-Philippe, Bavouzet Gerard, Petitgas Pierre
||International Council for the Exploration of the Sea Annual Science Conference, 19-23 septembre 2011, Gdansk
||ICES Conference and Meeting (CM) Document CM2011-F07 19-23 septembre 2011, Gdansk
||The lack of specific Target Strength (TS) values for European anchovy (Engraulis encrasicolus) and sardine (Sardina Pilchardus) in the literature has been pointed out by the Working Group on Acoustic and Egg Surveys for Sardine and Anchovy in ICES Areas VIII and IX. The need for specific small pelagics TS measurements conducted in controlled environments was recognized by the group, to further investigate the adequacy of TS length equation used to derive fish stock estimates for clupeids in European waters. TS is a stochastic variable which largely varies in the wild, in response to changes in physical (tilt angle, depth) or biological (physiology) single fish attributes. The first requirement to make sound TS measurement is to accurately identify of the species comprising fish targets. Fish target identification is usually carried out by fishing. The comparison between fishing and acoustic data may be biased by the large differences in sampling volume and selectivity between acoustic and fishing devices. Optical systems can improve target identification, by providing images of the fish simultaneously insonified by the echosounder. We used Ifremer’s towed body ‘EROC’, fitted with an optical-acoustic system, to conduct in-situ TS measurements of Biscay anchovy and sardine, with concurrent optical identification. Its combination with an “open” pelagic trawl termed “ENROL” allowed for the recording of small pelagic fish TS, while controlling for the prominent factors known to influence fish TS distribution: species, length and tilt angle. Repeating EROC/ENROL-based TS measurements on monospecific schools should then allow for the definition of accurate TS~length equations for near horizontal small European pelagic fish species.