Estimating gear efficiency in a combined acoustic and trawl survey, with reference to the spatial distribution of demersal fish

Type Article
Date 2010-05
Language English
Author(s) Doray MathieuORCID1, Mahevas Stephanie1, Trenkel VerenaORCID1
Affiliation(s) 1 : IFREMER, EMH, F-44311 Nantes 03, France.
Source Ices Journal Of Marine Science (1054-3139) (Oxford Univ Press), 2010-05 , Vol. 67 , N. 4 , P. 668-676
DOI 10.1093/icesjms/fsp277
WOS© Times Cited 14
Keyword(s) availability, Bay of Biscay, catchability, generalized linear model, geostatistics, hake, vulnerability
Abstract Few analyses have been performed to estimate the efficiency of trawls targeting demersal fish using the ratio of catches and acoustic densities. In summer 2006, acoustic and fishing data were collected simultaneously over 3 d by three fishing vessels equipped with identical pelagic trawls in the Bay of Biscay. Variography identified moderate spatial autocorrelation in the acoustic backscatter at a mean scale of 3 km, a scale slightly smaller than the mean haul length (3.5 km), indicating that fish horizontal availability did not influence trawl efficiency. Acoustic backscattering densities expressed as nautical area scattering coefficients (NASCs) recorded in the trawled layer were compared with equivalent NASC (ENASC) values calculated from the species composition in the trawl, fish-length structure, and available relationships between target strength and fish length. Estimates of trawl efficiency for hake-dominated trawls were computed as the slopes of the relationships ENASC = 0.008 NASC and ENASC = 0.18 NASC0.31 for trawls made by day and night, respectively. For the whole demersal community, the relationships were ENASC = 0.022 NASC and ENASC = 0.17 NASC0.33 for trawls made by day and night, respectively.
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