Abstract:To determine whether seismic exploration affected abundance or catch rates of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), acoustic mapping and fishing trials with trawls and longlines were conducted in the central Barents Sea 7 days before, 5 days during, and 5 days after seismic shooting with air guns. Seismic shooting severely affected fish distribution, local abundance, and catch rates in the entire investigation area of 40 × 40 nautical miles.Trawl catches of cod and haddock and longline catches of haddock declined on average by about 50% (by mass) after shooting started, which agreed with the acoustic abundance estimates; longline catches of cod were reduced by 21%. Reductions in catch rates were observed 18 nautical miles from the seismic shooting area (3 × 10 nautical miles), but the most pronounced reduction occurred within the shooting area, where trawl catches of both species and longline catches of haddock were reduced by about 70% and the longline catches of cod by 45%; a relatively greater reduction was found (in catches and acoustic estimates) for large (>60 cm) than for small fish. Abundance and catch rates did not return to preshooting levels during the 5-day period after seismic shooting ended.Résumé : Pour déterminer si l'exploration sismique nuit à l'abondance de la morue (Gadus morhua) et de l'églefin (Melanogrammus aeglefinus) ainsi qu'au taux de capture de ces espèces, on a procédé à des travaux de cartographie acoustique et à des essais de pêche au chalut et à la palangre dans la partie centrale de la mer de Barents 7 jours avant, 5 jours durant et 5 jours après une série de tirs sismiques au canon pneumatique. Les tirs ont considérablement modifié la répartition du poisson, abaissé sa densité locale et gravement réduit le taux de capture dans l'ensemble de la région d'étude (soit un secteur mesurant 40 milles marins de côté). En moyenne, les prises de morue et d'églefin au chalut et les prises d'églefin à la palangre ont diminué d'environ 50% (en masse) après que la série de tirs ait commencé. Ces résultats concordent avec ceux des relevés acoustiques d'abondance. Les prises de morues à la palangre ont été réduites de 21%. Des baisses des taux de prise ont été observées jusqu'à 18 milles marins du secteur des tirs sismiques (un secteur de 3 × 10 milles marins), mais l'effet le plus prononcé a été observé à l'intérieur de ce secteur : les prises au chalut des deux espèces et les prises à la palangre de l'églefin ont diminué d'environ 70%, les prises de morue à la palangre d'environ 45%. La réduction est proportionnellement plus marquée dans le cas des poissons de grande taille (>60 cm) que celle des poissons de petite taille, tant dans les prises que dans les estimations par relevé acoustique. Cinq jours après la fin des tirs sismiques, l'abondance et les taux de capture ne s'étaient pas encore rétablis. [Traduit par la Rédaction]

A full-scale fishing experiment on north-east Arctic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), involving a trawler, a longliner and a gillnetter was conducted in order to determine how the length distributions and life history parameters of the catches were affected by gear type. Relative selectivity was analysed for catches taken when the boats fished simultaneously in the same area, and when the skippers were allowed to fish under conditions as close as possible to commercial operation. Trawl and longline-caught cod had similar length distributions, but cod caught by trawl were on average 2.3 cm smaller than longline-caught cod. Cod caught by longline had a lower condition factor and length at age. The longliner caught smaller haddock than the trawler when the boats fished in the same area. When the skippers were allowed to change fishing ground, the mean length of cod increased in the trawl catches and became larger than the mean length in the longline catches. The mean length of haddock in the longline catches increased by 2.8 cm and became larger than that of the trawl catches. Gillnet catches consisted almost solely of large cod. Mean length of gillnet caught fish in 186 mm nets decreased from 86.2 cm to 82.3 cm even if the boat did not change area. Separate selectivity experiments for trawl and gillnet were conducted, and the parameters for the mesh selection are presented. To find the functional form of the longline selectivity we used relative catch proportion in each 5 cm length-group for longline compared to trawl and gillnet, whose selectivities were assumed to be known. When compared to that of the gillnet, the plots indicate that the longline selectivity curve takes the form of a unimodal distribution. When longline catches was compared to trawl catches none of the suggested models seemed to fit, and to conclude anything about the form of the longline selection curve is not possible. International Council for the Exploration of the Sea

Ingólfsson, Ó. A., Soldal, A. V., Huse, I., and Breen, M. 2007. Escape mortality of cod, saithe, and haddock in a Barents Sea trawl fishery. – ICES Journal of Marine Science, 64: 000–000. We investigated the survival of gadoid fish in the Barents Sea escaping from a demersal trawl during commercial fishing conditions, with and without a sorting grid, at high and low levels of fishing intensity. The mortality of cod and saithe was negligible and unrelated to experimental conditions. Haddock mortality was generally greater than observed in earlier experiments and inversely related to fish length. Any possible effects of experimental conditions were hidden by large variability in the observed rates of mortality. We conclude that the observed mortality of haddock is confounded by methodological problems, particularly the instability of the observation cages, and does not reflect the true escape mortality. Cod and saithe are capable of surviving the stress of passage through, and escape from, the trawl, whereas haddock are more vulnerable, despite being a closely related species.

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