Total selectivity of a commercial cod trawl with and without a grid mounted: grid and codend selectivity of north-east Artic cod

Kvamme, Cecilie; Isaksen, Bjørnar

doi:10.1016/j.fishres.2003.11.011

Cited by 26 publications

(34 citation statements)

References 24 publications

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“…If it is the objective of managers to minimise capture of juveniles while maintaining catches of legal sized sh, the selective device with the smallest SR is preferable, because it, with a proper choice of L 50 , meets this objective. The analysis of our data, supported by the results of Kvamme and Isaksen (2004), indicate that in this respect there is no signi cant di erence between grids and traditional diamond mesh codends. Moreover, modelling of the stock e ects of changes in eet selectivity has shown changes in SR to have smaller impact on long-term yield than a change in L 50 (Kvamme and Frøysa, 2004).…”

Section: Discussionsupporting

confidence: 76%

“…The SR was approximately 1 cm narrower when the grid was installed. Kvamme and Isaksen (2004) observed that L 50 for cod increased by approximately 4 cm with the inclusion of a 55 mm Sort-X grid in the Barents Sea cod shery, with no e ect on selection range. The reduced catch of juveniles observed when shing with a grid installed, may thus be the result of a higher mean selection length of grids compared to the codend mesh size used and not caused by narrower selection range of grids.…”

Section: Introductionmentioning

confidence: 93%

“…The inclusion of subsampling fractions as an o set is equivalent to the binomial model for data obtained from retrospective sampling (McCullagh and Nelder, 1989), introduced for selectivity analysis by Millar (1994). For the combined grid-and mesh selectivity, the total selection of the gear was better described by modelling the combined selection of grid and codend meshes by a single logistic function, rather than as a product of two logistic curves (Kvamme and Isaksen, 2004). The product model is more complex, with higher number of parameters and gives worse t (higher deviance).…”

Section: Statistical Analysesmentioning

confidence: 99%

“…Estimates were based on pooled data, and the parameters were obtained from selection curves tted by eye. The Norwegian data set was subsequently re-estimated by Kvamme and Isaksen (2004), giving L 50 and SR of 47.1 and 13.4 cm respectively. Unfortunately the Russian data was not available for re-examination, but the estimates were closer to recently obtained data (Kvamme and Isaksen, 2004).…”

Section: Introductionmentioning

confidence: 99%

“…The Norwegian data set was subsequently re-estimated by Kvamme and Isaksen (2004), giving L 50 and SR of 47.1 and 13.4 cm respectively. Unfortunately the Russian data was not available for re-examination, but the estimates were closer to recently obtained data (Kvamme and Isaksen, 2004). Only a few studies have determined the combined selectivity of grids and codends (Anon, 1998).…”

Section: Introductionmentioning

confidence: 99%

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Size selection of cod by rigid grids—Is anything gained compared to diamond mesh codends only?

et al. 2006

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Size selective grids were introduced into the Barents Sea demersal trawl shery in 1997. It was believed at the time that in comparison to standard diamond mesh codends, grids had better selective properties, i.e. narrower selection range. Few studies have directly compared the selective properties of the combined grid and codend with that of the codend only. In this study we describe two experiments carried out in 2002 and 2003, where we directly compared the properties of codend selectivity for cod (Gadus morhua ) with the combined selectivity of a Sort-V grid and a codend. In 2002 we used small-meshed covers, whereas the twin trawl method was used in 2003. In both experiments we compared the selectivity of a 135 mm codend only with that of a trawl tted with a 135 mm codend and a 55 mm grid, which is the mandatory con guration. In 2003 we also estimated the selectivity of a 155 mm diamond mesh codend, having an L 50 similar to that of the grid and 135 mm codend combination. The results presented no evidence that the grid and mesh combination had sharper size selection than codend meshes. The introduction of the mandatory use of grid in the shery in 1997 therefore only increased L 50 , and corresponded to a mesh size increase of around 20 mm. Mean selection length of the grid was inversely related to catch rates in the 2002 experiment when large catches were taken. Grid selection appeared less a ected by seasonal variations in degree of stomach fullness or condition than mesh selectivity. Other situations where grid selection might perform better than mesh selection are discussed.

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Section: Discussionsupporting

confidence: 76%

Section: Introductionmentioning

confidence: 93%