Effect of catch size and shape on the selectivity of diamond mesh cod-ends II. Theoretical study of haddock selection

摘要

A series of computer simulations were carried out to predict how the selectivity of haddock in a diamond mesh cod-end varies according to total catch, by-catch, entry time of by-catch and the shape of the catch build-up in the cod-end. Results, were compared to those from sea trials. I also investigated the predicted selectivity on the assumption that the shape of the cod-end does not change as the catch accumulates. The latter investigations were carried out for various shapes of the cod-end. The simulations indicated that the 50% retention length (L50) increases with both the total catch and the by-catch weight They also indicated that the entry time of the by-catch may have an important influence on both the 50% retention length and selection range (SR). The shape of the catch in the cod-end had a similar effect, for the cases analyzed. Different cod-end shapes showed very large differences in the values for L50 as well as more narrow SRs. assuming that the shape of the cod-end remained constant during the tow. The simulations strongly indicate that the change of shape, of the diamond mesh cod-end as the catch builds Lip during towing is a major contribution to the SR. Copyright 2004 Elsevier B.V. All rights reserved.