A simulation-based attempt to quantify the morphological component of size selection of Nephrops norvegicus in trawl codends

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Abstract

The selectivity for Nephrops (Nephrops norvegicus) in trawl codends generally is poor and the lack of steepness of the selection curve results in high discard rates and/or loss of legal-sized catch. This poor codend selectivity often is attributed to the irregular shape of Nephrops, which to some extent characterizes the problem as insoluble. In the present study, the FISHSELECT methodology was used to examine the selection process of the species in order to identify ways to improve selectivity. The use of three different modes of orientation for contact (contact modes) with the codend meshes explained most of the characteristics of the selection curves for Nephrops obtained experimentally. The contact mode with the smallest cross-section was optimal for mesh penetration and, when evaluated against experimental data, 87.5% of all Nephrops encountering the gear were estimated to meet the netting in this contact mode. The range of configurations of the meshes (e.g., opening angles in the diamond mesh netting) was determinative for the selectivity, and the selective process for Nephrops was found to take place along the entire length of the codend. Simulating selectivity in a diamond mesh codend in which the closed meshes in the forward part of the codend were replaced by more open meshes revealed that the selectivity for Nephrops can be efficiently improved. (C) 2009 Elsevier B.V. All rights reserved.
Original languageEnglish
JournalFisheries Research
Volume101
Issue number3
Pages (from-to)156-167
ISSN0165-7836
DOIs
Publication statusPublished - 2010

Keywords

  • Trawl
  • Norway lobster
  • Morphology
  • Nephrops norvegicus
  • Selectivity
  • FISHSELECT

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