Study

Reducing the discards of finfish and benthic invertebrates of UK beam trawlers.

  • Published source details Wade O., Revill A.S., Grant A. & Sharp M. (2009) Reducing the discards of finfish and benthic invertebrates of UK beam trawlers.. Fisheries Research, 97, 140-147.

Actions

This study is summarised as evidence for the following.

Action Category

Fit mesh escape panels/windows to a trawl net and use square mesh instead of diamond mesh codend

Action Link
Marine Fish Conservation

Fit one or more mesh escape panels/windows to trawl nets and use a square mesh instead of a diamond mesh codend

Action Link
Subtidal Benthic Invertebrate Conservation

Use a square mesh instead of a diamond mesh codend on trawl nets

Action Link
Subtidal Benthic Invertebrate Conservation

Use a square mesh instead of a diamond mesh codend in a trawl net

Action Link
Marine Fish Conservation
  1. Fit mesh escape panels/windows to a trawl net and use square mesh instead of diamond mesh codend

    A replicated, paired, controlled study in 2007 of two fished areas of seabed in the English Channel off southwest England, UK (Wade et al. 2009) found that beam trawl nets with two square mesh escape panels (top and bottom) and a square mesh codend, reduced discarded fish catch compared to a standard diamond mesh codend with no escape panels. Across both sampling areas, the modified nets with escape panels and square mesh codends caught 54–63% fewer discarded finfish (617–770 fish) than standard diamond mesh codends (1,652–1,685 fish). Total numbers of six of the nine most numerous fish species/groups were reduced in one or both areas by 17–95%, while there were no differences for three species/groups. In addition, modified nets reduced the retained finfish catches in one of two areas by 22% (modified: 558 fish, standard: 718 fish). Catch comparison trials were done at two separate bottom fishing grounds off the south west coast of England by two commercial beam trawl vessels in July and August 2007. A total of 16 deployments were made of two beam trawl nets towed simultaneously: one modified with two 200 mm square mesh panels (upper and lower) and a 80 mm square mesh codend; and a standard 80 mm diamond mesh codend with no square mesh panels (see paper for specifications). Catches from both trawl nets were kept separate and divided into discarded and retained portions. Discarded finfish and all retained fish were identified, and their total lengths measured (sub-sampled where necessary).

    (Summarised by: Chris Barrett)

  2. Fit one or more mesh escape panels/windows to trawl nets and use a square mesh instead of a diamond mesh codend

    A replicated, paired, controlled study in 2007 in two areas of the English Channel, southwest England, UK (Wade et al. 2009) found that fishing with a trawl net fitted with a square mesh codend and two large square mesh release panels (“bycatch reduction devices”) reduced the biomass of non-commercial unwanted invertebrate catch (discard) compared to a standard trawl. Across the two areas, the modified trawls caught 39–45% less invertebrate discard (349–730 kg) compared to the standard trawls (635–1,207 kg). However, they caught 22–82% fewer commercial shellfish (94–101 individuals), compared to standard trawls (120–570 individuals). The modified trawls also caught 22% less commercially important fish in one area, but those were worth more per kg than the fish caught in the standard trawls. Two designs of trawl nets were towed simultaneously: a modified beam trawl with an 80 mm square mesh codend and fitted with two large 200 mm square mesh release panels (one to release weed and one to release invertebrates), and the industry standard beam trawl with an 80 mm diamond mesh codend. Seven to nine tows/area were conducted in July–August 2007. The catch was sorted into commercially important species (target and non-target commercial catch) and discard species. Commercial organisms were counted, and discards were further sorted into benthic invertebrates and finfish and each were weighed.

    (Summarised by: Anaëlle Lemasson & Laura Pettit)

  3. Use a square mesh instead of a diamond mesh codend on trawl nets

    A replicated, paired, controlled study in 2007 in two areas of the English Channel, southwest England, UK (Wade et al. 2009) found that in one of two areas a trawl net fitted with a square mesh codend caught less non-commercial unwanted invertebrates (discard) compared to a standard trawl fitted with a diamond mesh codend. In one of two areas examined, using a square mesh codend instead of a standard diamond mesh codend reduced the biomass of invertebrate discard by 11% (square: 794 vs diamond: 889 kg). The square mesh codend caught similar amounts of commercially targeted species (megrim and anglerfish in that area) to the standard trawl and caught 26% more commercially important shellfish. In the other area, the square mesh codend caught similar biomass of invertebrate discard (1,746 kg) as the diamond mesh codend (1,842 kg), and similar amounts of commercially targeted species (Dover sole and plaice in that area). Two designs of trawl nets were towed simultaneously: a modified beam trawl with an 80 mm square mesh codend, and the industry standard beam trawl with an 80 mm diamond mesh codend. Twelve tows/area were conducted in July–August 2007. The catch was sorted into commercially important species (target and commercial unwanted catch) and discard species. Commercial organisms were counted, and discards were further sorted into benthic invertebrates and finfish and each were weighed.

    (Summarised by: Anaëlle Lemasson)

  4. Use a square mesh instead of a diamond mesh codend in a trawl net

    A replicated, paired, controlled study in 2007 of two fished areas of seabed in the English Channel off southwest England, UK (Wade et al. 2009) found that beam trawl nets with square instead of diamond mesh codends, reduced the amount of discarded finfish catch. Across both sampling areas, the square mesh codends caught 30–52% fewer discarded finfish than the diamond (square: 1,496–1,830 fish, diamond: 2,124–3,836 fish). By individual fish species/groups, total numbers of four (all roundfish) of the nine most numerous were reduced in one or both areas by 18–80%, while for the rest (all flatfish), there were no differences between codend types for four and one was lower (by 56%) in the square mesh in the inshore area only. In addition, the retained finfish catches were similar between codend types in both areas (square: 943–985 fish, diamond: 948–1,005 fish). Catch comparison trials were done at two separate bottom fishing grounds off the south west coast of England by two commercial beam trawl vessels during 6 d sampling trips in July and August 2007. A total of 24 deployments were made of two beam trawl nets towed simultaneously: one an 80 mm square mesh codend, and one a standard 80 mm diamond mesh codend (see paper for specifications). Catches from both trawl nets were kept separate and divided into discarded and retained portions. Discarded finfish and all retained fish were identified, and their total lengths measured (sub-sampled where necessary).

    (Summarised by: Chris Barrett)

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