Study

Reducing the benthos by-catch in flatfish beam trawling by means of technical modifications.

  • Published source details Fonteyne R. & Polet H. (2002) Reducing the benthos by-catch in flatfish beam trawling by means of technical modifications.. Fisheries Research, 55, 219-230.

Actions

This study is summarised as evidence for the following.

Action Category

Fit one or more mesh escape panels/windows to trawl nets

Action Link
Subtidal Benthic Invertebrate Conservation
  1. Fit one or more mesh escape panels/windows to trawl nets

    A replicated, paired, controlled study in 1999 in two soft seabed areas in the southern North Sea, Belgium and Thames estuary, UK (Fonteyne & Polet 2002a) found that a modified trawl net with either diamond or square mesh escape zones (“bycatch reduction device”) did not reduce the amount of unwanted invertebrate catch overall compared to a standard unmodified net, and had mixed effects on the catch of individual species. The overall weight of unwanted invertebrates caught was not significantly different from standard nets for the nets with diamond mesh escape zones (diamond: 91; standard: 103 kg) or square mesh escape zones (square: 137; standard: 142 kg). Of the 11 unwanted invertebrate species caught, nets with diamond mesh escape zones reduced the catch of one, increased the catch of two, and caught similar amounts of the remaining eight, compared to standard nets. Nets with square mesh escape zones caught similar amounts of all species. Both designs of escape zones caught similar amounts for five of the six commercial species caught and reduced the catch of one species (plaice Pleuronectes platessa) by 15–18%. The escape zone (large diamond or large square mesh; 400 mm) were fitted to a beam trawl net (4 m) behind the ground rope. Fishing took place simultaneously with one modified and one standard unmodified net by attaching the two nets to an 8 m beam. Hauls (10 for diamond mesh; 6 for square mesh) were conducted in March 1999 in 20–50 m water depth. Total catch weights were recorded, and all invertebrate species were separated, weighed and identified to species level.

    A replicated, controlled study in 1999–2000 in two soft seabed areas in the southern North Sea, Belgium and Thames estuary, UK (Fonteyne & Polet 2002b) found that overall when fitted to trawl nets, square mesh windows ( “bycatch reduction device”) of three different sizes reduced unwanted catch of invertebrates, compared to nets without a device, and had mixed effects on the catch of individual species. The windows decreased the overall weight of unwanted invertebrates caught by 64–83% compared to unmodified nets. The 120 mm window significantly decreased catches of six of 16 species (45–95% reduction). The 150 mm window significantly decreased catches of 11 of 17 species (34–90% reduction). The 200 mm window significantly decreased catches of four of 16 species (92–97% reduction). The 120 mm window increased the catch of one of eight commercially targeted species (by 111%) compared to nets without a device, with no differences for the remaining seven. The 150 mm window did not impact the catch of any commercially targeted species. The 200 mm window decreased catches of two of eight commercially targeted species (by 23–45%) compared to nets without a device, with no differences for the remaining six. Windows of either 120 mm, 150 mm or 200 mm mesh size were fitted to a beam trawl net (4 m) just in front of the codend. Nets were deployed between November and February 2000 at 20–50 m depth during paired hauls (one net with and one without a device; 5–16 hauls/window type; by attaching the two nets to one 8 m beam). All unwanted invertebrates were identified, counted, and weighed. Commercial catches were identified and weighed. No comparisons were made between windows of different mesh sizes.

    (Summarised by: Anaëlle Lemasson & Laura Pettit)

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