Reduction of fish by-catch in shrimp trawl using a rigid separator grid in the aft belly

  • Published source details Isaksen B., Valdemarsen J.W., Larsen R.B. & Karlsen L. (1992) Reduction of fish by-catch in shrimp trawl using a rigid separator grid in the aft belly. Fisheries Research, 13, 335-352.


This study is summarised as evidence for the following.

Action Category

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

Action Link
Marine Fish Conservation
  1. Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

    A replicated study in 1989–1990 of shrimp fishing grounds in the Northeast Atlantic, Norway (Isaksen et al. 1992) reported that shrimp trawl nets fitted with rigid size-sorting escape grids allowed small unwanted fish and Greenland shark Somniosus microcephalus to escape capture and escape frequency of the small fish increased with fish length. Data were not statistically tested. Trawl nets fitted with an escape grid released more Atlantic cod Gadus morhua and haddock Melanogrammus aeglefinus than were retained in the codend and all individuals larger than 20 cm (data were presented as length frequency distributions). For redfish Sebastes spp. higher proportions of fish >13 cm escaped than were retained and all redfish >18 cm. For polar cod Boreogadus saida higher proportions >14 cm escaped and all were released from 22 cm. All flatfish (including Greenland halibut Reinhardtius hippoglossoides and long rough dab Hippoglossoides platessoides) >30–32 cm escaped capture, although this larger size compared to other species was due to the species’ swimming behaviour. It was also reported that with a grid of at least 1.0 × 1.5 m, Greenland shark up to 4 m escaped relatively easily. In addition, target shrimp Pandalus borealis escapes were 2–5%. In 1989–1990, experimental deployments (location and number not reported) were undertaken using trawl nets fitted with an aluminium (Nordmøre) grid mounted at a 48° angle and top escape outlet. Covers mounted over the outlet collected the escaping fish. Two grid designs were used: a coastal (1.35 × 0.7–0.8 m) and an offshore (1.5 × 1.0–1.3 m) grid for smaller and larger vessels respectively. A remote-controlled underwater vehicle monitored fish behaviour. Data from the two grids were combined. Details of study location were not reported.

    (Summarised by: Leo Clarke)

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