Danish experiments with a grid system tested in the North Sea shrimp fishery

  • Published source details Madsen N. & Hansen K.E. (2001) Danish experiments with a grid system tested in the North Sea shrimp fishery. Fisheries Research, 52, 203-216.


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, paired, controlled study of a seabed area in the North Sea, between Scotland and Norway (Madsen & Hansen 2001) found that fitting a flexible size-sorting escape grid in a shrimp trawl net typically reduced the catches of undersized cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangus and the overall numbers of Norway pout Trisopterus esmarki and saithe Pollachius virens but not monkfish Lophius piscatorius, compared to trawl nets without an escape grid. In two of two trials, total catch numbers of undersized fish were lower in nets with grids for cod (with: 365–382, without: 1,237–1,805) and haddock (with: 253–579, without: 4,617–5,315). Numbers of undersized whiting were lower in one (with: 15, without: 123) of two (with: 9, without: 11) trials. Overall catch numbers were reduced by 40–55% for Norway pout (two of two trials) and 73% for saithe (one of two trials). Monkfish catch numbers were similar between nets for two of two trials (with: 40–67, without: 43–66). Trials were conducted in the Fladen Ground shrimp fishery onboard a commercial twin-trawler in April–May (20 hauls) and August (30 hauls). A codend fitted with an escape grid was deployed on one side of the gear simultaneously with a standard codend on the other side. A collecting bag caught fish escaping through the grid. The flexible (polyamide) grid was 12 mm diameter bars of 19 mm spacing, fitted at 48° angle, with a fish escape hole at the top and a Norway lobster Nephrops norvegicus escape hole at the bottom (see paper for grid specifications). A panel of square mesh netting to retain marketable sizes of roundfish was fitted to the top of the net behind the grid. Fish from the codend and collecting bag were sorted separately into species and lengths recorded. The study year was not reported.

    (Summarised by: Chris Barrett)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust