Use netting of contrasting colour in a trawl net

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • One study examined the effect of using netting of contrasting colour in a trawl net on marine fish populations. The study was in the Baltic Sea (Denmark). 





  • Reduction of unwanted catch (1 study): One replicated, paired, controlled study in the Baltic Sea found that a trawl codend with contrasting black netting used in conjunction with a square mesh escape panel caught a similar amount of undersized cod as a conventional codend.
  • Improved size-selectivity of fishing gear (1 study): One replicated, paired, controlled study in the Baltic Sea found that two designs of contrasting netting colour in trawl codends with square mesh escape windows did not improve the size-selectivity of cod compared to conventional codend netting colour.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A replicated, paired, controlled study in 1995–1996 of bottom fishing grounds in the Baltic Sea, Denmark (Madsen et al. 1998) found that contrasting black netting used in conjunction with a square mesh window in a trawl net codend (three designs) did not reduce catches of undersized Atlantic cod Gadus morhua in one case, and did not improve size-selectivity in two cases, compared to trawls with conventional codends of green netting. In a trial of one of three black netting designs, catch numbers of undersized (<35 cm) cod were similar compared to the conventional green (black: 2,030 fish, conventional: 2,184 fish; size-selectivity not calculated). In a separate trial of two other black netting designs, the length at which cod had a 50% chance of escape was similar in one case (32.1 vs 32.7 cm) and smaller in the other (28.2 vs 33.4 cm) compared to the conventional netting. The corresponding numbers of undersized cod caught in these two designs of modified codends compared to the conventional was 746 vs 881 fish, and 672 vs 335 fish, respectively (no statistical result reported). In total, 30 experimental deployments were made in August 1995 and February 1996 around Bornholm, using twin trawls. One trawl was fitted with a green netting codend modified with sections of contrasting black netting (three different designs) to improve fish escape through a square mesh panel, and one with a conventional green codend. Both trawls were fitted with a square mesh panel (compulsory since 1995). Deployments were 175–280 min at 2.7–3.4 knots. Small mesh covers were installed over each codends to collect the escaping fish. Full details of codend designs are provided in the original paper.

    Study and other actions tested
Please cite as:

Taylor, N., Clarke, L.J., Alliji, K., Barrett, C., McIntyre, R., Smith, R.K., and Sutherland, W.J. (2021) Marine Fish Conservation: Global Evidence for the Effects of Selected Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Marine Fish Conservation

This Action forms part of the Action Synopsis:

Marine Fish Conservation
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 21

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 ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust