Change the towing speed of 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 changing the towing speed of a trawl net on catch of marine fish. The study was in the North Sea (Norway). 





  • Improved size-selectivity of fishing gear (1 study): One replicated, paired study in the North Sea found that changing the towing speed of a bottom trawl net did not increase the size selectivity of small cod and haddock.

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 study in 1995 of one area of seabed in the North Sea off southern Norway (Dahm et al. 2002) found that changing the towing speed of a bottom trawl net did not improve the size selectivity of unwanted small cod Gadus morhua and haddock Melanogrammus aeglefinus. Across both vessels and net sizes, the length at which fish had a 50% chance of escaping was similar between two towing speed ranges for both cod (slower: 30–34 cm, faster: 30­–34 cm) and haddock (slower: 28–32, faster: 28–33). In April 1995, trawl towing speed was tested on two fishing vessels (20 deployments each), fishing at the same time on the same fishing grounds (exact location not reported). Vessels had different sizes of bottom trawl nets, one a standard size and one a scaled-down size but both had identical codends (see paper for specifications). For the larger net, catches were analysed for towing speeds above and below 3.0 m/s and for the smaller net <3.5 versus >3.5 m/s. Fish retained by the larger net were sampled in twin codends, one with the test net and one with a small mesh to sample all sizes of fish. On the smaller net a cover was attached to the codend to collect fish escaping through the meshes. All codend and cover catches were sorted and weighed by species and total lengths recorded.

    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

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Marine Fish Conservation

This Action forms part of the Action Synopsis:

Marine Fish Conservation
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