Modify design or arrangement of tickler chains/chain mats in a bottom trawl

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

Study locations

Key messages

  • Two studies examined the effects of modifying the design or arrangement of tickler chains in a bottom trawl on marine fish populations. One was in the North Sea (Netherlands/UK) and one was in the Atlantic Ocean (Scotland). 





  • Reduction of unwanted catch (2 studies): One of two replicated, paired, controlled studies in the North Sea and Atlantic Ocean found that removing the tickler chain from a trawl reduced catches of non-commercial target skates/rays and sharks, and individuals were larger, compared to trawling with the chain. The study also found that catches of commercial target species were typically unaffected. The other study found that two modified tickler chain arrangements did not reduce discarded fish catch compared to a standard arrangement.

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 1999 on bottom fishing grounds in the North Sea between the Netherlands and UK (van Marlen et al. 2005) found that two different modifications to the way tickler chains were attached to a beam trawl (hanging parallel from, or in loops along, the beam) did not reduce the discarded fish catch, compared to a conventional tickler chain arrangement. For unwanted fish (undersized commercial target species and all other non-target species), there were no differences in catches between the modified and conventional tickler chain arrangements, except for small whiting Merlangius merlangus, of which fewer were caught by the modified gear (data not reported). Data were collected from a series of beam trawl deployments along six parallel strips on the seabed (2,000 m × 30 m) using two modified and one conventional tickler chain arrangement. In March-April 1999, a total of 72 deployments were carried out with three different configurations of parallel chains (numbers and spacing, connected pairs) hung along the beam. In October 1999, a total of 35 deployments were undertaken with three configurations of chains hung in loops from the beam. In addition, a standard trawl with conventional tickler chain arrangement (attached to the shoe plates on either end of the beam) was towed simultaneously during each deployment. All catch was weighed.

    Study and other actions tested
  2. A replicated, paired, controlled study in 2005 in an area of seabed in deep water in the Atlantic Ocean off the Isle of Skye, Scotland, UK (Kynoch et al. 2015) found that removal of the tickler chain from a bottom trawl reduced the capture of unwanted skates/rays (Batoidea) and unwanted sharks (Chondrichthyes) compared to a standard trawl with a tickler chain. Overall, trawl gear without a tickler chain decreased the catch of skates/rays (four species) and sharks (three species) compared to a trawl with a tickler chain (skates/rays, without: 198 individuals, with: 625 individuals; sharks, without: 993 individuals, with: 1,357 individuals). For the more commercially valuable species, overall catch rates of three flatfish species (Pleuronectidae) and two cod-like species (Gadidae) were similar between trawls, however, catch rates of two anglerfish Lophius sp. decreased with a tickler chain (see paper for data). Trials took place onboard a commercial fishing vessel in October 2005. A total of 17 paired deployments of standard bottom fish trawls, one with the tickler chain removed, were made, parallel to one another, at 120–170 m depth.

    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?

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Marine Fish Conservation

This Action forms part of the Action Synopsis:

Marine Fish Conservation
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