Statistical aspects of trials of a separator trawl using a twin rig trawler

  • Published source details Cotter A.J.R., Boon T.W. & Brown C.G. (1997) Statistical aspects of trials of a separator trawl using a twin rig trawler. Fisheries Research, 29, 25-32.


This study is summarised as evidence for the following.

Action Category

Use a separator trawl

Action Link
Marine Fish Conservation
  1. Use a separator trawl

    A replicated, randomized study in 1994 in two areas of seabed in the North Sea, UK (Cotter et al. 1997) found that using a separator trawl separated the majority of unwanted Atlantic cod Gadus morhua into a lower trawl net from other target fish species that were retained in an upper trawl net, and size-selectivity in the lower trawl net increased with increasing mesh size. Across five trawl deployments, the probability of cod entering the lower codend was 0.87 (min: 0.74, max: 0.96). The length at which cod had a 50% chance of escape was 33.8 cm in the lower codend with a 100 mm mesh size (min: 26.2, max: 53.1 cm) and 57.6 cm in the lower codend with a 140 mm mesh size (min: 42.5, max: 80.1 cm). Results were not tested for statistical significance. Five experimental trawl deployments were undertaken with a separator trawl off Whitby, northeast England in March 1994 and in the Moray Firth, Scotland in November 1994. The trawl was a standard trawl divided horizontally by a panel behind the footrope into two codends. The upper codend had 100 mm mesh size and two randomly assigned lower codends had 100 mm or 140 mm mesh size. Full details of trawl design are provided in the original study.

    (Summarised by: Leo Clarke)

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