Study

Selectivity of square mesh codends of pelagic trawls for Atlantic mackerel (Scomber scombrus L.)

  • Published source details Casey J., Nicholson M.D. & Warnes S. (1992) Selectivity of square mesh codends of pelagic trawls for Atlantic mackerel (Scomber scombrus L.). Fisheries Research, 13, 267-279.

Actions

This study is summarised as evidence for the following.

Action Category

Use a square mesh instead of a diamond mesh codend in a trawl net

Action Link
Marine Fish Conservation

Use a larger mesh size

Action Link
Marine Fish Conservation
  1. Use a square mesh instead of a diamond mesh codend in a trawl net

    A replicated, paired, controlled study in 1990 in an area of pelagic water in the western English Channel, UK (Casey et al. 1992) found no difference in the size composition (selection) of Atlantic mackerel Scomber scombrus in catches from a pelagic trawl with a large square mesh codend, compared to a smaller diamond-mesh codend. Length frequencies of mackerel caught with a 60 mm square mesh codend (range: 8–31 cm, midpoint: 13 cm) were similar to a 40 mm diamond mesh codend (range: 7–32 cm, midpoint: 13 cm). In January–February 1990, mackerel catches were compared from 14 trawl deployments on a commercial fishing vessel: nine with an experimental square mesh codend (60 mm); and five with a conventional diamond mesh codend (40 mm). The experimental codend was 4 m shorter than the conventional codend and had four net panels instead of two. Each trawl type was deployed alternately when mackerel shoals were visible in the water, and all mackerel caught were counted and their lengths measured.

    (Summarised by: Leo Clarke)

  2. Use a larger mesh size

    A controlled study in 1990 of an area of midwater in the western English Channel, UK (Casey et al. 1992) found that a pelagic trawl net with a square mesh codend of larger mesh size caught similar sizes of Atlantic mackerel Scomber scombrus compared to a conventional smaller sized diamond mesh codend, and thus there was no difference in size-selectivity. The length frequencies of mackerel caught were similar between a 60 mm square mesh codend (range: 8-31 cm, midpoint: 13 cm) and a 40 mm diamond mesh codend (range: 7-32 cm, midpoint: 13 cm). In January–February 1990, a total of 14 trawl deployments were undertaken in the western English Channel from a 64 m commercial fishing vessel. Nine trawl deployments used an experimental codend of 60 mm square mesh, and five deployments used a conventional 40 mm diamond mesh codend. The experimental codend was 4 m shorter than the conventional codend, with four panels rather than the conventional two. Each trawl design was deployed alternately when shoals of mackerel were visible in the water. All mackerel caught in each trawl were counted and measured.

    (Summarised by: Leo Clarke)

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