Study

Effects of catch size and codend type on the escapement of walleye pollock (Theragra chalcogramma) from pelagic trawls

  • Published source details Erickson D.L., Perez-Comas J.A., Pikitch E.K. & Wallace J.R. (1996) Effects of catch size and codend type on the escapement of walleye pollock (Theragra chalcogramma) from pelagic trawls. Fisheries Research, 28, 179-196

Actions

This study is summarised as evidence for the following.

Action Category

Fit mesh escape panels/windows to a trawl net

Action Link
Marine Fish Conservation

Use a larger mesh size

Action Link
Marine Fish Conservation
  1. Fit mesh escape panels/windows to a trawl net

    A replicated, randomized, paired, controlled study in 1994 of pelagic fishing sites in the Bering Sea off Alaska, USA (Erickson et al. 1996) found that fitting square mesh escape panels to pelagic trawl nets reduced the amount of undersized walleye pollack Theragra chalcogramma in small but not large catches, compared to standard all-diamond mesh codends. The percentage catch of pollock smaller than 36 cm was lower in codends with square mesh panels than without, at catch sizes below 40 tonnes in weight (with: 6–15%, without: 20–46%) but was similar at catches of 40 tonnes and above (with: 19–25%, without: 18–25%). In July–August 1994, codends fitted with a top panel of square mesh of two different mesh sizes (95 mm and 108 mm) were compared with a standard codend diamond mesh codend of 85 mm (see paper for specifications). Commercial deployments of individual codends were done in a randomized block design, in daylight hours for a maximum duration of four h. Data were collected for each type of codend from seven to eight tows of catches below 40 tonnes and 3–10 tows above 40 tonnes. Codend catches were transferred from four catcher vessels to a factory trawler where sorting and sampling of pollack took place.

    (Summarised by: Khatija Alliji)

  2. Use a larger mesh size

    A replicated, randomized, controlled study in 1994 of an area of midwater in the Bering Sea, Alaska, USA (Erickson et al. 1996) found that trawl codends of larger mesh size reduced the catches of undersized walleye pollack Theragra chalcogramma at smaller catch sizes but not larger, compared to a conventional smaller mesh codend. Data were reported as percentage catch composition. In catches <40 tonnes, the average percentage of undersized (<36 cm) pollock caught was lower with both larger mesh codends: a 88 mm mesh (88 mm: 17%, standard: 38%) and a 113 mm mesh (113 mm: 7%, standard: 24%), compared to a standard smaller mesh codend. However, in catches ≥ 40 tonnes the percentage of undersized pollack was similar in all codends (30–45%). Between July and August 1994, trawling using different codend types (including different mesh material and codends with square mesh panels of different sizes – see paper for data) was conducted during daylight hours (maximum duration of four hours) off Unimak Island. A total of 60 deployments were completed by four vessels in a randomized block design with sequential tows using either one of two experimental codends (113 mm and 88 mm diamond mesh) and a standard diamond mesh codend (85 mm inside layer) that was double-layered with the effect of having a smaller mesh than the experimental nets. All catches were sorted and counted.

    (Summarised by: Khatija Alliji)

Output references

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