Study

Effects of Turtle Excluder Devices on bycatch and discard reduction in the demersal fisheries of Mediterranean Sea

  • Published source details Sala A., Lucchetti A. & Affronte M. (2011) Effects of Turtle Excluder Devices on bycatch and discard reduction in the demersal fisheries of Mediterranean Sea. Aquatic Living Resources, 24, 183-192.

Actions

This study is summarised as evidence for the following.

Action Category

Install exclusion and escape devices on fishing gear

Action Link
Reptile Conservation

Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net

Action Link
Marine Fish Conservation
  1. Install exclusion and escape devices on fishing gear

    A replicated study in 2008 on the sea bottom in the Adriatic Sea (Sala et al. 2011) found that adding a downward-facing grid and bottom escape hole (‘Super Shooter’ model of ‘turtle excluder device’) to standard trawl nets allowed a loggerhead turtle Caretta caretta to escape after being caught. No statistical tests were carried out for unwanted catch. During trials, one turtle entered a trawl net modified with a ‘Super Shooter’ and was successfully excluded. No turtles entered trawl nets modified with two other excluder devices that were tested. The ‘Super Shooter’ retained the most catch (20 kg/tow) and had the lowest discards (9 kg/tow) of commercially-targeted European hake Merluccius merluccius, compared to the two other excluder devices that were tested (retention rate: 13–18 kg/tow; discard rate: 12–21 kg/tow). All turtle excluder devices were downward-facing grids (set to an angle of 45–48 degrees) located immediately in front of the codend and accompanied by a bottom escape hole. Four different excluder devices were tested: a lightweight rigid aluminium grid (which broke down and was excluded from the study); a flexible mixed-cable grid; a semi-rigid grid of steel and rubber; a ‘Super Shooter’ aluminium grid with enlarged space between bars (see original paper for details). Data were collected during 42 tows with an average duration of 48 minutes (11–15 tows/excluder device). Excluder devices were tested on a four-sided net using standard commercial trawl fishing rigging and operation.

    (Summarised by: Katie Sainsbury)

  2. Fit a size-sorting escape grid (rigid or flexible) to a fish trawl net

    A replicated study in 2008 of three bottom trawling sites in the North Adriatic Sea, Italy (Sala et al. 2011) found that fish trawl nets fitted with size-sorting escape grids (Turtle excluder devices) typically reduced the amounts of discarded fish catch and overall discarded catch (fish and invertebrates combined), relative to the codend catch. For three of three designs, grids reduced the average catch rates of nine of 12 discarded fish species (see paper for list of species) compared to the total catch that would have been retained if no grids were fitted (with: 0.17–1.27 kg/tow, without: 0.34–2.45 kg/tow), and for three of 12 fish species average catch rates were similar (with: 0.58–1.16 kg/tow, without: 0.58–1.50 kg/tow). Average catches of all discarded catch (fish and invertebrates) were reduced in nets with grids (with: 9–21 kg/tow, without: 25–28 kg/tow). Three different grid designs (flexible, rigid and semi-rigid construction), all with bottom escape openings, were tested in standard fish trawls used in Mediterranean bottom fisheries (see paper for specifications). Catch data was collected from 42 fishing deployments (11–15 per grid) in March 2008. Fish and marine invertebrates escaping through the grid were collected in a cover attached over the grid outlet. Cover and codend catches were pooled to calculate total catch of a ‘control’ net without a grid.

    (Summarised by: Khatija Alliji)

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