Study

Effects of bycatch reduction devices in Queensland's (Australia) deepwater eastern king prawn (Melicertus plebejus) trawl fishery

  • Published source details Courtney A.J., Campbell M.J., Tonks M.L., Roy D.P., Gaddes S.W., Haddy J.A., Kyne P.M., Mayer D.G. & Chilcott K.E. (2014) Effects of bycatch reduction devices in Queensland's (Australia) deepwater eastern king prawn (Melicertus plebejus) trawl fishery. Fisheries Research, 157, 113-123.

Actions

This study is summarised as evidence for the following.

Action Category

Fit a size-sorting escape grid (rigid or flexible) to trawl nets and use a square mesh instead of a diamond mesh codend

Action Link
Marine Fish Conservation

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

Action Link
Marine Fish Conservation

Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

Action Link
Marine Fish Conservation
  1. Fit a size-sorting escape grid (rigid or flexible) to trawl nets and use a square mesh instead of a diamond mesh codend

    A replicated, randomized, paired, controlled study in 2002 of a coastal seabed site in the Coral Sea, Australia (Courtney et al. 2014) found that prawn trawl nets fitted with a size-sorting escape grid (a turtle excluder device) and a square mesh codend reduced the catches of the most frequently caught unwanted fish species, but not of less frequently caught species compared to a standard diamond mesh codend, and overall fish catch rates were similar to a square mesh codend alone. For seven of eight unwanted fish species caught in 26–85% of tows, average catch rates were lower in nets with a grid and square mesh codend (with: 0–93 g/ha, standard: 6–134 g/ha) and were similar for one species (with: 7 g/ha, standard: 5 g/ha). For a further 18 unwanted fish species caught in 6–31% of tows, there were no differences in average catch rates between grid/square mesh codend nets and standard nets (with: 0–43 g/ha, without: 1–27 g/ha). In addition, the catch rates of most unwanted fish (24 of 26 species) were similar to a square mesh codend without a grid (see paper for individual data). Catch rates of the target eastern king prawns Melicertus plebejus were similar between all net types (grid/square mesh codend: 264, square mesh codend: 267, standard: 274 g/ha). In July 2002, data were collected from 65 paired trawl deployments done over 10 nights off the coast of Queensland. Three different codends were tested against a standard diamond mesh codend: a standard diamond mesh with a metal, top-opening grid (Wick’s turtle excluder device), the grid in combination with a square mesh codend, and a square mesh codend alone (see paper for specifications). Each codend design was randomly assigned to the two trawl nets every 12 tows. Each tow was 2 nm long, at 2.2 knots.

    (Summarised by: Khatija Alliji)

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

    A replicated, randomized, paired, controlled study in 2002 of a fished area of seabed in the Coral Sea, Australia (Courtney et al. 2014) found that a prawn trawl net with a square mesh codend reduced the overall amount of unwanted non-target catch (fish and invertebrates) compared to a conventional diamond mesh trawl, and the effect on individual fish species varied. Average catch rates by weight of total unwanted catch (fish and invertebrates, seven fish species accounting for 50% by weight) was lower in square mesh compared to diamond mesh codends, both with and without grids (square: 796–908 g/ha, diamond mesh: 1,114–1,150 g/ha). By individual fish species, five of the 40 species analysed had lower catch rates (three by over 90%) in square mesh than diamond mesh codends, without grids (square: 1–115 g/ha, diamond: 5–134 g/ha), one was higher (square: 29 g/ha, diamond: 60 g/ha) and there were no differences between codend types for the rest (see paper for spceis individual data). Over 10 days in July 2002, data were collected from 65 paired trawl deployments on deepwater eastern king prawn fishing grounds off the southeast Queensland coast. Four codends were tested: a 48 mm square mesh with and without a rigid escape grid (turtle excluder device), and a 45 mm diamond mesh codend with and without a grid. Codend designs were randomly assigned to one of the two outer trawl nets of a triple-rigged trawl every 12 hauls and towed simultaneously.

    (Summarised by: Khatija Alliji)

  3. Fit a size-sorting escape grid (rigid or flexible) to a prawn/shrimp trawl net

    A replicated, paired, controlled study in 2002 of a coastal seabed area in the Coral Sea, Australia (Courtney et al. 2014) found that prawn trawl nets fitted with a rigid size-sorting escape grid (turtle excluder device) did not reduce the amount of unwanted fish catch, compared to a standard diamond mesh trawl codend. For one of 26 unwanted fish species with data (see paper for list of species), the average catch rate was lower with a grid than without (with: 94.7 g/h, without: 134.3 g/h) but for the remaining, average catch rates were either similar (23 species) or higher (two species) between nets (with: 1.3–95.7 g/ha, without: 1.1–72.2 g/ha). In addition, catch rates of the target eastern king prawns Melicertus plebejus were similar between nets (with: 291.1–274.4 g/ha). In July 2002, data were collected from 65 paired trawl deployments done over ten nights off the coast of Queensland. Three different codends were tested against a standard diamond mesh codend: a standard diamond mesh with a metal, top-opening grid (Wick’s turtle excluder device), a grid in combination with a square mesh codend, and a square mesh codend alone (see paper for specifications). Each codend design was randomly assigned to the two trawl nets every 12 tows. Each tow was two nm long, at 2.2 knots.

    (Summarised by: Khatija Alliji)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 18

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust