Study

Confounding effects of knot orientation in penaeid trawls

  • Published source details Broadhurst M.K., Sterling D.J. & Millar R.B. (2016) Confounding effects of knot orientation in penaeid trawls. Fisheries Research, 179, 124-130

Actions

This study is summarised as evidence for the following.

Action Category

Modify the design or configuration of trawl gear (mixed measures)

Action Link
Marine Fish Conservation
  1. Modify the design or configuration of trawl gear (mixed measures)

    A replicated, paired, controlled study (year not provided) of sand and mud bottom in an estuary off the Tasman Sea, New South Wales, Australia (Broadhurst et al. 2016) found that modifying a prawn trawl net (knot orientation) reduced the catches of unwanted fish species compared to a conventional trawl. Overall catch rate of unwanted fish species was lower in a modified trawl with a negative knot angle of attack than the conventional positive attack angle (modified: 90 fish/ha, conventional: 110 fish/ha). For the five most abundant non-target fish species caught, individual catch rates were lower with negative angles of attack for three: yellowfin bream Acanthopagrus australis (modified: 4, conventional: 8 fish/ha), southern herring Herklotsichthys castelnaui (modified: 2, conventional: 8 fish/ha) and silver biddy Gerres subfasciatus (modified: 0.2, conventional: 1.3 fish/ha); but similar for forktail catfish Arius graeffei (modified: 80, conventional: 88 fish/ha) and Ramsey’s perchlet Ambassis marianus (modified: 0.4, conventional: 0.7 fish/ha). Target school prawn Metepenaeus macleayi catches were also lower with the modified knot orientation (modified: 675, conventional: 775 ind/ha). Fishing trials were done in the austral summer in the Clarence River estuary (2–20 m depth) using a local trawler. Knot-force direction in the top and bottom net panels was compared by turning a conventional trawl with a positive angle of attack inside out to create a negative angle of attack (see original paper for full gear specifications). A total of 24 paired deployments (45 min) of both trawl types were completed. The authors reported that altering the knot orientation may have affected the overall geometry of the trawl during fishing (e.g. a lower position in the water column and lower headline height).

    (Summarised by: Chris Barrett)

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