Fit one or more mesh escape panels/windows and one or more soft, rigid or semi-rigid grids or frames to trawl nets
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Trawling is a method of fishing that involves pulling a cone-shaped fishing net (trawl) through the water behind one or more boats. The net is wide at the opening and narrows to a bag or ‘codend’, tied at the end with a drawstring, where organisms are trapped. Trawl nets can catch a considerable number of unwanted organisms, including non-commercially targeted species and organisms under the legal-size limit. To reduce the amount of unwanted organisms, a net can be modified by fitting one or more mesh “escape panels” in the outer mesh of the net before the codend in combination with one or more “grids” to the inner side of the net before the codend (Brewer et al. 2006). The grid is designed to prevent them entering the net and/or codend (Brčić et al. 2015) and the mesh panels are designed to allow them to escape the net (Revill & Jennings 2005). Mesh panels, which can also be referred to as escape windows, escape zones, and drop-out panels, or more generally as “bycatch reduction devices”, can be fitted directly before the codend, or elsewhere on the main body of the net such as behind the groundrope. Here, we included escape zones such as “Bigeye” and “Fisheye” devices, as although they do not strictly use mesh sections, they have similar functions of letting organisms escape through a specific area of the net.
Evidence related to the use of each modification (mesh panels and grids) separately, are summarised under “Threat: Biological resource use – Fit one or more mesh escape panels/windows to trawl nets” and “Fit one or more soft, rigid or semi-rigid grids or frames to trawl nets”.
Brewer D., Heales D., Milton D., Dell Q., Fry G., Venables B. & Jones P. (2006) The impact of turtle excluder devices and bycatch reduction devices on diverse tropical marine communities in Australia's northern prawn trawl fishery. Fisheries Research, 81, 176–188.
Brčić J., Herrmann B., De Carlo F. & Sala A. (2015) Selective characteristics of a shark-excluding grid device in a Mediterranean trawl. Fisheries Research, 172, 352–360.
Revill A.S. & Jennings S. (2005) The capacity of benthos release panels to reduce the impacts of beam trawls on benthic communities. Fisheries Research, 75, 73–85.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2001 in areas of seabed in the Gulf of Carpentaria, northern Australia (Brewer et al. 2006) found that nets fitted with a mesh escape window (“bycatch reduction device”) and a grid (“turtle excluder device”), caught fewer large sponges and reduced the total weight of small unwanted catch (invertebrates and fish combined), compared to unmodified nets. Nets fitted with both escape window and grid caught 85% fewer large sponges and reduced the weight of small unwanted catch by 8%, compared to unmodified nets. The modified nets reduced the catch of commercially targeted prawns by 6%. The use of a “turtle excluder device” and a “bycatch reduction device” has been compulsory since 2000 in the Australian prawn fishery. Commercial vessels towed twin Florida Flyer prawn trawl nets from each side of the vessels in August–November 2001. Modified nets were fitted with both one of two designs of escape window (a “Bigeye” design or a square-mesh escape window) and one of 23 grid designs (rigid or semi-rigid frame with ≤120 mm bar spacing and an opening of ≥700 mm). A modified and an unmodified net were randomly assigned to either side of the vessel and towed simultaneously (324 modified nets examined for small unwanted catch, 150 for sponges; 703 unmodified nets for small unwanted catch, 339 for sponges). Total weights of small unwanted catch (<300 mm), commercially targeted prawns, and counts of sponges (>300 mm) were recorded. The combinations of various device designs were not compared. The “Bigeye” design was later removed from the Australian list of approved escape zone designs.Study and other actions tested