Fit mesh escape panels/windows to a trawl net and use square mesh instead of diamond mesh codend
Overall effectiveness category Awaiting assessment
Number of studies: 1
Background information and definitions
Mesh escape panels (or windows) in commercial trawl nets are sections of net inserted in the codend or extension piece of a different mesh size and/or orientation (i.e. square) to the rest of the codend. They were developed to provide an area of escape for some fish while retaining target species such as prawns/shrimps that are expected to pass underneath. Square mesh codends provide another area for selection in a trawl net and may allow the escape of smaller fish. Square meshes, as opposed to conventional diamond meshes, are more likely to stay open under tension during trawling and thus create a larger gap through which fish can more easily pass. Thus, the combination of a mesh panel and square mesh codend should allow a larger number and range of individuals to escape from a trawl net than a conventional diamond mesh codend, or one or other of the escape panel or square mesh codend alone. However, likelihood of escape may depend on the species being targeted and the fish assemblages in the area being fished.
The effects of using just mesh panels or just a square mesh codend are summarized under ‘Fishing gear modification - Fit mesh panels/windows to a trawl net’ and ‘Use a square mesh instead of a diamond mesh codend in a trawl net’, respectively. Similar interventions of various combinations of unwanted catch reduction devices, including mesh panels and square mesh codends are summarized under ‘Fishing gear modification’.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2007 of two fished areas of seabed in the English Channel off southwest England, UK (Wade et al. 2009) found that beam trawl nets with two square mesh escape panels (top and bottom) and a square mesh codend, reduced discarded fish catch compared to a standard diamond mesh codend with no escape panels. Across both sampling areas, the modified nets with escape panels and square mesh codends caught 54–63% fewer discarded finfish (617–770 fish) than standard diamond mesh codends (1,652–1,685 fish). Total numbers of six of the nine most numerous fish species/groups were reduced in one or both areas by 17–95%, while there were no differences for three species/groups. In addition, modified nets reduced the retained finfish catches in one of two areas by 22% (modified: 558 fish, standard: 718 fish). Catch comparison trials were done at two separate bottom fishing grounds off the south west coast of England by two commercial beam trawl vessels in July and August 2007. A total of 16 deployments were made of two beam trawl nets towed simultaneously: one modified with two 200 mm square mesh panels (upper and lower) and a 80 mm square mesh codend; and a standard 80 mm diamond mesh codend with no square mesh panels (see paper for specifications). Catches from both trawl nets were kept separate and divided into discarded and retained portions. Discarded finfish and all retained fish were identified, and their total lengths measured (sub-sampled where necessary).Study and other actions tested