Fit a funnel (such as a sievenet) or other escape devices on shrimp/prawn 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 inserting a funnel-like device (such as a sievenet) before the codend (Santos et al. 2018). This device is designed to direct unwanted catch to an escape hole in the body of the trawl. The idea is that the target species go over the hole in the net, while non-target species can escape through the release hole. These funnel-like devices are usually not made of rigid material and therefore can be more acceptable to fishers than a rigid sorting grid (evidence summarised under “Threat: Biological resource use – Fit one or more soft, semi-rigid, or rigid grids or frames to trawl nets”).
Santos J., Herrmann B., Mieske B., Krag L. A., Haase S. & Stepputtis D. (2018) The efficiency of sieve‐panels for bycatch separation in Nephrops trawls. Fisheries Management and Ecology, 25, 464–473.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2006–2007 in the North Sea, off the east coast of England, UK (Catchpole et al. 2008) found that trawl nets used in shrimp/prawn fisheries fitted with a sievenet (funnel-like device) appeared to catch fewer unwanted non-commercial invertebrates (discard) compared to unmodified nets. Differences were not statistically tested. Of the seven invertebrate discard species recorded, six tended to be caught in lower numbers in nets fitted with a sievenet compared to nets without (28–83% reduction in numbers caught), and one species tended to be caught in equal numbers. Use of selective gear to reduce unwanted catch in the brown shrimp fishery was made compulsory in 2003 in the European Union. Between January 2006 and January 2007, abundances of unwanted invertebrate species were compared in nets with a sievenet and without. Nets were deployed in pairs (one sievenet; one unmodified net) during 98 hauls for 1h. All organisms were identified, sorted as commercial catch or discard, and counted.Study and other actions tested