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
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How is the evidence assessed?

Effectiveness

65%
Certainty

20%
Harms

0%

Calculating overall effectiveness category

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.}

Study locations

Key messages

One study examined the effects of fitting a funnel, sievenet, or other escape devices on trawl nets on marine subtidal invertebrate. The study was in the North Sea (UK).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Unwanted catch abundance (1 study): One replicated, paired, controlled study in the North Sea found that trawl nets fitted with a sievenet appeared to catch fewer unwanted catch of non-commercial invertebrates compared to unmodified nets.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

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
Referenced paper
Catchpole T.L., Revill A.S., Innes J. & Pascoe S. (2008) Evaluating the efficacy of technical measures: a case study of selection device legislation in the UK Crangon crangon (brown shrimp) fishery. ICES Journal of Marine Science, 65, 267-275.

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K. & Sutherland, W.J. (2020) Subtidal Benthic Invertebrate Conservation. Pages 635-732 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Subtidal Benthic Invertebrate Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Set unwanted catch quotas Action Link	No evidence found (no assessment)	0	Synopsis Link
Use a square mesh instead of a diamond mesh codend on trawl nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Fit one or more mesh escape panels/windows and one or more soft, rigid or semi-rigid grids or frames to trawl nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link