Increase the mesh size of pots and traps

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

61%
Certainty

29%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Traps or pots are static gears often used to fish for crabs or lobsters. They consist of structures into which species of commercial interest enter through funnels. These funnels encourage entry but limit escape, and often catch a large amount of unwanted species (Stevens 1996). To try to minimise the amount of unwanted catch from this type of fishing, the size of the mesh used to construct the pots/traps can be increased, to increase the likelihood of unwanted species or smaller/younger individuals of the economically targeted species escaping (Broadhurst et al. 2014). This may potentially help reduce unwanted catch of subtidal benthic invertebrate species and benefit their populations.

Evidence related to the use of other “bycatch reduction devices” on pots and traps are summarised under “Threat: Biological resource use – Fit one or more soft, semi-rigid, or rigid grids or frames on pots and traps”.

_{Broadhurst M.K., Butcher P.A. & Cullis B.R. (2014) Effects of mesh size and escape gaps on discarding in an Australian giant mud crab (Scylla serrata) trap fishery. PloS One, 9, e106414.}

_{Stevens B.G. (1996) Crab bycatch in pot fisheries. Solving bycatch: considerations for today and tomorrow, 151–158}

Study locations

Key messages

One study examined the effects of increasing the mesh size of pots and traps on subtidal benthic invertebrates. The study took place in the Corindi River system (Australia).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Unwanted catch abundance (1 study): One replicated, controlled study in the Corindi River system found that traps designed with larger mesh appeared to reduce the proportion of unwanted undersized mud crabs caught, compared to conventional traps of smaller mesh.

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, controlled study (date unspecified but appears to be 2012) in a muddy and sandy area in the Corindi River system, eastern Australia (Broadhurst et al. 2014) found that traps used to catch giant mud crabs Scylla serrata appeared to catch fewer unwanted undersized mud crabs when designed with larger mesh size, compared to conventional traps. The proportion of undersized crabs caught in traps with 101 mm mesh appeared lower (22%) compared to conventional traps with 51 mm mesh (29%; results not tested for statistical significance). In addition, the number of wounded mud crabs (undersized and commercial size) was statistically lower in traps with larger mesh size (0.03 crabs/trap) compared to conventional traps (0.13 crabs/trap). Conventional traps are designed with 51 mm mesh. Conventional traps were modified by increasing the mesh size to 101 mm. Seven modified traps and seven conventional traps were tested during 20 deployments. All traps were baited with sea mullet Mugil cephalus. Traps were recovered after 24 hours, and all catch identified, counted, and any wounds assessed.
Study and other actions tested
Referenced paper
Kennelly S. & Broadhurst M. (2014) Mitigating the bycatch of giant cuttlefish Sepia apama and blue swimmer crabs Portunus armatus in an Australian penaeid-trawl fishery. Endangered Species Research, 26, 161-166.

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
Use a larger mesh size on trammel nets Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Fit one or more soft, semi-rigid, or rigid grids or frames to trawl nets Action Link	Likely to be beneficial	2	Synopsis Link
Use a pulse trawl instead of a beam trawl Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link