Fit one or more soft, semi-rigid, or rigid grids or frames and increase the mesh size of pots and traps
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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, a device such as a rigid frame or rigid wires can be fitted to the entrance of the trap or elsewhere on the trap, to reduce the likelihood of large unwanted species entering, but also to allow small unwanted species to escape once inside the traps (Broadhurst et al. 2014). In combination with this frame, 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” and “Increase the mesh size of 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
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 fitted with escape frames and designed with larger mesh size, compared to conventional traps. The proportion of undersized crabs caught in traps fitted with frames and designed with 101 mm mesh appeared lower (11%) compared to conventional traps without frames and of 51 mm mesh (29%; results not tested for statistical significance). In addition, the number of wounded mud crabs (undersized and commercial size) was statistically similar in traps with escape frames and larger mesh size (0.04 crabs/trap) and conventional traps (0.13 crabs/trap). Conventional traps have four 300 × 200 mm funnel entrances, no escape frames, and are designed with 51 mm mesh. Conventional traps were modified by fitting two 46 × 120 mm escape frames and 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