Action: Fit one or more soft, semi-rigid, or rigid grids or frames on pots and traps
Key messagesRead our guidance on Key messages before continuing
- One study examined the effects of fitting one or more soft, semi-rigid, or rigid grids or frames on 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 fitted with escape frames appeared to reduce the proportion of unwanted undersized mud crabs caught, compared to conventional traps without escape frames.
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 other types of “excluder devices” can be used, to reduce the likelihood of unwanted species entering, but also to allow small unwanted species to escape (Broadhurst et al. 2014). Such devices have been effective in reducing accidental catches of seabirds (Morris et al. 2011), seals (Königson et al. 2015), and terrapins (Roosenburg & Green 2000), and therefore may be considered when trying to reduce unwanted catch of subtidal benthic invertebrate species.
Evidence related to the use of other “bycatch reduction devices”/“excluder devices” on pots and traps are summarised under “Threat: Biological resource use – Fit one or more mesh escape panels/windows 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.
Königson S., Lövgren J., Hjelm J., Ovegård M., Ljunghager F. & Lunneryd S. G. (2015) Seal exclusion devices in cod pots prevent seal bycatch and affect their catchability of cod. Fisheries Research, 167, 114–122.
Morris A.S., Wilson S.M., Dever E.F. & Chambers R.M. (2011) A test of bycatch reduction devices on commercial crab pots in a tidal marsh creek in Virginia. Estuaries and Coasts, 34, 386–390.
Roosenburg W.M. & Green J.P. (2000) Impact of a bycatch reduction device on diamondback terrapin and blue crab capture in crab pots. Ecological Applications, 10, 882–889.
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 undersized mud crabs when fitted with escape frame, compared to conventional traps without escape frames. The proportion of undersized crabs caught in traps fitted with frames appeared lower (2%) compared to conventional traps (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 (0.06 crabs/trap) and conventional traps (0.13 crabs/trap). Conventional traps have four 300 × 200 mm funnel entrances but no escape frames. Conventional traps were modified by fitting two 46 × 120 mm escape frames. 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.