Increasing the Selectivity of the Stone Crab Menippe mercenaria Trap by the Addition of a Cull Ring

Abstract

The fishery for stone crab Menippe mercenaria in Florida is dominated by plastic traps that do not require a cull ring or device that limits retention of prerecruits and bycatch. An experiment was conducted to determine what size of cull ring would reduce the catch of prerecruit stone crabs and bycatch while maintaining legal catch. Catch compositions of crabs from unmodified plastic commercial stone crab traps and traps fitted with a 54.0-, 55.6-, or 57.2-mm cull ring were compared in the stone crab fishery across Florida's west coast. Traps outfitted with cull rings retained bigger crabs, less bycatch, and fewer prerecruit stone crabs and, for most cull ring sizes tested, yielded the same number of legal-size claws. Retention of prerecruit crabs in traps with cull rings varied among regions because of the sexual dimorphism in carapace length (males, 58.2 mm; females, 64.6 mm) observed when an original crusher claw has reached legal size (>70 mm). We recommend that a minimum size cull ring of 55.6-mm (2 3 ∕ 16 in) be used in stone crab traps fished in state and federal waters off Florida.

Improving size selectivity of round pot for Charybdis japonica by configuring escape vents in the Yellow Sea, China

“…With the installation of large escape vents, the CH50 increased considerably, implying that escape vents can effectively improve the size selectivity of round pots. This result is consistent with the published researches on the other commercially important crustacean pot fisheries (e.g., Guillory et al, 2004;Arana, Orellana & De Caso, 2011;Rotherham et al, 2013;Broadhurst, Millar & Hughes, 2017;Broadhurst, Butcher & Millar, 2017;Broadhurst & Millar, 2018a;Gandy et al, 2018). The exploitation indicators indicated that the pots with 70 mm × 20 mm, 70 mm × 25 mm and 70 mm × 30 mm escape vents released nearly 50%, 75% and 95% of the undersized individuals, respectively, and these three types of pots retained approximately 90% of the legal-sized individuals compared with control pots without escape vents.…”

“…The annual marine Charybdis landings have decreased from 62,581 to 24,259 tons (2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019) in China caused by environmental pollution, over-use of poor-selective fishing gears, and excessive fishing efforts, and this has raised immediate concerns of the Chinese government on restoring the coastal eco-system. Configuring a suitable escape vent was regarded as a simple and effective solution to conserve fisheries resources, mitigate ghost fishing mortality and achieve a balanced harvest in pot fisheries (Boutson et al, 2009;Arana, Orellana & De Caso, 2011;Uhlmann & Broadhurst, 2015;Broadhurst & Millar, 2018b;Gandy et al, 2018). The widespread use of pots in the coastal areas of China means that even marginal improvements in selectivity are likely to have considerable cumulative environmental and ecological benefits.…”

Differential Effects of Three Crab Trap Escape Ring Sizes on Retention of Male and Female Blue Crabs

“…Variation in trap retention based on sexual dimorphism has also been observed for stone crab Menippe mercenaria (Gandy et al. 2018), and Rudershausen and Turano (2009) observed a similar discrepancy in the relationship between CW and CL between male and female blue crab specimens. The results from this study expand on those of Rudershausen and Turano (2009) and examine the potential effects of larger escape ring sizes than have been examined previously.…”

“…This observation is relevant in the context of blue crab management given that females were shown to have a greater CW at CL; the result being that they show greater escapement (i.e., less trap retention) at a given CW, with this discrepancy in escapement between males and females increasing with both CW and size of escape ring. Variation in trap retention based on sexual dimorphism has also been observed for stone crab Menippe mercenaria (Gandy et al 2018), and Rudershausen and Turano (2009) observed a similar discrepancy in the relationship between CW and CL between male and female blue crab specimens. The results from this study expand on those of Rudershausen and Turano (2009) and examine the potential effects of larger escape ring sizes than have been examined previously.…”