Utility of multiple escape gaps in Australian Scylla serrata traps

As part of attempts to promote more selective recreational and commercial portunid trap fisheries in south-eastern Australia, the effects of single and multiple rectangular escape gaps (46 × 120 mm) on catches of the targeted giant mud crab, Scylla serrata and incidental species were investigated. Twenty-five collapsible netted round traps comprising five replicates of those with zero (controls), one, two, three or four escape gaps positioned at the base were simultaneously fished in two estuaries by three commercial fishers. Compared to the control, and irrespective of estuary, all traps with escape gaps similarly maintained catches of legal-sized S. serrata (≥85 mm carapace length-CL) while reducing undersize numbers by 85-93%. At one location, 21% of the portunid catch included the smaller blue swimmer crab, Portunus armatus (legal size of ≥60 mm CL); the numbers of which were also significantly lower by 73-96% (across all sizes) in escape-gap traps than the control and with greater escape from traps with multiple escape gaps. Catches of two abundant teleosts were not affected by either single or multiple escape gaps. The results were attributed to species-specific responses to catch densities and while the data reiterate the utility of escape gaps for improving trap selectivity, configurations might need to be fishery specific and/or spatially regulated according to distributions of the key target and incidental species.