Escape gaps in recreational panulirid traps: Reducing catches of undersized Sagmariasus verreauxi while increasing fishing power for legal sizes

In response to a lack of data supporting (or otherwise) legally mandated escape gaps in an Australian recreational trap fishery for eastern rock lobster, Sagmariasus verreauxi, the effects of all prescribed options on catches were investigated. Round traps without escape gaps (control) were compared against those with either one (57 × 500 mm), two (both 57 × 250 mm) or three (all 57 × 200 mm) rectangular openings (i.e. all similar areas) evenly located around the base of the trap perimeter. All traps with escape gaps retained significantly fewer undersized (by 54-84%) but more legal-sized (by 1.6-2.8 times) S. verreauxi than the control. Irrespective of escape gaps, there was also a positive association between antennae loss by S. verreauxi and trap soak time, although only one undersized individual died (for a total associated discard mortality <2%). These observations are explained by possible density-dependant behavioural responses of trapped S. verreauxi, with legal-sized individuals replacing escaping juveniles and increased physical interactions among all catches the longer they remained in traps. Escape gaps could be promoted in the fishery, not only for their utility in reducing catches of undersized individuals, but via the potential for almost triple the fishing power for targeted catches.