In situ video monitoring of by-catch interactions within commercial rock lobster (Jasus edwardsii) fishing traps

The incidental capture of non-target and undersized target species during commercial fishing operations has been identified as a major issue and ongoing challenge for fisheries management. In the Northern Zone rock lobster (Jasus edwardsii) fishery (NZRLF) of South Australia, escape gaps have been mandatory in all commercial fishing traps since 2002 to reduce non-target species (by-catch) catch rates and juvenile lobster mortality. This study used in situ video monitoring of by-catch species in traps with and without escape gaps to understand how by-catch species interact within commercial fishing traps. Twenty-two different by-catch species were observed entering commercial rock lobster traps, 20 of which were temperate reef finfish. Overall, on-board by-catch rates were significantly higher in hauled traps without escape gaps and were dominated by reef-dwelling finfish species, particularly Meuschenia hippocrepis and Notolabrus tetricus. However, in situ video monitoring within traps showed no difference in the maximum number of finfish by-catch (MaxN) in traps with or without escape gaps. We suggest that the difference in by-catch rates between hauled traps with and without escape gaps may be driven by species-specific behavioural interactions within traps prior to hauling. Overall, this study shows that the implementation of escape gaps in the NZRLF has considerably reduced fishery by-catch rates. Furthermore, the use of in situ video monitoring has provided a better understanding of by-catch behavioural interactions within traps, not previously identified in on-board sampling research, which may partly explain the mechanisms underpinning escape gap effectiveness.