A trap with a twist: Evaluating a bycatch reduction device to prevent rockfish capture in crustacean traps

Background/Question/Methods

Improving the catch specificity of commercial fisheries is an ongoing challenge for managers around the world. The use of modifications to reduce bycatch (or the inintentional capture of non-target species which occurs during fishing) has been successful in some industries, but ongoing efforts to reduce the ecological impact of fishing require further development of these Bycatch Reduction Devices (BRDs).  In our study we field-tested novel devices designed to exclude rockfish (Sebastes spp.), several species of which are threatened by fishing on the Pacific coast of North America, from traps used to catch spot prawns (Pandalus platyceros).  The devices tested included simple reductions in the size of the trap openings as well as bent-tunnel openings, which consisted of a series of stainless steel rings attached to the inside of the trap which were meant to prevent the entry of fishes while allowing for the capture of prawns.  We deployed commercial traps equipped with each BRD in order to determine whether these modifications could be suitable candidates for use in the commercial spot prawn fishery.

Results/Conclusions

We found that a simple reduction of trap opening size was ineffective at reducing rockfish bycatch, or the catch of other non-target fish species.  By contrast, traps equipped with bent-tunnel BRD's caught no rockfish, and caught fewer fish overall than unmodified control traps.  Bent-tunnel BRD's were particularly effective at excluding larger fish body sizes, which correspond with the sizes of fishes commonly caught as bycatch in commercial prawn traps.  However, prawn catch rates were reduced significantly across all gear modifications, and with most BRDs, large prawns were excluded more than small prawns.  Through analysis of videos collected in situ, we found that prawn attempts to enter traps took longer and were more likely to fail with BRD-equipped than with unmodified commercial traps.  Prawns often became stuck between the rings of the bent-tunnel BRDs, which suggests avenues for design refinements.  We conclude that the bent-tunnel opening has the potential to be a useful device for excluding rockfish in the fishery, but improvements will be necessary to increase prawn catch.