Modifications to reduce bycatch in prawn trawls: A review and framework for development

The incidental capture of non-target species from prawn trawling has recently attracted worldwide attention. Primarily, concerns arise from the perception that prawn trawls catch and discard large numbers of juveniles of species that, when larger, are targeted in other commercial and recreational fisheries. While several management options are available, the majority of fisheries in the world have attempted to address this issue through physical modifications to trawls, designed to improve selectivity. The types of modifications used reflect fishery-specific characteristics; however, most can be broadly classified into two categories, including: (1) those that separate species by differences in behaviour; and (2) those that mechanically exclude unwanted organisms according to their size. In the present paper, I provide a chronological review of publications in the primary literature that describe experiments examining modifications within these categories. This review shows that inherent variabilities among different fisheries greatly influence the types of designs that need to be applied and although some designs have the potential for application across different fisheries, significant modification and re-evaluation are often required. By collating information from previous studies, I also propose a framework encompassing the various stages involved in developing and applying successful modifications in prawn-trawl fisheries. The key stages identified include: (1) quantification of bycatches and accumulation of fishery-related information; (2) examination and re-evaluation of modifications; (3) assessment of damage inflicted on escaping individuals; and (4) promotion of recommended designs.