The impacts of commercial fishing extend far beyond direct effects on targeted species. As much as 40% of global marine catch is attributable to bycatch, or the capture of non-target organisms which occurs during fishing. The amount of bycatch in a fishery is determined in part by the selectivity of the industry's fishing gear, and bycatch mitigation often focuses on improving the selectivity of these gears. This thesis explores bycatch mitigation through the design and evaluation of bycatch reduction devices (BRDs), or fishing gear modifications aimed specifically at reducing non-target catch while maintaining the catch of target species. I examine BRDs using a three-pronged assessment, which tests a modified gear's effects on non-target catch, on target catch, and on practicality for use in commercial fisheries (all relative to unmodified gear). I first perform a global-scale meta-analysis on technologies designed to protect elasmobranchs (sharks and rays) from longline fisheries. I show that most technologies are broadly ineffective at reducing elasmobranch bycatch, and that many studies fail to adequately assess novel BRDs across all three dimensions of gear performance. The remainder of my thesis focuses on the research and development of BRDs for a British Columbia fishery which employs trapping gear to capture spot prawns (Pandalus platyceros). Using data from fishery-independent surveys, I show that these traps catch rockfish (Sebastes spp.) as bycatch, a multi-species genus which is depleted due to overfishing and which suffers high discard mortality due to barotrauma incurred during the fishing process. I demonstrate that a novel underwater camera system can be used to study prawn traps in situ, and use insights from this analysis to inform the design of BRDs for prawn traps. I conclude my thesis with an assessment of BRDs of my own design, using both catch data and in situ observations conducted using my underwater camera apparatus. Overall, this thesis demonstrates the challenges in designing effective BRDs, and provides a framework for assessment that can be used as a template in future studies of fishing gear design.

Seabird Bycatch significantly adds to the knowledge base of seabird mortality in commercial fisheries, and emphasizes the importance of comprehensive solutions. The product of a 1999 symposium held by the Pacific Seabird Group, Seabird Bycatch is a response to escalating bycatch, a global conservation and fisheries management issue.

To sustainably and responsibly harvest commercial aquatic species in the world's fisheries, consideration must be given towards the negative physical and biological effects that fishing gears place on marine ecosystems. Fish habitat degradation, bycatch of undersized and non-target species, carbon footprint, reductions in biodiversity and biomass are just some of the negative impacts of fishing gears. One novel method to reduce impacts while maintaining commercially viable catch rates of target species is through modification of fishing gears. Two experimental studies, conducted for this thesis, evaluated the catch characteristics of innovative, modified fishing gears designed to mitigate ecological concerns specific to each study's respective fishery. In the first study, the Newfoundland cod pot was modified in an attempt to target flatfish species while avoiding the capture of snow crab (Chionoecetes opilio). Major findings include the importance of artificial light and entrance shape in capturing American plaice (Hippoglossoides platessoides). Also, non-baited pots that contained only artificial light were successful in capturing plaice while greatly reducing the capture of snow crab. In the second study, at-sea catch characteristics of northern shrimp (Pandalus borealis) and non-targeted bycatch species were compared between two trawls, one containing a traditional rockhopper ground gear currently used in the northern shrimp fishery, the other containing an experimental ground gear designed to reduce seabed contact. Catch rates and size of shrimp were found to be comparable between trawls however the experimental trawl captured significantly more bycatch.

Bycatch is the unwanted or non-target part of the catch taken by fishermen. It is either discarded at sea or used for human or animal consumption. The capture of bycatch may pose a threat to species diversity and ecosystem health because this part of the catch is usually unregulated. In tropical shrimp-trawl fisheries, bycatch often consists of juvenile food-fish species and is therefore a threat to food security and sustainable fisheries production. Bycatch is a global problem that must be addressed. This Guide to Bycatch Reduction in Tropical Shrimp-Trawl Fisheries is designed for fishermen, net makers, fishing technologists and others interested in a practical guide to the design, use and operation of effective bycatch reduction devices. Fishery managers, policy-makers and legislators will find this guide useful to help develop specifications governing the design and application of these devices in a shrimptrawl fishery. The issue of bycatch is not going away and scrutiny of fishing activity is increasing. All fishermen are strongly urged to use appropriate bycatch reduction measures to help maintain the productivity of the fishery and the long term prosperity of the fishing industry. By responding appropriately, fishermen can help to protect the marine environment and assist global food security both now and in the future. Also published in French and Spanish.

'The Sunken Billions: The Economic Justification for Fisheries Reform' shows the difference between the potential and actual net economic benefits from marine fisheries is about $50 billion per year, or some $2 trillion over the last three decades. If fish stocks were rebuilt, the current marine catch could be achieved with approximately half the current global fishing effort. This illustrates the massive overcapacity of the global fleet. The excess competition for the limited fish resources results in declining productivity, economic inefficiency, and depressed fisher incomes. The focus on the deteriorating biological health of world fisheries has tended to obscure their equally critical economic health. Achieving sustainable fisheries presents challenges not only of biology and ecology, but also of managing political and economic processes and replacing pernicious incentives with those that foster improved governance and responsible stewardship. Improved governance of marine fisheries could regain a substantial part of this annual economic loss and contribute to economic growth. Fisheries governance reform is a long-term process requiring political will and consensus vision, built through broad stakeholder dialogue. Reforms will require investment in good governance, including strengthening marine tenure systems and reducing illegal fishing and harmful subsidies. Realizing the potential economic benefits of fisheries means reducing fishing effort and capacity. To offset the associated social adjustment costs, successful reforms should provide for social safety nets and alternative economic opportunities for affected communities.

"The Airborne Streak Tube Imaging LIDAR (ASTIL) was evaluated for use in detecting schools of tuna in the Eastern Tropical Pacific (ETP) waters in order to aid in reducing bycatch of dolphin associated with yellowfin tuna. Three airborne experiments were conducted and data were collected for southern bluefin tuna, yellowfin tuna, akule (trachiurops crumenophthalmus), giant bluefin tuna (GBFT) and dolphin. The LIDAR signature of tuna was studied and extended to an evaluation of fish and fish school detection of GBFT using STIL experimental data. The utility of fish school detection was confirmed for GBFT in terms of detection statistics for binary hypothesis testing and also by direct implementation of a three-dimensional matched filter algorithm. Based on the GBFT observations, modeled performance estimates were made for yellowfin in the ETP for an upgraded ASTIL system."--p.11

Bycatch Reduction Devices (BRDs) are specific devices that can be incorporated in a fishing gear in order to exclude or reduce non targeted and unwanted catch in a fishing system and thereby making it more selective. The main objective of the study was to design, development and comparative evaluation of hard bycatch reduction devices (BRDs made out of metallic rods) appropriate for small scale mechanised sector and also to conduct a characterisation study of trawl catch and existing trawling systems operated off Cochin in India. In a review 8 different classes of hard BRDs used world wide were identified and the prevailing trends of trawlers and trawl nets were assessed by the characterisation studies. In bycatch analysis about 282 marine species were encountered in the trawl nets and the average bycatch in Cochin waters was about 87%. Experiments were conducted using variations of hard BRDs showed promising performance in terms of bycatch exclusion and lowest target catch loss.