This thesis provides an overview of recent selectivity studies conducted in eastern North Pacific trawl fisheries (e.g., West Coast groundfish bottom trawl fishery, Pacific hake [Merluccius productus] fishery, and ocean shrimp [Pandalus jordani] fishery). Collectively, these fisheries play a significant role in supporting fishing jobs, income, and coastal communities. However, bycatch can impact fishers ability to fully utilize the fisheries resource. Thus, developing gear modifications to reduce bycatch are increasingly important. In this thesis, results from VIII selectivity research papers addressing bycatch issues in eastern North Pacific trawl fisheries are presented.
In the U.S. West Coast groundfish bottom trawl fishery, constraining species such as darkblotched rockfish (Sebastes crameri), sablefish (Anoplopoma fimbria), and Pacific halibut (Hippoglossus stenolepis) bycatch can impact fishers ability to maximize their quota shares of healthier groundfish stocks. In Papers I-III, results from sea trials evaluating sorting grid bycatch reduction devices (BRDs) to reduce catches of these species are presented. Results from these papers demonstrate the ability of sorting grid devices to reduce bycatch while retaining a relatively high proportion of the targeted species. In Paper IV, the efficacy of T90 mesh codends to improve catch composition in the Dover sole-thornyhead-sablefish complex fishery were examined. In this fishery, where catches of juvenile and sub-adult sablefish are affecting fishers ability to achieve a higher ex-vessel value (e.g., landed value) of the sablefish resource, and higher attainment rates of Dover sole (Microstomus pacificus), results presented in Paper IV demonstrates that T90 mesh codends have potential to increase fishers opportunities to capitalize on their Dover sole individual fishing quota and enhance their net economic benefits while more effectively attaining their quota shares of sablefish.
In Papers V-VIII, results are presented from studies testing the efficacy of artificial illumination (e.g., light-emitting diodes [LEDs]) to reduce fish bycatch. In Paper V, research tested if simple enhancements to the visibility of a low-rise selective flatfish trawl headrope could improve bycatch reduction for darkblotched rockfish, sablefish and Pacific halibut. Findings from Paper V suggest that use of illumination could have potential applications for reducing bycatch under particular situations. For example, fishers seeking to reduce sablefish catches and/or Pacific halibut bycatch when targeting English sole (Parophrys vetulus) and petrale sole (Eopsetta jordani) could potentially benefit from illuminating the trawl headrope, whereas fishers seeking to target Dover sole and/or sablefish but avoid darkblotched rockfish, would likely not benefit from using illumination. In Papers VI-VII, studies evaluating the efficacy of LEDs to reduce eulachon (Thaleichthys pacificus) and groundfish bycatch were examined. For eulachon, an anadromous smelt species endemic to the eastern North Pacific, their bycatch is an issue facing the ocean shrimp fishery as the species’ southern Distinct Population Segment was listed as “threatened” under the U.S. Endangered Species Act (ESA) in 2010. Results presented in Papers VI and VII continue to support the hypothesis that there is a significant reduction in eulachon bycatch when artificial illumination is present. For rockfishes and flatfishes, findings suggest their ability to escape trawl entrainment in response to illumination along the fishing line is not as strong as previously indicated. As conservation of ESA-listed eulachon is an ongoing management priority, Papers VI and VII contribute new data on the efficacy of footrope illumination to reduce their bycatch. Lastly, Paper VIII conducted two separate experiments evaluating the influence of artificial illumination on Chinook salmon (Oncorhynchus tshawytscha, a species with ESA listings) behavior and escapement out of a BRD in a Pacific hake midwater trawl. Findings from Paper VIII demonstrate that artificial illumination can influence where Chinook salmon exit out the BRD tested, but also that illumination can be used to enhance their escapement overall. Because ocean distributions of Chinook salmon and Pacific hake often overlap, interactions between Pacific hake trawl gear and Chinook salmon are likely to continue to be an issue facing the fishery. Findings from Paper VIII provides data on a gear modification that can minimize Chinook salmon bycatch.
Lastly, the collective work presented within this thesis has contributed substantially to the development and advancements of gear modifications for reducing bycatch in eastern North Pacific trawl fisheries and the conservation of ESA-listed species.
Papers I, II, and VIII are published in Fisheries Research, Papers III, IV, and V are published in Marine and Coastal Fisheries, Paper VI is published in the International Council for the Exploration of the Sea Journal of Marine Science, and Paper VII is published in the Canadian Journal of Fisheries and Aquatic Sciences.