Alternative branch line weight designs to improve crew safety and reduce bycatch of sensitive species groups in pelagic longline fisheries
Placing weights near hooks in pelagic longline fisheries can reduce seabird, sea turtle, shark and billfish bycatch. However, vessels that do not use a wire leader on branch lines, such as in the Hawaii-based longline swordfish fishery, do not place weights close to the hook, or use any weights on their branchlines, in part, due to safety concerns: If branchlines break during hauling, which frequently occurs when sharks are caught and bite off the terminal tackle, the weight can fly back at the vessel at extremely high velocity, infrequently causing serious injury, and in very rare cases, killing crew. A dockside trial and research fishing trip on a Hawaii longline swordfish vessel was conducted to assess the efficacy and commercial viability of two experimental designs of safer weights. Results from the dockside trial indicate that the two experimental weights present a substantially reduced risk of injury to crew relative to conventionally employed line weights. Results from one experimental fishing trip demonstrated that an experimental weight performed as designed, however, the sample size was too small to demonstrate a significant difference in weight behavior after lines broke during gear retrieval between the control and experimental weight. Additional research and development is needed to overcome identified practicality issues (threading one of the experimental weights onto the line, gear tangling due to absence of a swivel), and durability of the experimental weights, while keeping the per-unit cost low enough to be economical and competitive with conventional lead center swivels. All problems encountered with the two experimental leads are likely possible to overcome. With additional research and development, it will be possible to develop a simple, inexpensive, and durable safer lead weight for use in pelagic longline gear.