Testing Modified Deep-Set Buoy Gear to Minimize Bycatch and Increase Swordfish Selectivity
This project investigates the use of alternative deep-set buoy gear (DSBG) configurations for the targeting of swordfish (Xiphias gladius) at depth during the day off the coast of southern California. Gear configurations presented in this work build upon previous DSBG studies that incorporate regional depth distribution data from both swordfish and non-target species into the gear design. Multiple test configurations were developed and trialed from July through January of the southern California 2013-2014 swordfish season. Hook depths were continuously monitored using depth and temperature data loggers deployed on each set of test gear. All deployments used 8m gangions of 1.8mm monofilament and 18/0 circle hooks baited with either mackerel (scomber spp.) or squid (illex spp.). Mainline characteristics included 250-350m of 2.8mm monofilament and a 4kg drop sinker. A total of 12 experimental deployment days (1,850 hook-hours) were performed to evaluate hook depth distribution, deployment feasibility and the effects of additional hooks set-1 of gear. An additional 12 deployment days (2,590 hook-hours) were performed using the two test configurations that resulted in consistent depth distribution between 250-350m and maintained strike detectability for rapid release of nontarget species. Final test trials resulted in the capture of swordfish (11), blue sharks (Prionace glauca) (6), mako shark (Isurus oxyrhinchus) (1) and salmon shark (Lamna ditropis) (1). The refined DSBG configurations tested in this study continue to suggest high selectivity for swordfish. The test configurations developed in this study will be used by cooperative fishers during the 2014-2015 fishing season. This work constitutes one component of the necessary steps for fishery implementation off the coast of southern California.