Behavior of target and non - target species on drifting FADs and when encircled by purse seine gear WCPFC -

Empirical and observational data were collected from 31 sets made from a tuna purse seine vessel during the International Seafood Sustainability Foundation’s (ISSF) WCPO bycatch reduction research cruise. Simultaneously, skipjack (Katsuwonis pelamis), yellowfin (Thunnus albacares), and bigeye (T. obesus) tuna and silky sharks (Carcharhinus falciformis) were implanted with pressure sensing acoustic transmitters and monitored on drifting FADs in the same areas. Untested assumptions relating to natural behavior of encircled fish in purse seine gear were clarified; divers observed separation of target species by species as well as size. Additionally, nontarget species consistently separated themselves from target species and remained shallow. This species segregation was consistently observed during all sets and lasted throughout the duration of the haul until the beginning of sacking was reached, at which point individuals and schools were forced to intermingle. Acoustic tagging data confirms these behavioral characteristics displayed naturally while associated with a floating object, which is well documented by other tagging studies on FADs. These observations provide much needed insight to behavioral patterns of non-target and unwanted species, which may inform further research and development of options to selectively release or sort these from the net before these animals sustain mortal injuries. Background/Relevance The International Seafood Sustainability Foundation’s (ISSF) bycatch reduction project is an ongoing process to investigate and test methods for reducing non-target and unwanted catch in the tuna purse seine fishery, with a specific focus on reducing the take of these animals around fish aggregating devices (FADs). The Western Central Pacific Ocean (WCPO) research cruise was conducted during May-July 2012 aboard the F/V Cape Finisterre, based in Pago Pago, American Samoa. The research objectives of this cruise were to improved data collection and selectivity of the region’s drifting FAD (raft) fishery. Research permits were obtained for the Tokelau, Tuvalu, Solomon Islands, Kiribati, and Cook Islands Exclusive Economic Zones (EEZs) to accommodate a large research area, but fishing only occurred in the Tokelau, Tuvalu and Kiribati EEZs as well as the high seas pocket in this region. The objectives of the study addressed in this module include: 1. To observe the behavior of tuna and bycatch species in the purse seine net to explore possibility of isolating and releasing in good condition bigeye tuna, sharks and other non-target species. 2. Determine if economically viable landings of skipjack and yellowfin tuna can be maintained while avoiding bigeye, small tuna and miscellaneous bycatch species. 3. To determine if bigeye, yellowfin and skipjack tuna separate horizontally after dawn allowing the targeting of pure skipjack or skipjack and yellowfin mixed schools both at the FAD and away from the FAD that they were associated with during the previous evening. Methods The objectives were addressed using 2 methods: 1) SCUBA divers deployed inside of the net after approximately 75% of net rolling was completed, made observations during visual surveys and collected photographic and video data on behavior of target and non-target catch; and 2) acoustic tagging of bigeye, yellowfin, skipjack, and silky sharks on drifting FADs in the study area. Dive Surveys Divers were deployed inside of the net during 15 of the 31 total sets for the cruise. Free divers were sent in on all but a few sets. After an initial assessment of the conditions inside of the net from the surface, the dive was commenced and divers descended to depths between 80’ and 120’. The divers then slowly ascended, visually surveying as much of the area inside of the pursed net as possible without disturbing the aggregation of fish. Total dive time inside of the net was approximately 18-25 minutes. The end of the dive usually coincided with the final few minutes of net rolling, in which the corks become enclosed enough that divers must exit the net to ensure safety. Once outside the corkline, the divers observed the beginning of the sacking up process, and then exited the water. Canon G-12 cameras with underwater housings were used to obtain digital still images, and GoPro Hero HD2 video cameras were utilized for video. Acoustic Tagging Tagging was conducted on three occasions at floating objects in the study area on drifting FADs equipped with Zuniball GPS-Sonar capable buoys. Fish were captured using sport rod and reel fishing gear, with barbless hooks to minimize hook damage. Each fish was netted and brought aboard with a knotless webbing nylon mesh net, and hydrated for the duration of the tagging procedure with salt water via a hose through the mouth. Vemco V9P and V13P pressure sensing acoustic coded pinger tags were surgically implanted into the peritoneal cavity each fish, and the incision was closed with 2 sutures. An 11cm Hallprint conventional dart tag was placed by the second dorsal fin to aid in locating recaptured fish. Each fish was immediately released in excellent condition. Vemco VR2W acoustic receivers were fastened to each FAD which tagged fish were released and then retrieved when the FAD was set on. Results During the 40 day research cruise, a total of 31 sets were made. Thirty of these sets were on floating objects, and one on a free school. Of the 30 floating object sets, 27 occurred around right before dawn, the typical time for a floating object set in the WCPO fishery. Set size ranged between 7-174 mt, averaging 42.67 mt. 1. Observations made by divers while inside the net Several consistent behavioral observations emerged from this experiment: a. Grouping of similar size fish by species Skipjack, yellowfin and bigeye tuna observed during these surveys appeared to remain separated by size class, and also by species. For example, small (35-40cm) to medium (40-55cm) sized skipjack displayed cohesive schooling behavior with each other, and avoided separate schools of larger skipjack or yellowfin and bigeye. Large (>100cm) yellowfin also schooled together and rarely split up. These large yellowfin occasionally had large (>90cm) bigeye on the periphery of the school as well. Some mixing of similar sized small (<60cm) yellowfin and bigeye did occur, which formed mixed aggregations with each other. However, on multiple occasions these small yellowfin and bigeye were observed to separate themselves from each other and form loose schools of mono specific groups. b. Vertical stratification of fish by size and species Similar sized fish schools also displayed vertical stratification during most of the dive surveys. Large yellowfin and bigeye occupied the lowest portions of the pursed net, bigeye were found between 30-60m. Size separated schools of skipjack, as described in (a) occupied the middle of the water column, bigeye between 15-30m, and small yellowfin and bigeye occupied the upper portion of the water column from 10-20m. Some mixing occurred but this vertical stratification of species seemed to remain constant until it was physically impossible towards the end of the net rolling when space became confined. c. Non-target species separation from target tuna species Non target species including mahi mahi (Coryphaenus hippurus), wahoo (Acanthocybium solanderi), rainbow runner(Elagatis bipinnulata), and silky sharks were observed spending the majority of their time in the upper 20m of the water column, usually in mono specific schools, containing varying sizes of fish. Silky sharks seemed to consistently end up at the far side of the net away from the fishing vessel, inspiring the design, construction, and testing of a release panel in the net to attempt to release them and other non-target species as described in EB-WP-14.