In last August 2014, SPC fisheries scientist Bruno Leroy was in charge for this 25 day cruise that drove the Tongan FV Pacific Sunrise through the waters of American Samoa, Tokelau, Cook Islands and Kiribati-Phoenix Islands. The Central Pacific (CP) tuna tagging cruises were originally designed to tag tuna in areas where pole and line boats could not really work due to the scarcity of live baits and also to increase the releases of tagged bigeye tuna that are rarely caught in the surface fisheries in the western part of the Pacific.

The success of the project has been demonstrated after the completion of 9 CP cruises that allowed the release of more than 35,500 bigeye tuna since 2008. Over 10,000 recoveries brought priceless information to better assess the stocks of this species across the whole Pacific equatorial region.

These previous CP cruises caught, tagged and released fish associated with some of the Tropical Atmosphere Ocean (TAO) mooring that measure surface meteorological and subsurface oceanic parameters. During the organisation of CP10, opportunity arose to collaborate on a research project funded by International Seafood Sustainability Foundation (ISSF). The idea was to deploy sonic tags in the main species of fish that aggregate under drifting FADs (dFADs) to study their behaviour. Sonic (acoustic) tags were equipped with depth sensors and transmit signals that could be recorded when there are in the detection range of a receiver. When this one is attached to a FAD, the presence/absence of the tagged fish can be studied along with their vertical distribution under the FAD.

The company Tri Marine, a major player in the tuna industry and one of the founders of ISSF, agreed to provide us access to real time positions of their dFADs in the vicinity of the cruise. Tri Marine operates a fleet of purse seine vessels with 10 of those being based in Pago Pago. The given dFADS were equipped with IRIS satellite buoys that are monitored through a communication system provided to the cruise by the French company Thalos. This system includes an external Iridium satellite antenna linked to a laptop via a cable and a connection box. Without such tracking system it is almost impossible to retrieve a dFAD in the open ocean.

3 dFADs were equipped with a satellite communicating acoustic receiver manufactured by Vemco company. These types of units utilize Iridium satellite communication and eliminate the need to retrieve the receiver to get the information. 68 fish were implanted with sonic tag between the 3 equiped dFADs. Half of the fish were tuna from the 3 species (bigeye, skipjack, yellowfin) and the other half was composed of sharks, triggerfish, rainbow runner and wahoo.

CP10 has been an unusual cruise amongst the other Central Pacific tagging experiments. The cruise was hampered with the lack of large bigeye aggregation under the TAOs along the 170 meridian and with the presence of natural baits in the area making the fish not biting our fishing gears. On the other hand, the first attempt to release tagged fish around drifting fads has been successful. The collaboration between SPC, Trimarine and ISSF proved to be working well. This new experience will, no doubt, be followed by more research cruises in a next future

Check out the cruise report

Have a look to the CP10 short movie