SPC Researches Impact Of 1000 FADs In PNG Tuna Fishing Groundsff

Tuna landings from western and central Pacific region were estimated to exceed 2.14 million metric tons in 2005, representing a new record for the fishery that has seen the total catch of skipjack, yellowfin and bigeye tuna close to 2 million mt/year since 2001. Effort by some sectors of the fishery has decreased steadily, such as those utilizing live-bait for pole and line operations, while total landings have increased due primarily to increases in large-scale purse seine effort across the region. Purse seine vessels have become increasingly efficient through a combination of technological advances and accumulated experience. A significant factor to increasing efficiency by purse seine fleets has been linked to their use of fish aggregation devices (FADs. The Oceanic Fisheries Programme of the Secretariat of the Pacific Community (SPC) is conducting a medium-scale tagging and assessment project in collaboration with the National Fisheries Authority (NFA) of Papua New Guinea (PNG). The objectives of this project are to obtain information on:

- the medium and large-scale movements of tuna within and from the PNG zone;

- the current exploitation rates of tuna within the PNG EEZ by all fisheries;

- the trophic status of tuna from free-swimming tuna schools and tuna found in association with FADs, natural floating objects and seamounts;

- the variability and extent of bycatch from PNG purse seine fleets;

- the dynamics of tunas associated with anchored FADs.

These objectives are being addressed through a short-term, but intensive tagging effort that will produce data useful for regional stock assessments of the principal target species. The project is being funded by several domestic and international sources including the PNG National Fisheries Authority, the New Zealand Agency for International Development, the Australian Centre for International Agricultural Research, the European Commission, the Global Environment Facility and the University of Hawaii Pelagic Fisheries Research Program.

The study site is particularly suited to an examination of medium-scale movement and FAD-related issues, as it is based within the archipelagic waters of PNG that encompass the highly productive Bismarck and Solomon Seas. These waters have been developed for large-scale tuna harvesting by PNG domestic and domestically-based foreign purse seine fleets, primarily through the use of anchored FADs.

Estimates of FAD numbers vary widely but close to 1000 anchored FADs are believed to be in use and a total of 1000 anchored FADs are permitted under conditions of the NFA National FAD Management Policy (Figure 1). Tuna landings from the study site have increased rapidly and have remained above 100,000 mt per year since 2003.

Tuna landings by PNG domestic and licensed foreign purse seiners in the outer PNG zone have been close to 200,000 mt during the same period. Obviously, the impact of the FADs and FAD fishery, both domestically on bordering areas is a critical concern to the region and the Western and Central Pacific Fishery Commission.

Figure 1.  Ancored FAD positions in the Bismark and Solomon Seas bordering Papua New Guinea.

The project objectives are being addressed by six months of vessel charter divided into two 3-month tagging cruises in 2006-07.  The SPC has chartered the pole-and-line vessel Soltai 6, owned and operated by Soltai Fishing and Processing Ltd, a Solomon Islands based company (Figure 2). Unlike previous large-scale SPC tagging programs, the PNG Project is using a combination of conventional, sonic, internal archival and popup satellite transmitting tags to address different aspects of tuna movement and behavior. Tissue and stomach samples are also being taken from retained catch to support trophic studies on tuna condition in relation to FADs and seamounts and for comparisons with other regions.

Figure 2. The Soltai 6 , chartered to conduct tagging and research activities,

seen circling an anchored FAD in PNG waters.

 Cruise 1 which concluded in November 2006 was highly successful, resulting in 22,430 conventional, 73 archival and 47 sonic tag releases of all three tuna tropical tuna species: skipjack, yellowfin and bigeye tuna. The majority of tag releases were made on schools found in association with anchored FADs with the remainder split between schools found near drifting logs, seamounts, current lines or were unassociated (free-swimming) schools. The species composition of conventional tag releases (62:35:3) came very close to project target of 60% skipjack, 30% yellowfin, 10% bigeye, but fell short on bigeye numbers that proved difficult to capture in quantity with pole-and-line gear. However, the overall tag release numbers were almost 50% above the target level of 15,000 set for the first cruise due to an efficient vessel and an excellent working relationship between the SPC staff, the PNG national counterparts onboard and the hard working Solomon Island crew. Already, the recovery rate of tags is approximately 15%, with recovered tags continuing to be received on almost a daily basis. Most of the tags have been recovered by purse seiners fishing in the Bismarck Sea and surrounding areas, with the tags being found by fishing crew and unloaders in PNG ports. However, a number of tags have been found in Philippines and Thailand from transshipments of PNG-caught tuna, and in Japan from Japanese purse seiners fishing in the PNG area.

Information on the vertical behavior of yellowfin and bigeye tuna is of great interest to the WCPFC, particularly in relation to FAD aggregations. This information is necessary to refine habitat-based fishery models and to evaluate options to improve targeting of desirable species while reducing the take of juvenile or undersize tuna by purse seine gear. These subjects are being investigated both archival tagging and by using anchored FADs as acoustic listening stations to monitor the movement and behavior patterns of tuna implanted with sonic transmitter tags. This technique was pioneered in Hawaii and was successfully adapted during Cruise 1 in PNG by attaching sonic receivers to the FAD floats, thus allowing easy deployment, retrieval and downloading of sonic data (Figure 3). The medium size bigeye and yellowfin suitable for sonic and archival tagging were caught primarily during night handline operations close the FADs.

Figure 3.  An acoustic receiver (arrow) suspended below and anchored FAD float.

Cruise 2 will begin in February 2007, initially concentrating in the Solomon Sea and eastern Bismarck Archipelago. SPC and contracted personnel will concentrate on increasing the numbers of bigeye tag releases and developing workable procedures to tag and release all three tuna species with conventional and electronic tags during normal pole-and-line operations.

Historically, the SPC has conducted large-scale tuna tagging programs as a means to assess stock size and exploitation rates in the WCPO region at roughly decadal intervals. These past projects that defined movement and exploitation rates prior to recent developments in regional fisheries, particularly large-scale FAD deployment, lend a great deal of analytical power to data resulting from the PNG effort. It is hoped that additional funding support will be found to allow a follow-on Phase 2 project in areas beyond PNG. This concept was strongly supported at the recent Western and Central pacific Fisheries Commission meeting in Apia, Samoa.

For further information or to report a recaptured tag, visit the SPC Oceanic Fisheries Programme tagging website at: http://www.spc.int/OceanFish/Html/TAG/index.htm