The initial Skipjack Survey and Assessment Programme (SSAP) was carried out from 1977-1981, with main aim of investigating skipjack dynamics throughout the very wide SPC area (see Figure 1). At this time the surface catch, mostly taken by pole-and-line vessels, was around the 500,000t level, with a longline fishery taking 200,000t of mostly yellowfin tuna.
It was the first large scale tagging project undertaken in the Western and Central Pacific Ocean.
More specifically, the project aimed to provide
- a better understanding of the migrations and stock structure of skipjack, thus determining the degree to which fisheries in different areas exploit the same stock and hence interact with each other
- valuable survey information on the general distribution and availability of skipjack and baitfish as the basis for further development and management of these resources within the region
- better knowledge of population parameters (growth, mortality etc) of each skipjack stock, this enabling better assessment of each stock and the effect of fishing on them
The proposal aimed to tag and release 100,000 skipjack tuna over three years throughout the region to meet these objectives.
Figure 1. Geographical distribution of total catches of albacore, bigeye, skipjack and yellowfin tuna, 1999-2003. The red line indicates the eastern boundary of the Western and Central Pacific Fisheries Convention Area.
The operational phase commenced in October 1978 using the chartered vessel Hatsutori Maru.
Tagging activities were designed so that they complemented previous national scale tagging activities in the region with tagging undertaken in Papua New Guinea, Solomon islands, Vanuatu, New Caledonia, Fiji, Tonga, Wallis and Futuna, American and Western Samoa, Tuvalu, Kiribati, Tokelau, French Polynesia, Cook Islands, Australia, New Zealand, Pitcairn Island, Norfolk Island, Nauru, Guam, Federated States of Micronesia, Northern Mariana Islands, Palau and Marshall Islands.
The tagging in each country extended over approximately one month.
The SSAP was funded through contributions by Australia (33%), Japan (19%), France (19%), New Zealand (13%), USA (12%) and United Kingdom (7%).
Using two different chartered pole-and-line vessels supplied by Japan and with operational costs funded by various donors (total US$ 3.8 million), 150,000 tunas (95% skipjack tuna) were ultimately tagged and released over a wide area east of 140E for a recapture rate of around 4%. Baitfish surveys and other biological research activities were also carried out.
Subsequent analyses of the tag-recapture data demonstrated for the first time the very large biomass of skipjack available in the region, and highlighted the potential for considerable increases in the tuna catch, especially of skipjack, at the prevailing low exploitation rates, then estimated at around 4% (Kleiber et al. 1987). These results were in large measure responsible for generating the increased interest in the WCPO by international fleets.
The SSAP work was regarded at the time as ground-breaking, generating various other information on skipjack for the first time, including movement, mortality and spatial interaction data, and demonstrating the value of large-scale tagging for assessments of highly mobile species. Indeed, much of the information is still used as an important reference point at that level of exploitation. Little information was however gathered on other tuna species of importance to the fishery, viz. yellowfin, bigeye and albacore.
Through the 1980s, the purse seine fishery expanded rapidly in the equatorial waters of the WCPO, with the total purse seine catch ultimately exceeding one million tonnes in 1991 (Figure 2). The longline fishery, on the other hand, declined to some extent until the early-1990s, with a shift to targeting more valuable bigeye tuna.
Figure 2. Catch by species in the WCPO, 1980-2002.