Tuna tagging on track

Simon Nicol
On April 2, the 100,000th tuna was tagged as part of the Pacific Tuna Tagging Programme being undertaken in the Western and Central Pacific Ocean, which has the most important tuna fisheries in the world.

The project is on track to be the largest tuna tagging experiment ever undertaken, with over 200,000 tuna eventually expected to be tagged, according to project leader, Dr John Hampton, from the Secretariat of the Pacific Community (SPC).

Tuna fisheries provide important income for many Pacific Islands countries and territories (PICTs), and obtaining high-quality scientific information on the sustainability of the fish stocks is critical for ensuring the long-term future of the resource and the economic benefits derived from it.

What is tuna tagging?

The tagging of tuna involves the live capture of the fish, attachment of a small but visible tag to the fish, measurement of the fish’s length, and its release back into the wild. The fish are tagged and released within a few seconds of capture. The tags are later retrieved from caught fish and used to study the population dynamics, behaviour and ecology of tunaŃin their natural environment and in association with fish aggregating devices (FADs).

In addition to the standard tagging operation using plastic tags embedded in the back of the fish, the project has also tagged tuna using two types of internally implanted electronic tag: acoustic transmitting tags and archival storage tags. Each acoustic tag transmits a unique coded signal and data on swimming depth to monitors attached to FADs, thus enabling scientists to identify the presence of individuals and their behaviour at FADs that are monitored.

Archival tags collect and store data on light intensity, temperature of the water, internal body temperature of the tuna and swimming depth. Figure 1 illustrates data collected on the depth at which the tagged tuna were swimming.

Why tag tuna?

The tuna species being targeted by the project are skipjack, yellowfin and bigeye. Recapture of these tagged fish by fishers in the future will provide critical information on fish growth rates, movement patterns (such as local recruitment, advection and dispersion), and the impact of fisheries on the stocks. This information will be used in annual assessments of the status of the fish stocks (i.e. whether they are declining, increasing or stable), which PICTs will be able to use to determine appropriate management actions. The information derived from the tagging project will result in more accurate and precise assessments of stock status, according to Dr Hampton.

A carefully designed tuna tagging project on a large scale is an expensive proposition and SPC is well equipped to do the job. Over several decades it has fielded large-scale tagging programmes, tagging hundreds of thousands of tuna and analysing the returned tags to reveal much of what we now know about the size of the tuna resource and the movements and behaviour of tropical tuna. The new data provided by the project will help ensure the fisheries are managed using the best possible information.

From PNG and Solomons to the wider Pacific

The Pacific Tuna Tagging Programme is being coordinated by SPC’s Oceanic Fisheries Programme in partnership with all countries and territories in the western and central Pacific, the Western and Central Pacific Fisheries Commission and the tuna fishing industry. Phase 1, which concentrated its efforts on waters around Papua New Guinea and Solomon Islands, has now been completed, with more than 100,000 tuna tagged. Help was provided by the PNG National Fisheries Authority, the Solomon Islands Ministry of Fisheries and Marine Resources, and the Soltai Fishing Company; the latter assisted with the provision of a fishing boat to undertake the tagging.

Phase 1 in PNG and Solomon IslandsŃthe very successful ‘first step’Ńwill this year be extended to the wider Western and Central Pacific region as Phase 2 of the Pacific Tuna Tagging Programme, with additional funding being promised for work during 2008.

Although tag returns will probably continue for several years, especially for yellowfin and bigeye, an initial resource assessment drawing on the PNG work is likely to be available at the end of 2008. Phase 2 of the project will commence in mid-2008 and will initially operate in Micronesia and possibly Indonesia. Monthly updates on the project can be accessed via the internet at http://www.spc.int/oceanfish/Html/TAG/RTTP2/index.htm.

Simon Nicol is SPC’s Principal Fisheries Scientist (Tuna Biology and Ecology) in the Oceanic Fisheries Programme.