Following a request for technical assistance from the Tonga Department of Fisheries, SPC Fisheries Scientist (Invertebrates) Kalo Pakoa joined the department’s team in November 2010 to provide technical assistance in this area.

The story of trochus in Tonga begins in the 1990s with its introduction from Fiji Islands as part of an effort to develop a potential new reef fishery. Trochus shell is used as a raw material for buttons and jewellery and is a source of economic activity in many island countries. The resource became successfully established, but its stock status was unknown. In 2006, a baseline assessment of the resource in Tongatapu was completed under the European Union-funded PROCFish (Pacific Regional Oceanic and Coastal Fisheries Development Programme) project.

As recommended in the outcomes of this study, trochus stock in other areas must also be assessed to determine the overall status of the resource and make it possible put in place management measures to grow the resource to a sustainable fishery level. SPC received a request to provide technical assistance to assess the resource in the Vava’u Group. This work was made possible with funding from European Union under the SciCOFish (Scientific Support for the Management of Coastal and Oceanic Fisheries in the Pacific Islands Region) project.

A presentation of the 2006 assessment results was made to Tonga Department of Fisheries by Mr Pakoa, to re-emphasise the proposed recommendations and actions needed in Tongatapu to protect and develop the resource while it was being assessed in other areas. These recommended actions are as follows:

1. Although trochus became established in Tongatapu, its population density is below 500 shells per hectare, which is insufficient to support a sustainable fishery. Fishing therefore is not recommended at this stage.
2. The resource in Tongatapu is sufficient for translocation to other reefs. This should be undertaken without delay.
3. The resource in other parts of the country need to be assessed.
4. The impact of release of juvenile trochus was unclear due to lack of data. Good data collection and record keeping is recommended in future reseeding activities.
5. Trochus is already being harvested for its meat and shell. Awareness and education is a matter of priority for Tonga Department of Fisheries to stop these activities.
6. Enforcement of existing regulations and development of new ones should be undertaken to protect the resource.

These recommendations have been accepted by the Tonga Department of Fisheries, which confirmed that it will focus in the near future on transplantation and awareness and education activities (activities 2 and 5). In addition, these guidelines provide a response to the mounting pressure to officially open the resource for harvest.

The Vava’u assessment survey is a response to recommendation 3. During the training , trochus data were collected. These will be used to determine the status of the resource there. Trochus was introduced to Vava’u in 1992 through transplantation of both of adults and hatchery juveniles from Fiji Islands under the JICA (Japan International Cooperation Agency) project.

We can now confirm that trochus niloticus has also become established in the Vava’u Group. Trochus was recorded at the original adult and juvenile seeding sites and at non-release sites, which indicates that natural recruitment is occurring. Generally speaking, the resource at release sites in Vava’u was less abundant than in Tongatapu, despite the presence of relatively good habitat. One explanation for this is the illegal harvesting of trochus for its meat and shell. Piles of trochus shells were observed in the Village of Taunga, one of original release sites, and trochus shell souvenirs were on sale at the Vava’u local market. Public awareness and education on trochus management is needed urgently.

Resource surveys will be conducted by the Tonga Department of Fisheries team at Ha’apai, Eua and Euaiki in the next two to three months. More time should be given for the resource to mature and become suitable for a fishery.

For more information, please contact Kalo Pakoa, SPC Fisheries Scientist

Photo: Sione Mailau (Fisheries Division) with trochus shell from timed swim survey, Vava’u, Tonga