Reef re-seeding research of the topshell, Trochus Niloticus in northern Australia, eastern Indonesia and the Pacific

• Indonesian Institute of Sciences, Indonesia
• Fisheries Department, Vanuatu
• University of Pattimura, Indonesia
• Universitas Nusa Cendana, Indonesia

Australia, Indonesia and Pacific Islands nations supply up to 90% of world demand for trochus shell, about 7000 tonnes a year. Increasing demand in recent years for shell for high quality buttons, jewellery and other uses has resulted in rapidly rising prices and concerns about over-exploitation of the fishery.
All nations involved in the trade were concerned about falling production and increasing scarcity of trochus. Indonesia was worried about over-exploitation of the trochus grounds where communities have fished for trochus for centuries. Trochus was also one of the most important fisheries in Vanuatu.
Western Australian production is centred on King Sound, near Broome. Concerned at dwindling trochus populations, Aboriginal communities of the Sound sought assistance from the Northern Territory University, which had developed expertise in hatchery production of juveniles.

This project, bringing together researchers from Australia, Indonesia and Vnuatu, was designed to establish the feasilility of maintaining sustainable trochus fisheries in northern Australia, eastern Indonesia and Vanuatu through reseeding with hatchery-produced juveniles.

The first objective was to transfer the production hatchery technology developed at the Northern Territoty University to the participating institutions. The second objective was to develop strategies for seeding juveniles on selected coral reefs.

Transfer of production hatchery technology from the Northern Territory University to the participating institutions involved training staff and establishing small pilot hatcheries in each country.

Laboratory and field studies commenced to develop strategies for seeding juveniles on selected coral reefs. Project members determined the factors that charactise a good site for trochus reseeding; established the optimum size of trochus for reseeding nd the optimim stocking density; identified the principal competitor and predator species, and developed strategies for enhancing the survival of the juveniles after reseeding.

Simple and effective hatchery techniques for spawning and rearing trochus were developed, refined and transferred. This was a significant achievement.
Studies to develop strategies for seeding juveniles on selected coral reefs in Ambon and Kupang (Indonesia), King Sound, Western Australia and Vanuatu led scientists to conclude that the release of unprotected juvenile trochus (6-25 mm) is unlikely to be an effective means of enhancement, and also there is likely to be no common solution to the problem of seeding trochus on reefs in Australia, Indonesia and Vanuatu.
Late success achieved with high survival for caged trochus in Vanuatu and Indonesia and the success of brood stock translocations suggest that development of site-specific solutions based on the results of the present project would be possible, and should lead to the desired outcome of enhanced trochus fisheries.
Predation appears to be the major influence on survival of seeded trochus, but there is evidence that the types of predators and the magnitude of their effects vary among countries. It seems likely, therefore, that local solutions to the enhancement problem will be required. Possible future research should focus on larger spatial scales, further development of enclosures for small trochus, fisheries closures and broodstock manipulation, with country-specific differences in the relative weight placed on these lines of work.. This should be linked to the development of appropriate management regimes.
The project was extended to enable a further two years of joint research involving Aboriginal communities and the Fisheries Department of Western Australia, Vanuatu Fisheries Department, and LIPI in Indonesia to develop site specific reseeding/culture strategies.
As a result of the trochus hatchery and reef enhancement work conducted since 1993, the Aboriginal and Torres Strait Islander Commission (ATSIC) decided to assist the incorporation of the Kimberley Aquaculture Aboriginal Corporation (KAAC) to support aquaculture development in the Kimberley. In 2000, with some extra assistance from the West Australian Government, ATSIC funded KAAC to proceed with the construction of a $3.2 million multi-species hatchery in which to produce juvenile trochus to enhance its depleted reefs. KAAC intends to reseed trochus depleted reefs in 17 aquaculture farm licensed sites across the Kimberley region.
In Vanuatu, experiments conducted on the islands of Tanna and Aniwa were highly successful, demonstrating that the relocation of just 163 broodstock to both island sites rapidly enhanced local recruitment of juvenile trochus. There appeared to be a high degree of self-recruitment at both sites, and the scientists concluded that broodstock seeding has the potential to generate a larval supply of trochus and also to enhance conditions for attracting larval trochus from the water column to settle on the reef.
In the Kimberley Region of WA, in contrast to the situation in Vanuatu, juvenile reseeding on sites in the Dampier Peninsula led to a significant increase in reseeded sites. However, broodstock seeding at sites on the west coast of Dampier Peninsula, where trochus do not occur, and Sunday Island where they are depleted, did not appear to increase subsequent recruitment of juveniles.