Map 1
Map 2
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Trochus niloticus (Mollusca: Gastropoda) is commonly known as the topshell or trochus shell and by various names in the countries where it occurs naturally. It is a large, conical-shaped, marine gastropod (snail) of shallow tropical reefs that can attain a size of over 120 mm, measured across the base. The shell of trochus has external mottled red-green and white bands and a thick inner layer of mother-of-pearl (nacre), which makes it valuable for manufacture of jewellery and buttons for highlypriced garments.
Global Demand
The current global demand for trochus shell is estimated at 7,000 tonnes annually, worth about A$50 - $60 million. Due to an increasing value and demand for shell, trochus stocks on many reefs in Australia and the Indo-Pacific have been over-exploited. This trend has fuelled much research on mass production of juveniles in hatcheries and restocking techniques which aim to provide methods for stock enhancement.
Distribution
Trochus are found in two tropical regions of Australia. The first region includes the Great Barrier Reef and the Torres Straits Islands, off the coast of north Queensland; this region supports a large and productive trochus fishery. The second region is located in Western Australia (WA) where trochus are found on coral reefs of the Buccaneer and Bonaparte Archipelagos in the Kimberley and offshore at Rowley Shoals, Browse Island, Scott Reef, Seringapatam Reef, Ashmore Reef and Cartier Island (Map 1).
Local Community Access
On the remote offshore reefs of WA, trochus are fished by Indonesian fishers under a Memorandum of Understanding (MOU) signed between the Republic of Indonesia and the Commonwealth of Australia in 1974. Under the MOU, only sailing vessels are allowed into the zone. On inshore reefs, trochus are collected by the Bardi Aboriginal community from One Arm Point and other communities living along the coastal region of King Sound. The export of the shell provides a valued income for these communities, while the meat is eaten locally.
Annual Harvest
Annual harvests in recent years declined drastically to less than 15 tonnes, compared to about 50 tonnes a decade ago and 135 tonnes in 1980. A great deal of applied research, on producing juveniles and enhancing trochus fisheries, has been conducted during collaborative projects involving Australian and overseas scientists. This is reflected in the reading list, particularly a major conference proceedings that includes research papers by numerous authors (edited by Lee & Lynch, 1997) and a new hatchery manual (Crowe et al ., in prep).
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