Thailand clam programme making progress

2012-05-21 20:43

Prachuab Khiri Khan - Giant clams don't require much to survive, save a safe spot in the sea.

The big molluscs need sunshine, clean salt water and algae for the photosynthesis that keeps them alive and in the process provides one of nature's most beautiful and varied colour displays on the clams' skin, an underwater wonder for skin divers and snorkelers.

Sex is no big deal. All giant clams are hermaphrodites, emitting eggs one season and sperm the next (but not simultaneously). Daily life consists of sitting around on the sea floor with one orifice open to filter in food and another in the rear to emit waste, eggs and sperm. When danger threatens, they shut up.

Unfortunately, giant clams are easy pickings for fishermen so their numbers have dwindled drastically in Thailand's overexploited seas during the past four decades, along with all other species.

Of the four giant clam species indigenous to Thailand, the Tridacna gigas, the biggest giant, is no longer found, and the Tridacna squmosa, crocea and maxim are all on the endangered list of Cites, the Convention on International Trade in Endangered Species.


In 1992, the Coastal Fisheries Research and Development Bureau in Prachuab Khiri Khan, 200km south of Bangkok, launched a project to bring the Tridacna squmosa back from the brink in the Gulf of Thailand and Andaman Sea.

The project succeeded in getting clams to reproduce in captivity in 1993, but it took a lot longer to successfully restock Tridacna squmosa on Thai reefs, their natural habitat.

"If you put the baby clams back on the reefs in nature, crabs, shrimps and turtles will eat them," said Jintana Nugranad, the Fisheries Department's aquaculture expert who started the giant clam project in Prachaub two decades ago. "Our clams have very thin shells, so that's a constraint for the project."

The solution was to set up "clam gardens". One such, on Koh Tao in the Gulf of Thailand, has collaborated with a local community of divers on the island to make the project work.

"The first year this was done was in 2009, when around 1 000 clams where placed into ten cages in Ao Leuk Bay," said Chad Scott, Project Coordinator of the Save Koh Tao Marine Branch.

Out of the first batch, only 429 survived the first year. The remainder were buried under sand drifts or eaten by predators.

A second batch, supplied in 2010, where moved to a new location, where sand shifting was not a threat. Unfortunately, human predators pilfered some of the clams.


Although giant clams are not a common food in Thailand, they are a popular mouthful among fishermen island communities and occasionally pop up on a restaurant menu in Koh Samui, a popular island resort.

The Save Koh Tao group of divers has now devised better human-proof cages, although poaching remains a threat. Overall, the project is deemed a success.

"After the clams reach a size of about 12cm we transplant them out to the natural reef, so they have been reintroduced to the wild," Scott said. "From there the main threat is the Trigger fish."

"Now we are experimenting with small temporary cages that are placed over the transplanted clam for a period of two to three weeks to allow it to secure to the substrate before being left unprotected," he said.

Similar projects, with varying results, are underway on most reefs in the Gulf and Andaman, Jintana said.

Restocking is obviously more work than breeding and keeping the clams in captivity at Prachuab Khiri Khan. In a tank, the clams just require sunshine and clean salt water with a little fertiliser thrown in once a month to provide algae.

The beautiful colouration of the Tridacna squmosa, which varies from turquoise, purple, deep blue to brown (the brown striped ones are called "Tiger Paws"), makes them an ideal item in an aquarium.

"We are thinking of developing the giant clams for the aquarium trade, but we'd first have to get it off the endangered species list to allow us to trade it commercially," Jintana said.

Past experience with other commercially raised species in Thailand, such as crocodiles, tigers and elephants, has shown that raising exotic animals on farms can create a legal loophole for poachers who continue to hunt wild specimens and then pass them off as commercially, legally raised stock.

"In my opinion, they should not be allowed to collect the animals from the sea but they can come here and get the baby clams from us and raise them to maturity, after which they can sell commercially to aquariums," Jintana said.

  • craig.a.salter - 2012-05-22 11:33

    save the clam

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