Replenishing sea cucumber stocks, rearing sandfish in captivity in the Pacific and Vietnam
Lowly and humble are words often paired with sea cucumbers. However, the dried flesh of these animals, known as trepang or beche-de-mer (literally sea grub) is very popular in Asia, especially in China, Taiwan, Japan and Southeast Asia, where it is a real delicacy and is used to thicken and flavor soup.
Trepang is also a traditional Chinese medicine and has been used for thousands of years to treat arthritis. It is also used to treat high blood pressure, muscle pain and inflammation (pain and swelling), and to boost the body's ability to fight infection and improve muscle strength.
Related to the starfish, sea cucumbers have a soft, wormlike body and range from a few centimeters to 90 centimeters in length. Unlike the starfish, however, they have no arms but use a cluster of tube-like feet around their mouth to gather food. This coral reef invertebrate lives on the seafloor and is a slow-moving, almost inert animal. To defend themselves, they can eject their viscera and parts of their respiratory system through the anus to distract attackers. They later regenerate the missing parts.
Because they live in shallow water and are so easy to collect, sea cucumbers are very easy to overfish. And, due to buoyant demand, populations from East Africa and India to Southeast Asia and the Pacific have been exploited to near extinction, leaving behind disrupted and impoverished environments.
There is therefore an urgent need to return depleted fisheries to sustainability and ensure future supplies in order to help coastal communities out of poverty. Sea cucumbers are a valuable export commodity, with the highest valued species, the sandfish ( Holothuria scabra ), commanding as much as US$75 per kilogram.
WorldFish is working to rebuild depleted stocks in New Caledonia and the Solomon Islands in the Pacific. The poor island states of the Pacific have among the highest population growth rates in the world. The population of the Solomons, for example, is likely to double to one million within 20 years.
The program in New Caledonia aims to develop technology for rebuilding depleted stocks by culturing and releasing juveniles into the wild. WorldFish has successfully hatched and reared thousands of juvenile sandfish in New Caledonia . It is currently identifying the best strategies for releasing hatchery-produced sandfish juveniles in the wild so they survive in high numbers. Genetic studies are carried out to ensure that the hatchery-produced juveniles are released into populations genetic make-up similar to that of their parents . The program is funded by the Australian Center for International Agricultural Research (ACIAR).
WorldFish is also assessing the potential to grow sandfish with shrimp in earthen ponds in collaboration with the French Research Institute for Exploration of the Sea (IFREMER) in New Caledonia . Initial results are promising. Among the findings: that juvenile sandfish can grow with small shrimp and do not affect their growth or survival. Further studies are needed to test the co-culture at various stages in the shrimp culture cycle. Sandfish can provide a by-crop for shrimp aquaculture and an environmentally friendly approach because they eat waste products from the shrimp.
In the Solomons, WorldFish is developing sustainable, community-based management schemes in collaboration with ACIAR and the islands' Department of Fisheries and Marine Resources. Overfishing has depleted stocks and production is now less than one-tenth that of the early 1990s.
The schemes call for participation by all stakeholders -- fishers, buyers and government agencies. Conservation may only be successful if it involves local people who have planned and carried it out for themselves, and in the full knowledge that they will be the beneficiaries.
WorldFish is also helping islanders obtain better returns for their products in the world market. Meanwhile, alternative ways of making a living are being developed to help the islanders, including seaweed farming and the culture of giant clams and hard corals for the aquarium trade.
The islanders are now more willing to seriously consider reducing their sea cucumber catches, knowing that what they leave behind will not be taken by somebody else. There has also been a decline in the illegal harvesting of sea cucumbers.
Harvesting the sea cucumber has been part of the Solomons' culture for at least 200 years. It is a traditional activity for women who walk along the reefs at low tide. It helps pay for food, medicine, as well as the school fees. Nearly half of the families in some villages rely on the fishery.
Rebuilding the sea cucumber fisheries is also important to maintaining and improving the health of the underwater ecosystem. Sea cucumbers are very important bioturbators. They are the vacuum cleaners of the reefs. They help maintain the seabed by sucking up mud and debris to extract the nutrients. In this way, the sea cucumbers aerate sediments and recycle nutrients in a similar way to earthworms. And they may also form important links in marine food chains. They produce vast numbers of larvae that drift in the sea, forming part of the zooplankton that sustains a vast array of other animals.
WorldFish has also successfully hatched sandfish in Vietnam. Working with the country's Regional Institute for Aquaculture No. 3, the WorldFish project was the first in the world to produce sandfish in captivity. The project was completed in 2003, but the Vietnamese institute continues to rear juvenile sandfish to supply shrimp and lobster farmers battling disease and pollution.
Shrimp and lobster farming has seen explosive growth in the past two decades, providing jobs and livelihood for over 200,000 people. However, disease has wiped out many shrimp farms and the coast is now dotted with abandoned ponds. And over-intensive farming, coupled with runoff from development in catchments, has resulted in too much nutrients going into aquatic systems, triggering explosive growths of algae and eutrophication in lobster farms. This occurs when all the oxygen in the water is used up when the algae decompose, suffocating aquatic life. Some algal blooms also generate dangerous toxins.
The hatchery-reared sandfish are valuable in a number of ways:
- They are a source of much-needed income to shrimp farmers who rear them in fallow ponds.
- The growing of sandfish with shrimp promises to make shrimp farming at lower densities more sustainable. The sandfish can make the environment healthier by ingesting bacteria and algae that cause anoxic conditions, lower water quality and generally pave the way for disease-causing pathogens to flourish.
- Farmers are experimenting with placing sandfish in pens below lobster cages to suck up waste feed lost through the cages to reduce nutrient levels. The sandfish could also prove to be a viable commercial crop in itself.
WorldFish's work in the Pacific and Vietnam has established it as the world's leading authority on the hatchery production of tropical sea cucumbers. The benefits of its work in these places will spill over to other parts of the world. The Philippines and Egypt , for instance, have requested advice and training in sea cucumber rearing to replenish severely overfished stocks.
