Culturing Giant Clams in Makogai to Address Sustainability and Conservation
iant clams have formed part of the diet for Pacific islanders coastal dwellers for thousands of years and they continue to be harvested for their meat for both subsistence and commercial purposes.
In many places around the world, giant clam numbers have been dramatically reduced due to over collection for food or souvenirs, and habitat destruction.
To date, nine giant clam species out of 11 are protected under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, giant clams continue to delcine in their marine habitat.
The importance of giant clams in our coral ecosystems cannot be overly emphasised as they play a crucial role on the reefs in which they are found. As large bivalves, they are efficient water filterers, removing excess nutrients that flow into the reefs from land. They also grow very large, dense shells which contribute to the growth of reef structure and provide habitat and settlement for a wide range of other reef animals.
Makogai Mariculture Centre
The Ministry of Fisheries and its development partners have been working hard over the years on reviving giant clam species by producing them at the Makogai Island Mariculture Centre.
Fiji has seven species and these are namely;
T. gigas – Vasua matau, T. derasa- Vasua dina, T. tevoroa- Vasua tevoro, T. maxima – Kata vatu, T. squamosa- Vasua cega, H. hipopus – Teke ni ose and T. crocea- Vasua kabi.
The Mariculture Centre is now focusing on production and rearing of four species namely T. gigas – Vasua matau, T. derasa- Vasua dina, T. squamosa- Vasua cega and T. maxima – Kata vatu.
There are currently eight officers on the island whose main focus is on hatchery production. Their work covers several phases which includes production and rearing from the land-based hatchery to ocean nurseries.
The production processes are holistic as it covers biology and environmental requirements, hatchery management, broodstock acquisition and husbandry, Induce Spawning, egg and sperm collection, fertilization, counting, larval rearing and nursery grow out.
The success of rearing hatchery produced giant clams are determined from the appropriate selection of brooders and its surrounding environmental parameters.
According to Director Fisheries, Ms Neomai Ravitu, the application of this natural environment to land based setup can be quite challenging at the Mariculture Centre.
“The submersible pump is set up for the circulation system of saltwater which is used for spawning, rearing and grow-out of giant clams. Through this process the officers provides a means for giant clams to acquire food supply through natural photosynthesis process, other than injecting formulated feed,” said Ms Ravitu.
“This enables maximum survival rate of seedlings from the spawning to its grow-out stages.
“The application of natural process in the hatchery based facility allows them to adapt in designated ocean nurseries which are then prepared for reseeding activities in Fiji’s reefs.”
Giant clam spawning involves fertilization of eggs from selected brooders which hatch within a period of 12 hrs. It takes 2-3years for giant clams to reach its adulthood.
Broodstock Management
Broodstock management includes the collection of wild brooders from the reefs around Makogai Island. Healthy brooders are selected and taken to the hatchery for spawning.
“The brooders especially the T.gigas have heavier body masses, which needs more manpower in transferring them from the ocean nursery to the land-based hatchery,” adds Ms Ravitu.
The nursery grow-out is the most important phase on the island where juvenile clams are relocated from the land-based hatchery to the ocean nursery for normal feeding and acclimatization to a more natural environment.
“Officers take great care in brooder selection especially in identifying the most suitable broodstock based on the best genetic fit which is considered to be a high priority for both restocking and mariculture of giant clams.”
“The identification of the genetic/environmental interactions of Tridacana species are considered a high priority for the effective management of wild and cultured clams.”
Restocking and conservation reefs with Giant Clams
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The Ministry of Fisheries have been receving numerous requests from communites for restocking of their reefs and the Research Assessment and Development (RA&D) Division of the Ministry is now looking at strategies on best site selection whilst incorporating oceanography and environmental parameters and also setup of appropriate designed infrastructures.
Ms Ravitu says that this is to ensure the provision of an enabling environment for the maximum production and survival of artificially produced giant clams.
“The distribution of juvenile clams in the communities will be determined by the availability and sizes of equipment and materials that the ministry have.
“Currently, the Ministry of Fisheries is providing cages and juvenile clams for reef reseeding in some communities whilst the sub adult clams are only used for research purposes.”
“Many rural communities have expressed their interests in the past and have been assisted.
The giant clams reared at the hatchery have been distributed to many of Fiji’s marine protected areas (MPAs) which are managed by the local communities and hotels.”
Some of the communities assisted with the reseeding program include; Serua Island, Kadavu, Vanua Balavu, Lakeba, Kiuva, Namara, Navakavu and Naocobau, Ovalau, and Motoriki.
Through a Memorandum of Understanding that was signed in 2019, the Ministry of Fisheries and the Fiji Hotel and Tourism Association (FHTA) have been working together in addressing matters of common concern in the context of natural resource management and its long-term sustainability.
The five year agreement and partnership enhances cooperation in the area of research and information exchange for the fisheries sector economic planning and sustainable fisheries development, conservation and management, sports or recreational fishing.
A total of twenty-four resorts and properties have expressed their interests of venturing into species management or marine ecosystem initiatives through the Fiji Hotel and Tourism Association (FHTA).
The Ministry has visited and inspected around 19 resorts since August 2019 and this is done to identify viable sites with suitable conditions to establish marine protection projects requested by resorts, which mostly involve giant clam farming.
Last year, five hotels have had their MPAs reseeded with juvenile giant clams and are namely;
Fiji Marriott resort at Momi
Octopus Resort,
Barefoot Manta Bay Resort in the Yasawa Group of islands, Treasure Island Resort and
Navini Island Resort in the Mamanuca group.
Other resorts and private islands include; Mago Island, Kaibu Island, Leleuvia Resort, Toberua Resort and Outrigger Resort.
As well as being a tourist drawcard, community interest in restoring giant clams to their reefs is high and coastal communities around the country are attesting to a healthier marine ecosystem where giant clams are living.
Giant clams offers more towards the health of our ocean as well as economic returns to the communities and the ministry is working towards ensuring that the reseeding program is replicated around the country.
Work in progress include the development of management plans, governance framework and completing policies across key agencies.
The Ministry is also helping to drive Government’s efforts on blue economy initiatives.