A GIANT CLAM STOCK SURVEY AND PRELIMINARY INVESTIGATION OF PEARL OYSTER RESOURCES IN THE TOKELAU ISLANDS
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A GIANT CLAM STOCK SURVEY AND PRELIMINARY INVESTIGATION OF PEARL OYSTER RESOURCES IN THE TOKELAU ISLANDS |
by
R.D. Braley
ACIAR Giant Clam Project
Zoology Department, James Cook University
Townsville, Qld. 4811, AUSTRALIA
South Pacific Aquaculture Development Project,
Food and Agriculture Organization of the United Nations,
Suva, Fiji
July, 1989
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4. Conclusions and Recommendations
A stock survey of the two species of giant clam, Tridacna maxima (fahua nao) and T. squamosa (fahua taka) was carried out between 18 May - 15 June 1989 at the three atolls of Tokelau: Fakaofo, Nukunonu, and Atafu. The field surveys utilised small boats belonging to the Department of Agriculture and Fisheries. The survey team consisted of the author and Fisheries Officer covering all the atolls and Agriculture casual assistants at each atoll. A surface tow method was employed (2 divers, one each side of the boat) to count clams over measured distances. Tows were made around the perimeter of the lagoon reef covering depths up to 12-15m, around patch reefs in the centre of the lagoons, and two tows on the ocean side of each atoll. In addition, reef flat transects were made to determine clam densities over these large shallow areas bordering the lagoon. The following number of tows; reef flat transects were made: Fakaofo - 72;3, Nukunonu - 61;3, Atafu - 35;2.
A preliminary investigation was also made to look at the presence of stocks of the black-lipped pearl oyster, Pinctada marqaritifera in the three atoll lagoons. Here, SCUBA was used to make dives from patch reefs or bommies in the lagoon to a maximum depth of 120ft [36m]. Densities of pearl oysters and spiny oysters (Spondylus sp.) were recorded at several depths down to 100 [30m] or 120ft. No live or dead pearl oyster shells were found in any of the atolls. Densities of Spondylus sp. were high at dive sites in Fakaofo lagoon (32–56/m2) but considerably less at Nukunonu (<1/m2) and Atafu (0–4/m2). The densities at Fakaofo indicate potential competition (for food and settlement) with spiny oysters if pearl oyster introduction is attempted. At Atafu specimens of the small species Pinctada maculata were found.
Stock estimate densities for T. maxima in the ‘lagoon only’ of the three islands were moderately high at Fakaofo (1754/ha), high at Nukunonu (6860/ha), and moderate at Atafu (841/ha). These stock densities are far higher than the very modest densities found in Tuvalu atolls but densities are higher elsewhere in the Pacific. The T. maxima population estimates for the ‘lagoon only’ (excluding the reef flat with its large variability) are: Fakaofo - 1,488,313; Nukunonu - 5,707,468; Atafu - 360,095. Evidence of fishing pressure on the stocks can be seen from the mean size of clams near a village compared with distant parts of the lagoon. It is recommended to establish marine reserves in each lagoon to ensure continued reproductive success of this species.
Stock estimate densities for T. squamosa were extremely low in Fakaofo (0.82/ha) and Nukunonu (0.41/ha) but none were found in Atafu. The population estimates were: Fakaofo - 695; Nukunonu - 345. These populations are at critically low levels for reproduction and at Atafu this species is probably beyond the point of no return. It is recommended to ban the fishing of T. squamosa; to collect broodstock into breeding aggregations where they are protected; to consider the culture of this species in a collaborative project with Western Samoa Fisheries in Apia.
A village questionaire survey was conducted at each atoll to gather personal opinions of men and women in three age groups regarding: the use and availability of clams now and in the past, knowledge of some very basic ‘ecology’ of reef animals, whether they believe there is a need for restrictions on harvesting of clams and if they would like the government to become involved in the culture of giant clams. Clams are consumed on average 1–2×/month/person. The majority (67%) of the people on all atolls believed clams were becoming scarcer. There were never any traditional taboos or conservationist measures with regard to giant clam fishing. A majority (58%) of all people questioned believed there should be some form of restrictions on the harvest of clams. Nearly 100% of the people would like to see the government become involved in the culture of giant clams. Over 60% of the people had never seen a pearl oysters shell (live or dead) taken from the lagoons.
Further recommendations are that: Mr. Mose Pelasio be sent to a training course on giant clam culture in January/February 1990 at the ACIAR-JCU Giant Clam Project; there be a resurvey of giant clam stocks in 1999 using the same sites and method as this report; introduction of pearl oysters may be expensive and establishment of the population may be difficult, despite suitable subtrate in the lagoons; if small or large-scale pearl oyster trials are attempted the stock should come from the Cook Islands rather than Okinawa, Japan.
I gratefully acknowledge the assistance of a number of people in Tokelau and Samoa for their cooperation and support during this survey. Firstly, Mr. Semu Uili of Tokelau Affairs and Mr. Lui Bell, Acting Chief Fisheries Officer - W. Samoa Fisheries) were most helpful in facilitating arrangements for a charter of the W. Samoa Fisheries Research Vessel Tautai Matapalapala (and captain Mr. Stan Weinberg and crew) at short notice [the scheduled boat Wairua was going to be delayed at least 10 days]. I thank Mr. Foua Toloa, Director of Tokelau Agriculture & Fisheries for his support. The eager field survey crew in Fakaofo were Mr. Mose Pelasio (who also accompanied me throughout the whole survey), Mr. Petio Iasona, Mr. Samuelu Manatua, Mr. Eli Lapana, and Mr. Mika Kelesoma.
Also of assistance during the survey in Fakaofo were Mr. Kirifi Kirifi, Agriculture extension officer, Ms. Moana Rimoni, and the Administrative officer, Mr. Iuta Gaualofa, Ms. Luisa Naseri, Ms. Tiresa Galo, and staff of the Tokelau Affairs Office in Apia. The field crew on Nukunonu were Mr. Atonio Eneliko and Mr. Sefo Tioni. The two interpreters for the village Questionaires were Ms. Pulapula Leo and Ms. Vefa Penitito. The field crew on Atafu were extension officer Mr. Etuale Erupi and assistants Mr. Salatielu Filo and Mr. Helu Kalolo. Due to a short stay on Atafu, we were not able to conduct the questionaire survey ourselves so I thank the Agriculture extenstion officer, Ms. Mavaega Epati and her assistants, Mr. Kili Koro, Mr. Kitiona Toloa, and Mr. Enosa Sirila for handling the questionaire survey for us.
The survey was funded by the FAO South Pacific Aquaculture Development Project (SPADP) and Tokelau Affairs/Tokelau Department of Agriculture and Fisheries. I wish to thank Mr. Hideyuki Tanaka, Regional Aquaculturist for FAO-SPADP for his assistance in planning and finance for this survey, and Mr. R. Foscarini for his help. Finally, I wish to thank James Cook University and the Australian Centre for International Agricultural Research (ACIAR) for allowing me to be seconded to FAO-SPADP for this survey.