1.1 TOKELAU PHYSIOGRAPHY AND HISTORY
The Tokelau group of islands are comprised of three coral atolls located between 8–10°S and 171–173°W. The Tokelau group is 500km north of W. Samoa, 450km south of atolls in the Phoenix group of Kiribati, 500km west of Pukapuka in the Cook Islands, and 650km east of the Tuvalu Islands. The tiny coral island of Swains which has historical connections with Tokelau but is presently under the juristiction of American Samoa is 175km south of the largest populated atoll in Tokelau, Fakaofo. Fakaofo is 65km from Nukunonu in the west and 150km from Atafu in the north.
The three atolls are all of the closed variety with high reefs circling moderate size lagoons. Due to the lack of deepwater passages few ships attempt to anchor off the atoll reefs with their steep dropoffs to deep ocean water. There are small blasted passages halfway across the reef flat to the ocean side of the populated islets to facilitate unloading/loading of passengers and cargo. Very shallow natural channels are present but are quite hazardous to cross. The estimated land and lagoon areas, respectively, are: Fakaofo - 2.5km2 and 48km2; Nukunonu - 2.6km2 and 95km2; Atafu - 2.0km2 and 15.5km2. The islets are only about 5m above sea level and composed of coral and foraminiferan sand and rubble. The SE trade winds blow from April to October and more varying northerly winds from October to April. The average temperature of air and sea is about 28°C and the average annual rainfall is 200cm [highest fall between October and March]. Severe cyclones hit Tokelau in 1846, 1914, 1966 and 1987.
Atafu, Nukunonu and Fakaofo were first sited by Europeans in 1765, 1791, and 1835, respectively. In 1865 the Peruvian slave traders kidnapped a high percentage of the islanders and during the 1860s Christianity began to become established. The group came under British Protection in 1877 and was annexed in 1916 (then known as the Union Islands). In 1925 the responsibility for the islands was transferrd to New Zealand. Since 1948 they have been formally a territory of New Zealand. About 750 people live on Fakaofo, 500 on Nukunonu and 600 on Atafu today. Nearly twice as many Tokelauans live in New Zealand or elsewhere.
The island governments are controlled by a Council of Elders (taupulega), a Village Commissioner (faipule), a Mayor (pulenuku), and an Administrative Officer for the public service workers.
1.2 GIANT CLAM CLASSIFICATION AND SKETCH OF BIOLOGY
Seven species of giant clam exist today though fossil species go back to the Eocene (65 mil. yr). The species are described and illustrated along with maps of their known distributions in Appendix 1. It is possible that an eighth species has been found in the Lau Group of the Fiji Islands, the so called ‘Tevoro’ clam, but more live specimens are required before this can be confirmed and described (Lewis and Ledua, 1988). The seven known species, listed from the largest to the smallest in size are:
Tridacna gigas
Tridacna derasa
Tridacna squamosa
Hippopus hippopus
Hippopus porcellanus
Tridacna maxima
Tridacna crocea
The recent great interest in culture of giant clams has been concentrated on the largest 5 species, although the Japanese have made recent efforts at culturing T. crocea in Okinawa (Murakoshi, 1986). The ACIAR (Australian Centre for International Agricultural Research) - JCU (James Cook University) Giant Clam Project has concentrated on T. gigas in North Queensland [Orpheus Island Research Station - OIRS], T. squamosa and T. derasa in the Fiji Fisheries component of the ACIAR Clam Project, and H. hippopus and H. porcellanus in the Philippines component. The MMDC (Micronesian Mariculture Demonstration Center) in Palau concentrates on the culture of T. derasa and the new ICLARM CAC (Coastal Aquaculture Centre) in the Solomon Islands is concentrating on T. gigas. There are two private ventures in North Queensland which are also working on the culture of T. gigas.
The most unique evolutionary development in giant clams was the symbiotic relationship formed with a microscopic dinoflagellate algae, Symbiodinium microadriaticum. This algae, termed zooxanthellae, is the same species (but a different variety) which inhabits the cells of coral polyps. However, in clams the algae lives freely inside the blood passages. Vast numbers of algae collect in blood spaces just under the surface of the highly coloured mantle tissue of the clam. This mantle surface is exposed to sunlight and thus the symbiosis requires that giant clams live in shallow (<20m where the water is clear) tropical seas. The algae photosynthesise in sunlight and the simple sugars and other photosynthetic products are used directly by the clams. It appears that clams can obtain almost 100% of their dietary needs from the zooxanthellae relationship.
Giant clams naturally grow amongst coral reefs although large individuals may sometimes be found on sand, probably an example of clams growing up in the protection of a thicket of branching Acropora sp. coral and at some point a storm or other perturbation destroyed the branching coral thicket and left the clam on bare sand. Clams live from the intertidal zone down to about 20m but in very clear water the depth may be greater for T. derasa and T. squamosa. At these depths the light levels may be so limited that growth and reproductive condition of these individuals may be poorer than their fellow clams living at optimal light levels.
Reproduction in giant clams was first investigated for biological interest (Stephenson, 1931; Wada, 1954) but recently reproduction and larval biology have been studied for the mariculture potential (Beckvar, 1981; Gwyther and Munro, 1981; Heslinga et al., 1984; Braley, 1986; Crawford et al., 1986; Braley et al., 1988). The adult clams are generally simultaneous hermaphrodites, thus producing both sperm and eggs. Breeding may be throughout the year at low latitudes but it is seasonal, restricted to summer months at higher latitudes within the tropics. The release of gametes takes place with expulsions through the excurrent siphon. In natural populations, gamete release may trigger other clams in close proximity to commence gamete release as well (Braley, 1984). This may lead to spatially clumped groups of clams spawning together as ‘reproductive units’. It is essential then that to promote maximum successful spawning and fertilisation of eggs the broodstock clams be in close proximity (relatively high density).
The eggs of giant clams are about 100um (0.1mm) diameter.
The eggs of giant clams are about 100um (0.1mm) diameter. Adult clams of the smaller species may spawn 5–30 million eggs but adult T. gigas may spawn more than 500 million eggs (observations from hatchery work at Orpheus Island Research Station, North Queensland, Australia). The embryos develop and a trochophore larvae hatches at about 12–15hr. This larvae, still without a shell, swims in the sea and develops into a veliger larvae by 40–48hr. Once the larvae has become a veliger it has a double shell and hinge and it will continue to add to its shell growth as its soft body parts increase in size. This larvae has a swimming organ which it uses to also filter single-celled algae (phytoplankton) from the seawater. The larval swimming period is about 1 week after which the larvae settles to the bottom (on dead or live coral rather than sand for survival) and can use a foot to crawl around seeking the most suitable site to settle. The settled larvae has to develop gills, obtain the special dinoflagellate algae (zooxanthellae) for its juvenile and adult symbiosis and go through other biochemical changes over the next 2 weeks before it can be considered a juvenile clam [at this stage it would still be only 250–300um, 0.25–0.3mm diameter]. Growth in the first six months is slow and even after 1 yr. the shell length may be 2–5cm. In the largest species, T. gigas, growth is relatively rapid after 1 yr., resulting in 10cm at 18 mo. and 22cm in 3 yrs. Growth rate studies indicate T. gigas may be able to reach 70cm shell length in 15 yrs. (Gwyther and Munro, 1981). The other species reach only 25 cm in 5–10 yrs.
1.3 GIANT CLAM USE AND EXPLOITATION
Giant clams have always been part of the staple diets of South Pacific islanders. They are eaten raw, marinated in lime and served with coconut cream, boiled in coconut cream with or without curry, sun dried or salted, or prepared with vinegar. In Singapore, Taiwan, Japan and China there is considerable demand for the adductor muscle of the giant clam which is valued at similar prices to scallop adductor muscle.
Large clam shells are used as pig feeding troughs in many islands. Thick circles of clam shell were cut as a base for fine tortoise shell carvings in the Solomon Islands. Clam shell also makes good lime for betel nut when it is burned. In the Philippines, clam shells are used in handicraft items, and large whole shell pairs are sold for a high price.
Giant clam stocks (mainly T. gigas and T. derasa) in the Pacific region began to be exploited aggresively by Taiwanese fishing boats in the 1960s so that by the mid-1970s to early 1980s the alarms were being raised by concerned fisheries scientists (Pearson, 1977; Hirschberger, 1980; IUCN, 1983; Dawson, 1984). The Taiwanese poaching now has slowed down significantly but this may be related as much to the extinction of stocks from accessible areas as the political pressure from Australia and other nations. Stocks of the largest species, T. gigas, have been most heavily damaged so that its former range throughout Micronesia and down to Fiji has nearly contracted to an area surrounding the Coral Sea (Solomons, Papua New Guinea and Australia's Great Barrier Reef). The largest natural populations exist on the north-central Great Barrier Reef where exploitation has been minor (Braley, 1986). Extinctions of other species around some islands may be purely due to overfishing by islanders as their populations have increased and with the introduction of motorboats and better diving aids. An example is the demise of H. hippopus in W. Samoa, Fiji and Tonga in recent times.
1.4 PEARL OYSTERS
The three most important commercial species of the pearl oyster genus Pinctada are P. maxima (gold-lipped pearl oyster), P. margaritifera (black-lipped pearl oyster), and P. martensii (Japanese pearl oyster). The gold-lip is found only in the western Pacific, Australia and the Indo-Malay region. The black-lip is more widespread and is found across the Indo-Pacific to French Polynesia. In the northern Cook Islands of Manihiki and Penrhyn the densities of the black-lip are 6.7 / 100 m sq and 3.1 / 100 m sq (Sims, 1988). Densities and stocks of this oyster are even higher in Takapoto lagoon in the Tuamotus (Intes et al., 1986) but these are the highest densities recorded from any other Pacific atoll lagoons. Black-lipped pearl oyster was used for making Tokelau pearl shell lures for traditional tuna fishing (Gillett, 1985). The shells are now rarely found in the lagoons of Tokelau.
Black-lipped pearl oysters are generally male or female but they may change sex throughout life. These oysters mature in 2 years but most are still males at this stage and take 5 years to reach an even sex ratio, which makes management of stocks very important (Sims, 1988). There are two spawnings in the year (Aug.-Sept. and Feb.-Mar.); larvae swim for 3–4 weeks before settlement (Coeroli et al., 1982).
The current price for cleaned grade-A shell is US$5.50/kg. Commercial pearl farming is being carried out with the black-lip in French Polynesia and Manihiki lagoon in the Cook Islands. The gold-lip is the basis for commercial pearl farming in Australia and in Papua New Guinea. Disease problems have plagued the culture of both species at various times due to high densities in culture and transhipment from other areas. Sims (1988) called assist the newly developing industry and assure that the natural stocks, which are declining from overfishing in all lagoons will not reach critically non-renewable levels.
There have been several consultants who have made brief visits to Tokelau to, among other things, assess the feasibility of introducting black-lipped pearl oyster to Tokelau lagoons (van Pel, 1958; Hinds, 1971; Laboute, 1987). In 1958 van Pel made a visit on behalf of SPC. He incorrectly identified the giant clams as T. gigas and Hippopus hippopus but noted the presence of numerous thorny oysters (Spondylus sp.). He found no pearl oysters at Fakaofo but noted a few were occasionally found by people and suggested the lagoon would be good for culture of P. margaritifera. He did not visit Nukunonu but in Atafu he saw one live P. margaritifera which someone was keeping on the reef. He also noted 3/8“-1 3/16” P. maculata in the lagoon fixed on table reefs near the surface and a small wing pearl shell (Family Isognomontidae) common in the lagoon. He suggested two sites at each atoll where pearl oysters could be introduced. Hinds (1971) made some deep dives with Scuba (200ft) in the lagoon at Fakaofo but found no pearl oysters. He noted that 2 specimens of black-lipped pearl oyster were found in Atafu lagoon in the past 2 years. Hinds suggested that a transfer of mother of pearl was not a straight-forward affair as there had been problems between different lagoons in French Polynesia in survival/growth. He suggested that 5000 live shells be transferred from Tonga or the Cook Islands in a suitable vessel with holding tanks and circulating seawater. A spat collection system using underwater pipe frames was suggested for initial stages of such a venture. Finally, Laboute (1987) found it surprising that Fakaofo lagoon, with it similarities to those of French Polynesia, had no P. with it similarities to those of French Polynesia, had no P. margaritifera or P. maculata and went on to suggest that the lagoons would be suitable for trials to establish P. margaritifera. He did, however, mention the remarkable abundance of Spondylus (aff. varius) from 5–50m deep.
1.5 BACKGROUND OF THE SURVEY
Mr. Foua Toloa, Director of Agriculture and Fisheries, Tokelau expressed interest to me in having a survey of giant clams conducted in Tokelau while at the SPC Inshore Fisheries Workshop in Noumea, March 1988. At that time I was organising with the Chief Fisheries Officer of Tuvalu, Mr. Elisala Pita, and Mr. H. Tanaka of FAO-South Pacific Aquaculture Development Project to plan for a giant clam stock survey in Tuvalu in May 1988. I was asked by Mr. Tanaka in February 1989 if I would be available to conduct a stock survey of giant clams and a preliminary study of pearl oyster stocks.
The Terms of Employment as a Consultant for FAO included the following description of duties:
Carry out a stock survey of giant clam and a preliminary stock study of black-lip pearl shell in Fakaofo Island, [and Nukunonu and Atafu Islands if possible… my addition here in brackets from the discussions we had]
Make assessment of the present state of giant clam fishing intensity in association with socio-cultural features of islanders and study mechanisms of traditional reef resources conservation system taken by islanders, if existent,
Make recommendations on necessary measures for maintenance and or propagation of giant clam and black-lip pearl shell resources with description of future steps by due consideration of existing socio-economic aspects, and
Produce a report of all findings.
