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Home , Anaa, Fakahina, Fangatau, Giant clam, Pukarua, Raivavae

SPECIAL TRAITS AND PROMISES A SPECIAL CONTEXT The invertebrate popula- OF THE GIANT CLAM ( tions of the eastern Tuamotu Islands include large numbers of MAXIMA) IN giant clams, a vital protein and cultural resource for these atolls. Each island has its own name for INTRODUCTION giant clams, which are most com- Antoine Gilbert1, monly called pahua in French Naturally drawn to the sea, George Remoissenet2, Polynesia as a whole, and kohea Polynesians are traditionally fish- Laurent Yan3 and in the eastern Tuamotu Islands. 4 ers and lagoon or coastal seafood Serge Andréfouët Giant clam meat is eaten raw, consumers. With an increasing cooked or sometimes smoked population in the Fisheries Department (SPE) will and dried. (Fig. 1) and a corresponding make it possible to sustainably increase in the demand for lagoon develop and manage the artisanal Tridacna maxima is still abundant seafood products, certain islands fisheries sector. Since 2001, the SPE in French Polynesia, although have diversified their economic has funded and participated in this abundance is uneven. It activities to meet the demand for efforts to manage, exploit and reaches outstanding levels (Tab.1) seafood. In some French Polynesian repopulate certain echinoderm in some of the islands, fishers are frequently seen and mollusc species in French ( and ) and in the collecting and cleaning giant Polynesia's and reefs. closed atolls of the eastern clams on site before draining and Giant clams (Tridacnidae) are the Tuamotu Islands, including freezing them for export to , primary molluscs of commercial , , , or exchanging them when ships interest. Tridacna maxima is the only , , , and arrive. In fact, many artisanal fish- one of the eight tridacnid species (Salvat 1972; Andréfouët eries have developed over the past (Rosewater 1965) found in French et al. 2005; Gilbert et al. 2005; 30 years, targeting both fish and Polynesia. Because of the popular- Gilbert et al., in publication). invertebrates; an activity that has ity of its meat, Tridacna maxima is been boosted by the arrival of covered by a programme funded In contrast to the giant clam’s ships with cold storage rooms entirely by the second phase of the abundance and dominance in the and, more recently, by inter-island /French Polynesia develop- lagoons of these islands, its abun- air transport. ment contract. dance in other French Polynesian

French Polynesia’s geographic distribution is wide and sparse (118 islands scattered out over an EZZ of some 5 million km2), and its population spread is also very uneven: 87% of the population lives in the Society Islands with 75% on just two islands in the Windward group: Tahiti and Moorea (Anon 2002a). Modern transport methods, however, have made it possible to reduce the isolation of certain French Polynesian islands and have opened the door to new forms of inter-island exchange.

Recent work by the Ministry of Marine Affairs (MER) and the Figure 1: Demographic changes by island group from 1971 to 2002 (source: Institut Pacifique de Polynésie française.

1 Antoine Gilbert: Institute of Research for Development, Arue, Tahiti, French Polynesia Tel: (689)50-62-00, Fax: (689)42-95-55, Email: [email protected] 2 Georges Remoissenet: Fisheries Department, BP 20, Papeete Tahiti 98713, French Polynesia 3 Laurent Yan: BP 1658 Papeete, Tahiti, French Polynesia 4 Serge Andréfouët: Institute of Research for Development, BP A5, 98848 Noumea, New Caledonia

44 SPC Fisheries Newsletter #118 – July/September 2006 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA

Table 1: Mean density (ind/m2) on Moorea (Society Islands), Tubuai, Raivavae (Austral Islands), , (western Tuamotu Islands), Reao, Pukarua, Fangatau and Tatakoto (eastern Tuamotu Islands)

Moorea Takapoto Anaa Reao (pers. Pukarua Fangatau Tatakoto Tubuai Raivavae (Laurent, 2001) (Laurent, (Laurent, observ.) (pers. (Gilbert et (Gilbert et (Gilbert et (pers. 2001) 2001) observ.) al., al., al., observ.) submitted) submitted) submitted)

Area and/or number of samples 20 000 m2 1150m2/6 2735m2/14 3200m2/303 1305m2/173 86m2/343 70m2/281 2950m2/326 5485m2/313 Sampling method PCQM*** T* T* T* T* QSM** QSM** T* T* Mean density (ind/m2) 0.035 0.14 0.02 8.15 13.06 44.09 87.37 2.53 1.31

* Transect Sampling Method ** The samples are located in the live giant clam strata (for more details please refer to the methodology described in Andréfouet et al., 2005) *** Point Centered Quarter Method lagoons is much lower (Tab. 1), SPE has had to respond to the recommend management meas- and certain lagoons are currently concerns of mayors and inhabi- ures, notably in , Micro- experiencing declines, sometimes tants of the islands involved. nesia (Hardy and Hardy 1969), significant, in their populations. Against this background, several One Tree Island, While this is in part due to natural studies have been carried out (McMichael 1974), Rose Atoll, causes (Addessi 2001), the since 2001. One study was a local American Samoa (Green and increase in fishing pressure, in market survey conducted by a con- Craig 1999), Milne Bay Province, response to the growing human sulting firm (Pacific Consulting). A Papua New Guinea (Skewes et al. population pressure, is certainly a range of other studies and sur- 2003), and Reao, Takapoto and major cause. While in the past, veys were carried out by various Anaa islands in French Polynesia large numbers of giant clams research institutions: studies on (Salvat 1971, 1972, 1973; Richard could be found in the lagoons of genetics (École Pratique des 1977, 1982, 1989; Laurent 2001). the Society Islands, they are Hautes Études-French National becoming increasingly scarce as Centre for Scientific Research), In 2003, remote sensing was used they continue to be a popular natural stocks (Institute of to estimate giant clam stocks in species at the Tahiti market. With Research for Development and French Polynesia (as part of the about 50 tonnes of meat marketed the University of French SPE’s giant clam programme: each year on this island (Anon Polynesia), natural stock dynam- Andréfouët et al. 2005), using a 2002b), this "new" financial ics, a fisheries survey (Institute of refined version of the method ini- resource provides significant and Research for Development and tially proposed by Green and direct income to the communities the French National School of Craig (1999). Nowadays, a rising on the outer islands. Income gen- Agricultural Sciences in Rennes), number of studies on tropical erated from the giant clam market a survey on fishers and related coastal systems ( reefs, man- for all fishers has been roughly populations (University of French groves, sea grass beds: Green et estimated to be between XPF 20 Polynesia), and a study on har- al. 2000) include high resolution and 25 million annually. This is a vesting techniques, , remote sensing, particularly for fairly significant supplement to transport and reseeding (SPE). inventories of commercially sen- traditional resources, which are sitive species, or invasive often limited to copra harvests UNIQUE STOCKS WORLDWIDE species (Bour et al. 1986; Long et (eastern ) and agricul- al. 1993; Mumby et al. 1997; ture (Austral Islands). In some A 1994 synopsis of existing data Andréfouët et al. 2004). Maps and cases, giant clams can account for on giant clam stocks (all species numerical and weight estima- the equivalent of nearly 40% of combined) by Lucas (1994) tions have been made for giant copra income. showed that stock status varies clam stocks from Fangatau, significantly, depending on the Tatakoto and Tubuai (Gilbert et As is notably the case on Bora country. The general trend, how- al. submitted for publication) Bora and , the harvest- ever, is towards a decline in (Tab. 2), and similar work is cur- ing of giant clams to supply the stocks. Because of T. maxima’s size rently underway on Reao, Tahiti market runs the risk of and the way it attaches itself, it Pukarua, Fakahina and Raivavae. overexploitation, even in the rich- continues to be the least endan- est islands, and in spite of regula- gered species worldwide. Recorded densities in the tions governing the minimum Tuamotus were set at some 224 harvest size (a 1988 resolution set Quantitative and qualitative specimens/m2 in Reao Atoll in the minimum shell length at 12 inventories have occasionally the eastern Tuamotus (Salvat cm for fishing, transport, holding, been conducted in order to better 1967). Since that time, Andréfouet marketing and consumption). understand stock status and to et al. (2005) and Gilbert et al.

SPC Fisheries Newsletter #118 – July/September 2006 45 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA

(2005) have reported maximum (e.g. Papua New Guinea, Samoa, Tahiti and in French densities on Fangatau and Fiji, Australia) and in most Polynesia (Kim Friedman, pers. Tatakoto of some 136 speci- lagoons in French Polynesia, den- comm.). Comparative surveys of mens/m2 and 544 specimens/m2, sities are much lower, at most a the countries studied by respectively (Fig. 2). At present, few specimens per square meter, PROCFish, combined with the these two atolls have the highest and frequently, the figures are studies carried out by the SPE, densities of giant clams recorded given in hectares (Lucas 1994; will make it possible to determine anywhere in the world. These Green and Craig 1999; Skewes et where Polynesia fits, in terms of densities are linked to an al. 2003; Andréfouët et al. 2005). its nearshore resources, within the aggregative spatial structure (Fig. greater regional Pacific context. 2) specific to T. maxima in certain A survey by SPC's PROCFish semi-enclosed lagoons in the project, which covers most Pacific FRAGILE GIANT CLAM POPULATIONS eastern Tuamotus. These agglom- Island countries, is designed to erations sometimes lead to the obtain up-to-date information on Giant clam stock biomass and emergence of small biodetritic the status of invertebrate and fish structure in French Polynesia's islands made of shells, locally resources. The PROCFish team atolls, as studied by the SPE, can- called mapiko (Fig. 3). In contrast, has conducted surveys on the not be considered critical at this in many other areas of the world islands of Raivavave, , time but the situation could change rapidly. We cannot predict how these exceptional giant clam Table 2: Numerical and weight estimations of giant clam stocks populations grouped together in from Fangatau, Tatakoto and Tubuai the shallow parts of the lagoon will react to sustained exploita- tion. Giant clams' shallow water Total number of Total weight of giant clams Total weight saleable meat (L > distribution combined with their (millions) (tonnes) 12 cm) (tonnes sedentary behaviour and the fact they are easily found by fishers, Fangatau 23.6 ± 5.3 9 194 ± 2 158 1 162 ± 272 render them particularly vulnera- Tatakoto 88.3 ± 10.5 13 135 ± 1 573 1 485 ± 177 ble to fishing efforts. To this must Tubuai 47.5 ± 5.2 19 729 ± 2 109 2 173 ± 232 be added other specific traits linked to their biology and method of reproduction. Giant clams, which are known to have erratic recruitment, maximise their chances of reproduction by synchronised spawning (Munro and Gwyther 1981; Braley 1985). It would appear that there are

Figure 2 (top): Unusually high densities found in the reserve set up at Tatakoto (Photo Y. Chancerelle)

Figure 3 (bottom): Emerged area in Fangatau lagoon made of dead giant clam shells or Mapiko (Photo A. Gilbert)

46 SPC Fisheries Newsletter #118 – July/September 2006 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA chemical mediators or phero- when confronted with regula- becoming so unless the trade is mones in the and ovarian tis- tion violations and unsustain- regulated. International trade is sue (Wada 1954). The zones with able exploitation. permitted in Appendix II-listed the densest number of giant clams species, provided strict authorisa- are the areas where mass spawn- CITES AND INTERNATIONAL tion and monitoring systems are ing can be observed (Shelley and MANAGEMENT TOOLS in place. For that reason, export Southgate 1988), a phenomenon permits at departure and import we also observed in situ. In seden- When overexploitation has been permits at arrival are mandatory tary organisms, which spawn en noted in most regions, it has led for every commercial operation. masse, the total stock’s contribu- to measures designed to ensure tion to reproduction depends a the regeneration and protection Other regional initiatives have great deal on these zones of high of stocks. been undertaken. It is recom- density. But it is precisely in such mended that marine refuges or areas that fishing efforts are the At the international level, since restricted use areas be established highest. As soon as a high aggre- 1983, all giant clam species have in all areas where stocks are at gation area becomes depleted, been listed in Appendix II of the very low levels (Mitchell et al. there is, in addition to the changes Convention on the International 2001). It may take many decades in mean density, an underlying Trade in Endangered Species to replenish stocks if the part of effect on the population’s spatial (CITES), and are considered the reef involved is isolated or structure, which probably affects endangered species by the IUCN currents are not favourable pre-dispersion processes that (World Conservation Union). (Braley 1994; Munro et al. 1993; depend on density. Fishers then Appendix II means that the listed Lucas 1994; Mitchell et al. 2001; unwittingly target those speci- species is not threatened with Wells 1997). Reserves where fish- mens that have the best chance of extinction, but could be at risk of ing is prohibited have been set up reproducing, a recurrent phenom- enon that contributes to overhar- vesting in benthic fisheries (Orensanz et al. 2004).

In general, overexploitation is linked to a combination of fac- tors, including in French Poly- nesia:

• an increase in human popula- tion and fishing pressure;

• an increase in fishing effort, which is related to the avail- ability of more effective fish- ing equipment (boats and div- ing equipment);

• the development of storage, transport and intra/inter-island communication resources;

• the difficulties that regulatory authorities face, and even a lack of response of their part,

Figure 4 (top): Aerial photo of the enclosed eastern area of Tatakoto that has been declared a reserve (Photo A. Gilbert)

Figure 5 (bottom): Buoy marking the southern boundary of Tatakoto reserve (Photo F. Faana)

SPC Fisheries Newsletter #118 – July/September 2006 47 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA at Rose Atoll in American Samoa fertilisation and increase recruit- Stock dynamics have been stud- (Green and Craig 1999), Papua ment within and outside the zone ied in situ during tagging/recap- New Guinea (Kinch 2002), and (Lucas 1994). Finally, while giant ture experiments on Fangatau, Tatakoto in the Tuamotus (Figs. 4 clam farming is highly developed Tatakoto and Tubuai (Faben 1965; and 5) (Gilbert et al. 2005). in the Pacific (Bell 1999), speci- Pauly 1983; Pearson and Munro mens from hatcheries are rarely 1991). The initial results showed Setting a minimum size that cor- used for ecological purposes (e.g. wide variability, both within a sin- responds to sexual maturity is a repopulation) and are mainly des- gle lagoon and between islands frequently used measure that tined for the trade (e.g. (Gilbert 2005). allows giant clams to reproduce T. maxima is highly sought after at least once before they are har- for its colours), or the food mar- Studies have also been conducted vested. Initial maturity has been ket, in the case of larger species. on this fishery in order to gain an observed in the eastern Tuamotus overall view of the ecosystem. at between 5 and 6 cm (pers. A RESOURCE MANAGEMENT PLAN Exports were monitored on observ.). The minimum size for BACKED UP BY AN INNOVATIVE Tatakoto and Fangatau and are this species varies depending on SPAT PRODUCTION TECHNIQUE being estimated on Tubuai (Fig. the region: 18 cm on Guam and 6). In 2004, exports reached 16.4 Niue, 16 cm in Samoa, 15.5 cm in Stock surveys are a necessary but tonnes of marketable meat on Tonga, and 12 cm in French inadequate approach to imple- Tatakoto, and 5.5 tonnes on Polynesia (SPC 2005). menting sustainable exploitation Fangatau. On Tubuai, depending plans. Stock dynamics (i.e. on the survey, estimates reached Another approach consists of con- growth, natural mortality and between 8 and 30 tonnes centrating adult genitors so as to recruitment) are also very impor- (Lehartel 2003; Larrue 2005). The increase the probability of gamete tant (Beverton and Holt 1957). price depends on the distribution network used and varies between XPF 300 and 500/kg. Monitoring of fishers has shown that the catch per unit of effort (CPUE) in kg of marketable meat/man-hour) are between 2.7 kg/hour and 4.9 kg/hour (Fig. 7). Collec-tion site depths and differences in popula- tion structures (density and size) make it possible to explain these differences in CPUE between islands and even between sites on the same island.

These data were used to formu- late some initial recommenda- tions. Beverton and Holt’s model (1957) made it possible to analyse yield per recruit and, through that, biomass per recruit as a per- centage of biomass per recruit in an untouched state. Some inter- esting preliminary diagnostic information is available. However, the specific characteristics of invertebrate biology and fisheries make it difficult to apply the con-

Figure 6 (top): Monitoring giant clam exports from Tatakoto by weighing before maritime shipping (Photo A. Gilbert)

Figure 7 (bottom): Giant clam fishers-gathers in Fangatau lagoon (Photo A. Gilbert)

48 SPC Fisheries Newsletter #118 – July/September 2006 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA cepts and models used for finfish the past by the elders) and to seem to indicate that Tridacna fisheries management, and so monitor the integrated response maxima is predominant in the care should be taken with regards of the system (i.e. monitoring the pelagic larvae pool and, there- to the results from the Beverton spatial structure by means of a co- fore, has an excellent capture or and Holt model. Most inverte- management system). This group collection potential (local term brate species have strong spatial of measures should make it pos- from the oyster industry). structures, with adult stages that sible to apply the adaptive man- With a mean density of more than are only slightly, if at all, mobile agement needed for sustainable 400 specimens/m2 (Fig. 8) and a but with large-scale larval disper- exploitation of this resource. In collection rate of more than 80% sion. These characteristics con- the same way as what has been two years after the installation of tribute to a spatial structure of done with giant clams elsewhere the collectors, this method is very meta-populations, the dynamics in the Pacific, a co-management promising. This is the first suc- of which have only just begun to project for giant clam stocks and cessful use in the world of giant be modelled. Given that, work fisheries is being conducted in the clam collection techniques. This should continue and a precau- lagoons of Fangatau, Tatakoto spat collection method has a tionary principle should be and Tubuai. number of economic advantages applied to promote a homoge- over other Pacific producers nous distribution of the fishing At the same time, trials have been where a hatchery phase is effort (i.e. through a rotation carried out on giant clam collect- required (Tisdell and Tacconi 1992). strategy, or rahui zones used in ing, farming, transport and on The growth rate was also encour- the past by the elders), in order to restocking, using harvested giant aging with a mean size of more preserve source subpopulations clams. Low species richness and than 3 cm at the end of the first year (i.e. identify refuges for reproduc- the giant clam’s dominance in of farming. Using collected spat tion zones or tapu zones used in Fangatau and Tatakoto lagoons may, then, facilitate the develop- ment of giant clam resources.

The low level of genetic differ- ences between Tridacna maxima populations in French Polynesia (Planes et al. 2004) also makes it possible to plan transfers with no genetic risks. The low epibiont colonisation of young collected spat (7 cm or less), the existence of the same epibionts in the island groups where transfers are planned (Fauchille et al. 2004), and the possibility of conducting freshwater treatments before dry transfer, make it possible to limit the ecological risks during inter- island transfers. Inter-island transport trials involving an external freshwater treatment have been carried out using the Ellis method (2000), with a partic- ularly high survival rate of 95% after 10 hours of dry transport (Yan 2005).

Finally, in Tatakoto and Fangatau lagoons, reseeding trials (Fig. 9) that used more than 36,300 spat

Figure 8 (top): Giant clam spat collected (Photo L. Yan)

Figure 9 (bottom): Small island of restocked giant clams (Photo A. Gilbert)

SPC Fisheries Newsletter #118 – July/September 2006 49 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA

provided good prospects for today. This is certainly one of the ACKNOWLEDGEMENTS reseeding projects. Survival rates reasons for the success of an inno- in these two lagoons were 31% vative technique for spat collec- The programme has been funded and 71%, respectively, more than tion, an emerging sector of activi- by the Government of French 20 months after reseeding, and ty. But even in the case of these Polynesia (French Government- respective maximum rates dur- exceptional sites, the risk of over- Territory Development Contract, ing trials to improve the tech- exploitation cannot be ruled out Phase 2). Our thanks to the many niques were 57% and 91%. In over the medium- to long-term people and agencies who have addition, we noted that the new due to the current rate of meat participated in this project spat attached themselves to exports from the outer islands to include, in particular, Claude reseeded giant clams at a mean Tahiti and projected increases in Payri (IRD) for her significant con- rate for both lagoons of 8.3% and demand. Stock dynamics, and tribution to the work on stocks, 2.7%, and a maximum rate of fisheries and population dynam- Didier Gascuel (ENSAR) for his 55% and 15%, respectively. This ics studies were carried out on involvement in the management means that what is involved is three islands in French Polynesia and population dynamics work, not merely reseeding, but an in order to provide the initial Yannick Chancerelle (Centre de actual lagoon restocking method. information needed for sustain- Recherches Insulaires et However, this method must be able exploitation. These studies Observatoire de l'Environment – mastered in high island lagoons allowed preliminary use of the CRIOBE and l'Ecole Pratique des before the technology can be Beverton and Holt model but this Hautes Etudes – EPHE) for his transferred. model is based on certain participation in the field work on assumptions and does not take Fangatau, Tatakoto and his pho- Whether destined for ecological into account the importance of tography skills, and finally Pierre or fisheries (repopulation) proj- stocks’ spatial structures. So, Decoudras (UPF) for socioeco- ects, “ecotourism” (developing while taking a precautionary nomic and cultural work done to lagoons in front of hotels) or the approach and giving due consid- date and for work to still be car- aquarium fish trade, these giant eration to the giant clam’s specific ried out. Finally, we gratefully clam collection and reseeding biological traits, management acknowledge the welcome and methods offer an alternate way to must take into account this spatial support from the mayor’s offices, exploit and develop this resource, component. The methods pro- communities, and fishers in those and offers a new economic activi- posed seem to be relatively well- townships involved in this project. ty for isolated island groups in adapted to the local context as the eastern Tuamotus. However, they are similar to traditional REFERENCES modifying local regulations and management methods used in the CITES permits is the final step to past (e.g. the rahui strategy (rota- Addessi L. 2001. Giant clam be taken before this new source of tion), the tapu (total fishing prohi- bleaching in the lagoon of income can be fully developed. bition: reproduction refuges) and Takapoto Atoll (French The economic development tomite toohitu strategies (using Polynesia). Coral Reefs 19:220. potential of the collection sector is councils of elders to co-manage also a tool that supplements man- community property). However, Andréfouët S., Zubia M. and agement. Besides repopulation, it the only way to ensure that future Payri C. 2004. Mapping and can contribute to raising an entire recommendations are followed is biomass estimation of the community's awareness of the to have the involvement and sup- invasive brown richness and importance of this port of local communities. Scien- Turbinaria ornate (Turner) J. extraordinary resource, and can tific and technical efforts currently Agardh and Sargassum man- lead to sustainable exploitation. underway must be backed up by garevense (Grunow) Setchell meetings with island communi- on heterogeneous Tahitian CONCLUSION ties, listening to them, engaging in coral reefs using 4-meter reso- discussions, and attempting to lution IKONOS satellite data. The giant clam stocks of the pop- find mutually acceptable solu- Coral Reefs 23:26–38. ulated islands in the Society tions. The SPE should promote a group have clearly been over-har- changeover to multi-sectoral col- Andréfouët S., Gilbert A., Yan L., vested, but certain islands in the laboration, the only realistic way Remoissenet G., Payri C. and eastern Tuamotu and Austral to integrate and implement future Chancerelle Y. 2005. The Islands still have exceptional recommendations with a view to remarkable population size of giant clam concentrations. French involving all stakeholders in a the endangered clam Tridacna Polynesia has recorded giant clam joint project to sustainably co- maxima assessed in Fangatau stocks whose abundance, cover- manage stocks and fisheries. atoll (Eastern Tuamotu, age and densities are the highest French Polynesia) using in of any coral reefs in the world situ and remote sensing data.

50 SPC Fisheries Newsletter #118 – July/September 2006 SPECIAL TRAITS AND PROMISES OF THE GIANT CLAM (TRIDACNA MAXIMA) IN FRENCH POLYNESIA

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