Spat collection of giant clams Tridacna maxima : first results and promises from Eastern Tuamotu lagoons G. Remoissenet (a), L. Yan(b), A. Gilbert(c) and S. Andréfouët (d) (a) Service de la Pêche, BP 20 Papeete 98713 , Tahiti, French Polynesia [email protected] (b) Aquaculture consultant, BP 1658, Papeete 98713 , Tahiti, French Polynesia (c) Reef Fishery scientist, BP 140211 Papeete 98701 , Tahiti, French Polynesia (d) Institut de Recherche pour le Développement, BP A5, 98848 Nouméa, Nouvelle Calédonie French Polynesia Fisheries agency « service de la pêche » has developed a program based on management, exploitation and restocking of giant clams, Tridacna maxima. I In order to set up a rational exploitation scheme of this resource and sustainable incomes for targeted islanders, fisheries and aquaculture research has been investigated. An original and suited model of development has been designed and implemented for this species : spat collection techniques, transport, rearing and restocking techniques have been designed and mastered in Tatakoto and Fangatau lagoons, with a view to get sustainable exploitation of giant clams on different markets GIANT CLAM IN FRENCH POLYNESIA The international trade market of giant clams is regulated by the CITES (International Worldwide highest densities Convention on the Trade of Endangered species). World Ornamental market for giant clams is : ü average 200 000 clams per year, from which 50% only for Tridacna maxima In French Polynesia, Tridacna maxima , the most represented species, is: ü Regulated by a resolution setting 12 cm as the size limit of the shell for fishing, transport, holding, Chancerelle 2004. Chancerelle marketing and consumption, 2004. Chancerelle ü Overexploited in some islands, but well-represented in a few lagoons of Eastern Tuamotus and Australes archipelagos ü Consumed on Tahitian local market at a level of around 70 tonnes of flesh, that is about 300 000 Remarkable clustered structures (locally called « mapiko ») and individuals every year. natural densities up to 500 clams per m² in Tatakoto FANGATAU ET TATAKOTO : TWO ATOLLS PILOT FROM EASTERN TUAMOTUS Caractéristiques générales de Fangatau et Tatakoto • 250 inhabitants • 19,62 km² lagoon • Reef aperture rate of 12,1% ü North-East Tuamotu (Fig. 1) Mosaïque de 3 photos aériennes de Mosaïque 3 photos • Exploitation stock (> 12 cm) of 307 +/- 69 tons of flesh ü Small size atolls, shallow lagoon without any pass Fangatau • Around 20 tons of flesh exported to Tahiti Andrefouët 2004. Andrefouët • 150 inhabitants every year since 10 years ü Lagoons with exceptional richness of giant clams • 9.9 km² lagoon • Reef aperture rate of 6.4% ü Local economy based on copra and recent exploitation of • Exploitable stock (> 12 cm) of giant clam flesh on tahitian market 364 +/- 85 tons of flesh Figure 1: Fangatau and Tatakoto location • Around 4 tons of flesh exported to Tahiti DigitalGlobe©. Quickbird every year since 10 years Tatakoto GIANT CLAMS COLLECTION, CULTURE, TRANSPORT AND RESTOCKING STUDY Giant clam spat collecting method Spat collection : some results Transport method between islands A specific approach : classic spat collection methods (for pearl oysters, Spat shell length structure observed on collectors is related ü Dry transport with preliminary freshwater bath to oysters and mussels) have been fitted to giant clams with the wild populations clam shell length structure (Fig.2&3) eliminate major epibionts Ø Aged stock and spat collecting frequency low in Fangatau ü Gel pack addition in freight box to low Ø Low depth submerged rafts (<2m) placed in the most lighted zone Ø Young and well productive stock in Tatakoto : spat collecting temperature and therefore slow down metabolism (for the zooxanthellae of giant clams mantle) is more frequent (reef aperture rate is two times higher thus ü Maximum transport duration should be less than Ø Artificial shade cloth is laid down horizontally (face to sunlight) increasing ocean-lagoon exchanges, therefore spawning). 12 hours for a 95% minimum survival rate. and hold tight (as T.maxima is usually anchored to hard substrate) 12% 10% FANGATAU TATAKOTO FANGATAU TATAKOTO Restocking results 8% L moy= L moy= 10,3 +/- 4,4 cm 7,2 +/-4,3 cm 6% ü Total restocking of 36 355 collected giant clams, 4% sizes ranging from 5 to 9 cm 2% ü Best result is obtained on clustered shells 0% habitat, with a global rate of 57,7% of clams 10 30 50 70 90 110 130 150 170 190 210 230 Yan 2003. mm alived settled 54 months after restocking Figure 2 : Wild giant clams size structure in Fangatau and Tatakoto ü New setllement of 20 to 30% of new spats is 10% FréquenceFANGATAU FL observed on giant clams reseeded on clustered 8% habitat 6% FréquenceTATAKOTO TL Number Survival rate 4% 3500 100% Lay down of a collection device for giant clams 2% 3000 0% 80% 2500 mm 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 mm 2000 60% Figure 3 : Spat collecting profile one year after laying the devices 1500 40% % ind/m² 100 600 1000 500 20% 500 75 Rate of Yan 2003. 400 Success on 30 devices 0 0% 50 300 March 2004 J 0 J 115 J 401 J 470 J 598 J 814 J1163 J1628 Medium 200 density on gravel coral pavement shells New spat 25 collector 100 Gravel Pavement S hells 0 0 Figure 5 : Restocking type influence on survival of giant 1 2 3 years after laying clams obtained after 4.5 years. Collected spats on collector Figure 4 : Spat collection rate and density of giant clams spats DEVELOPMENT OF GIANT CLAM AQUACULTURE BASED ON SPAT COLLECTION : PERSPECTIVES Spat collection giant clams : which markets from short to long term duration ? Regulations suited to sustain development from remote islands ü Objective of new aquaculture regulation ü On a short term period : niche market of marine ornamentals - spat collection development in suited sites for a quality product and an eco-friendly image - sustainable exploitation of the resource - collecting, rearing and restocking livestock traceability Yan 2006. ü On a short term period : local eco tourism market ü Main objectives of the future regulation on exportation : for submarine gardens and for an exceptional image of the country - banned wild adult stocks capture, (no traceability, nor warranty for the quality of the product) ü On a mid-term period : international live giant clams flesh Restocking on clustered - promote sustainable development of a spat collection and Market to be estimated (Japan, China, etc…) type habitat : « mapiko » culture based industry from remote islands reconstructed ü On a long term period : local flesh market Yan 2006. ü This specific giant clam industry based on sustainable aquaculture and its unique Based on restocking of collected spats characteristics must now become a succes story. Last but not least, it may help as a Model to be specified and planned out with islanders strong marketing key for eco tourism image in French Polynesia. Andréfouët S., Gilbert A., Yan L., Remoissenet G., Payri C., Chancerelle Y. (2005) The remarkable population size of the endangered clam Tridacna maxima assessed in Fangatau atoll (Eastern Tuamotu, French Polynesia) using in situ and remote sensing data. ICES Journal of Marine Science. Vol. 62, Issue 6, pp 1037-1048. Ellis S. (2000) Nursery and Growt-out Techniques for Giant Clams (Bivalvia: Tridacnidae). CTSA Publication N° 143: 99 p. Gilbert A., Andréfouët S., Yan L., Remoissenet G. (2006) The giant clam Tridacna maxima communities of three French Polynesia islands: comparison of their population sizes and structures at early stages of their exploitation, ICES Journal of Marine Science .63 : 1573-1589. Lucas J.S. (1994) The biology, exploitation, and mariculture of giant clam (Tridacnidae).Rev.Fish.Sc. 2 (3).P 181-223. Teitelbaum A., Friedman K. J. (2008) Resurgence of cultured giant clams from the pacific; current status and prospects for the aquarium market Australasian Aquaculture conference, Brisbane Australia. Plenary talk.