The giant clam Tridacna maxima communities of three French Polynesia islands: comparison of their population sizes and structures at early stages of their exploitation

Abstract

Several lagoons of the atolls of Tuamotu Archipelago and volcanic islands of the Australes Archipelago (French Polynesia) are characterized by enormous populations of the clam Tridacna maxima, a species considered as endangered in many locations worldwide. Even if this resource can still be considered as virtually intact, the growing harvesting pressure to feed Tahiti's market (up to 50 t of wet matter y−1), combined with the relatively small size of these lagoons, will soon call for management action to sustain a fishery that currently targets a large, virtually pristine stock. Hence, we present T. maxima population sizes and structures for two atolls (Fangatau and Tatakoto) and one island (Tubuai), where high clam densities and population sizes have promoted a small-scale, but growing, commercial fishery since the late 1990s. We followed an earlier pilot study, in which a combination of remote sensing and in situ data provided an estimate of the Fangatau clam population size (23.6 ± 5.3 million clams, mean ± 95% confidence interval, for 4.05 km2 of mapped lagoon). We obtain 88.3 ± 10.5 and 47.5 ± 5.2 million clams for Tatakoto (mapped area of 11.46 km2) and Tubuai (mapped area of 16.3 km2), respectively. Accounting for contrasted length frequency distribution curves and one common size–weight relationship, the total biomasses are 1485 ± 177 t, 1162 ± 272 t, and 2173 ± 232 t of commercial flesh for Tatakoto, Fangatau, and Tubuai, respectively. In addition, given the legal restriction on collecting clams smaller than 12 cm, the legally harvestable biomasses are 958 ± 114 t, 1038 ± 247 t, and 1971 ± 210 t of flesh for Tatakoto, Fangatau, and Tubuai, respectively. The ratio between legal and total stock is much smaller for Tatakoto because this atoll is dominated by small clams, unlike the other two sites. The differences in population size and structure are discussed in terms of natural environment (habitats, degree of aperture to the ocean, temperature variations), providing insights on the natural variability between two similar systems (Tatakoto and Fangatau), and between different systems (the two atolls and the volcanic island of Tubuai), suggesting that future management schemes will have to be optimized locally.

Diversity and abundance of giant clams in Anambas Islands, Indonesia

“…This is very different from the results obtained in Ashmore, Mermaid and Cartier Reefs, located within the Great Barrier Reef, host populations in excess of 100 indv.m -2 . Another example is on Tatakoto, French Polynesia, has an abundance of 90.9 indv.m -2 [19,20]. The results of the data analysis show that the RA of giant clam ranged between 2.36% to 60.54%.…”

Dominant benthic mollusks in closed atolls, French Polynesia

“…On Reao (Salvat 1971(Salvat , 1972, we noted the maximum density up to 224 T. max ima and 42 P. maculata per m 2 with a total abundance in the border of the lagoon (0-6 m depth 3.7 km 2 on 39 km 2 for the whole lagoon) of 11.5 million mollusks each. On Tatakoto 544 T. maxima per m 2 have been reported as the maximum density (Gilbert et al 2006). Those densities are the most significant in the world (Salvat 1971;Gilbert et al 2006).…”

“…On Tatakoto 544 T. maxima per m 2 have been reported as the maximum density (Gilbert et al 2006). Those densities are the most significant in the world (Salvat 1971;Gilbert et al 2006). Whereas on Takapoto lagoon (77 km 2 ) 93 mollusks have been identified in the lagoon, 4 of them (P.…”

Captive Bred, Adult Giant Clams Survive Restoration in the Wild in Seychelles, Indian Ocean

“…With their large size and stunning colors ranging from electric blue, green, pink, and purple to gold, giant clams are equivalents of "charismatic megafauna" that can act as flagship taxa, drawing attention to the ongoing destruction of coral reefs (Soo and Todd, 2014). Giant clams have ecological significance as reef builders, contributing to the calcium carbonate framework of coral reefs (Barker et al, 1988;Gilbert et al, 2006), as food for 75 known predators and a scavenger guild, shelter for juvenile and adult coral reef fish, shell surfaces for epibionts and as hosts for ectoparasites and commensals (Neo et al, 2015). Giant clams are simultaneous hermaphrodites that spawn sperm first and then eggs during a spawning event (Wada, 1952).…”