Re-introduction of giant clams in the Indo-Pacific

Summary

Giant clams (family Tridacnidae), the Indo-Pacific's largest marine bivalves, have been depleted across much of their range by subsistence and commercial fishing for meat, shells, and the aquarium trade, with several species locally extinct at sites including Guam, the Federated States of Micronesia, New Caledonia, and Fiji. Since the early 1980s, a coalition including the Okinawa Prefectural Fisheries Experimental Station, the University of Papua New Guinea, and the WorldFish Center pursued two complementary restoration approaches: aggregating scattered wild adults into clam circles to overcome the low-density fertilization failure known as the Allee effect, and hatchery breeding for restocking, now practiced in over 21 Indo-Pacific countries. At Tonga's Falevai clam circle, juvenile Tridacna derasa detection rose from zero in 1987 to 1.48 individuals per search-hour by 1990, with T. squamosa showing an even larger increase. Hatchery-based restocking achieved mixed results: in the Philippines, of 10,000 T. gigas clams placed in Hundred Islands National Park, 7,531 survived after 2.5 years, mostly losing only juveniles to typhoons, fouling, and poaching, while in Yap, 25,000 translocated T. derasa from Palau saw only about 8 percent survival yet still established a reproducing population documented into 2006. Survival of restocked T. crocea in Japan ranged from 0.3 to 56 percent depending on substrate placement method. The project rated itself Partially Successful, citing strong hatchery technology adoption offset by high juvenile mortality, funding limitations, inconsistent monitoring protocols, and social mismatches with some participating communities.