Growth and survival of hatchery-bred giant clams (Tridacna gigas) in an ocean nursery in Sagay Marine Reserve, Philippines

Abstract

To restore the diminishing population of the giant clam Tridacna gigas in Sagay Marine Reserve (SMR), Negros Occidental, central Philippines, two size classes [8-and 10-cm shell length (SL)] of hatchery-bred T. gigas were reared in an adjacent ocean nursery for restocking to Carbin Reef later upon reaching grow-out size of C20 cm SL. Growth rates did not significantly differ for both sizes and were on average 0.67 cm month -1 . However, survival after 382 days of rearing T. gigas was significantly higher in the 10-cm SL clams than the 8-cm SL clams (96 and 83%, respectively). For future restocking projects, the use of 8-cm SL clams is recommended because the lower survival of this size class is compensated by its cheaper price. While rearing the clams to attain grow-out size, the population of wild clams (Family Tridacnidae) in Carbin Reef was assessed using ten 50 9 2-m belt transects. Four species of tridacnid clams have been recorded: Hippopus hippopus, Tridacna crocea, T. maxima, and T. squamosa. T. crocea comprised 12.5-93.9% of all the clams observed in all ten transects. There was a significant difference in clam density between species (ANOVA, F = 6.94, P \ 0.001), with T. crocea having the highest density. Living T. gigas were absent, but presence of dead shells was indicative of its presence in the reef in the past. It can be expected that the release of hatchery-bred T. gigas juveniles in Carbin Reef could provide future breeders that will repopulate this reef and the adjacent reef communities.

Advances in Breeding and Rearing Marine Ornamentals

“…Recent studies addressing the role that incrusting coralline algae may play in the settlement of larval Tridacna revealed that it may attract larvae but does not promote settlement in Tridacna squamosa (Neo et al 2009). Another study by Lebata‐Ramos et al (2010) confirmed the potential of using giant clams produced in captivity for grow‐out in ocean nurseries. However, this approach is unlikely to ever be implemented in European waters (or other places outside the natural distribution of giant clams) to supply the marine aquarium trade.…”

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“…While there is no published information on the long term growth of restocked giant clams in the Philippines (Lebata-Ramos et al 2010), the use of von Bertalanffy growth formula is the simplest possible way to estimate the ages of live T. gigas and its empty shell. The use of other methods such as growth increment is impossible as most of the samples were only solicited and obtained from the KIs.…”

“…In the Philippines, giant clams are harvested for both meats and shells (Gomez and Mingoa-Licuanan 2006;Lebata-Ramos et al 2010;Miguelmies and Sumida 2012;Wabnitz et al 2003), but the shells have the greatest economic importance (Juinio et al 1987) especially for international trade (Lucas 1994). The Bureau of Fisheries and Aquatic Resources reported an export of about 243 to 11,930 tons of giant FULL PAPER clams between 1976clams between and 1980clams between (BFAR 1980; however, the volume of trade sharply declined at about 39 to 66 tons due to unregulated harvest (Wells 1997).…”

Evaluation of Post-Release Behavior, Recapture, and Growth Rates of Hatchery-Reared AbaloneHaliotis asininaReleased in Sagay Marine Reserve, Philippines

“…The reef flat, approx. 20 ha, is exposed during low tide when the water level goes beyond 0.3 m depth above chart datum (Lebata-Ramos et al, 2010).…”