GROWTH AND MORTALITY OF TRANSPLANTED JUVENILE HARD CLAMS, MERCENARIA-MERCENARIA, IN THE NORTHERN INDIAN RIVER LAGOON, FLORIDA

Growth and mortality were examined in hatchery-produced, early-juvenil e Mercenaria mercenaria transplanted to protected and unprotected plot s at a site in the northern Indian River lagoon, FL. Clam density and size were examined in both treatments five times in the year after tra nsplantation. The growth of clams in both treatments was rapid and com parable to that of clams from other areas within the lagoon. Growth in the protected treatment was initially depressed, but after 363 days, clams from both treatments did not differ significantly in shell heigh t (SH). The mortality of clams in both treatments was high, although s ignificantly greater in the open treatment. Clams in the protected tre atment died at a high rate until 80 days into the experiment (SH about 8 mm), beyond which no significant mortality occurred. This experimen t suggests that (1) growth rates in the northern Indian River lagoon m ay favor future aquaculture ventures; (2) clams can be grown out in th e lagoon (if protected from epibenthic predators) when they are 8 mm S H, much smaller than current aquaculture practice suggests; and (3) pl acing unprotected juvenile clams in situ at high densities is not an e fficient stock-enhancement technique.