Restoration of bay scallop (Argopecten irradians (Lamarck)) populations in Florida coastal waters: Planting techniques and the growth, mortality and reproductive development of planted scallops

Bay scallops (Argopecren irradians [Lamarck]) are a culturally and economically important component of Florida's nearshore marine community. However. many of the local populations that compose the bay scallop metapopulation in Florida have virtually disappeared since the 1950s. This study reports the results of a 3-year effort to restore bay scallop populations at 4 sites along the west central coast of the state (Tampa Bay, Anclote, Homosassa and Crystal River). During late summer of 1997, 1998 and 1999, wild adult scallops were retrieved from each of those four target sites and induced to spawn in the laboratory. The resultant offspring were grown to at least 20-mm shell height in a nursery setting and then transplanted to cages deployed at the site where their parents were originally harvested. The growth. survival and reproductive development of the planted scallops were recorded on an approximate 6-week schedule. Results suggest that caged scallops generally grew more slowly than their wild counterparts and that at most of the planting sites mortality was high, especially during late summer. Reproductive development and spawning, although delayed in the caged scallops relative to their wild conspecifics, appears to have proceeded in an otherwise normal fashion. Approximately 1,100 scallops survived and spawned during the first year of the project, whereas similar to 4,700 and 12,000 scallops survived to spawn in the second and third years of the project, respectively. Studies were also conducted to determine the optimal stocking density and the best placement of the cages. Results of the density study indicate that planting at lower densities increased growth and survival but did not necessarily result in more live scallops at the time of spawning. Results of the cage-placement study, which compared scallops planted in cages either inside or outside of a seagrass bed and either mounted on legs or placed directly on the sediment, revealed that scallops planted directly on the substrate within a seagrass bed suffered higher mortality and slower growth than did scallops planted in the other three treatment combinations. Overall results of this 3-year project suggest that planting cultured scallops in cages can be a successful strategy for increasing the local spawner stock density of bay scallops in depleted populations and, ultimately, for increasing larval supply to the metapopulation.