Application of larval release for restocking and stock enhancement of coastal marine bivalve populations

The coastal zone in the United States and in other areas worldwide is under increasing stress from human population growth and associated development, and that stress extends to the animal populations that occupy coastal habitats. Considerable effort is being expended to restore the habitats and animals that characterize this biome. I herein describe historic and recent developments regarding the application of the larval release approach to marine animal population restocking efforts. Beginning with cod (Gadus morhua) larvae in the late 1800s, the larval form has been exploited for restocking of various fish and invertebrate species with mixed results. Success has been elusive when working with cod and hard clams (Mercenaria spp.), but efforts using striped bass (Morone saxatilis), abalone (Haliotis spp.), and most recently bay scallops (Argopecten irradians) have been at least partially successful. In the case of bay scallops, competent (ready-to-settle) larvae released into containment enclosures were tracked through the post-settlement, juvenile, and adult life stages. That sampling scheme provided evidence that the released larvae ultimately contributed to a substantial increase in the subsequent year-class. However, those results are equivocal, and rigorous genetic sampling will be required to fully document the linkage between larval release and subsequent year-class strength. It is concluded that larval release, while not suitable for all species in all situations, may be an effective strategy for rebuilding marine animal populations.