INCREASE IN BAY SCALLOP (ARGOPECTEN IRRADIANS) POPULATIONS FOLLOWING RELEASES OF COMPETENT LARVAE IN TWO WEST FLORIDA ESTUARIES

We propose the release of ready-to-set pediveliger larvae as a restoration strategy for bivalve shellfish. In this study, bay scallop (Argopecten irradians) larvae were released within two West Florida estuaries (Pine Island Sound and Boca Ciega Bay) currently closed to scallop harvest and where local scallop populations are severely depleted relative to historical abundances. Populations in both estuaries appear to have limited larval supply and show no tendency toward natural recovery after decades of decline. Larvae were either released into enclosures or free released on four separate dates in each estuary. On a given day we used 1, 2, 3, or 4 enclosures per site; multiple release sites; and multiple releases within a year. Assessments were made via several methods, including larval recruitment to collectors, juvenile quadrat surveys, adult timed surveys, and adult transect surveys. In Pine Island Sound, following the initial larval releases in 2003, an isolated recovery in adult scallops was observed at the release site in 2004 followed by a massive resurgence in the local population in 2005. This population declined dramatically in 2006, however, and had completely collapsed by 2007. In Boca Ciega Bay, the series of larval releases did not immediately produce any detectable scallop patches, but the combined releases did immediately precede a population resurgence to levels greater than had been observed in the past three decades. Scallop abundance increased 10-fold at 10 stations in Boca Ciega Bay from 2007 to 2008. In both Pine Island Sound and Boca Ciega Bay, the increases in scallop populations were probably the result of successful survival, growth, and reproduction of the released larvae, followed by successful recruitment and growth of the subsequent generation.