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1 December 2010 Protracted Recruitment in the Bay Scallop Argopecten irradians in a West Florida Estuary
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Many studies have indicated that annual spawning of bay scallops (Argopecten irradians) peaks during discrete and limited periods each year. Spawning in most Florida bay scallop subpopulations has been shown to occur in fall, whereas more northerly U.S. populations typically spawn in late spring or summer. In this article we describe our efforts to expand our understanding of the seasonality of bay scallop recruitment dynamics in Florida. Visual surveys were conducted by divers each spring from 1994 to 2009 to estimate adult scallop abundance. Adult abundance was low (6.1 scallops/600 m2) during the first 3 y of the study (1994 to 1996), prompting a 7-y restoration effort intended to enhance the number of spawning adults and thereby enhance the local production of larval scallops. Adult abundances increased to an average of 21.9 scallops/600 m2 in 1997 to 2006, and then rose dramatically to an average density of 154.8 scallops/600 m2 in the most recent years (2007 to 2009). Artificial recruit collectors (n = 12) were deployed monthly near the Anclote River estuary beginning in 1997 and were allowed to soak for 2 mo at a time. Each collector's deployment period overlapped with the preceding and following trap's deployment period by 1 mo. The project is ongoing, but only data collected through December 2009 is included here (bay scallops recruited to the collectors during 163 of the 185 deployment periods). For the entire study period, the average recruitment rate was 0.3 scallops/collector/day, the maximum average for a single deployment period was 5.5 scallops/collector/day during November 2001 to January 2002, and the highest rate for a single collector was 19.6 scallops/collector/day during November 2001 to January 2002. In most years, the collectors retrieved in late fall and early winter had the highest settlement rate; a secondary recruitment peak was observed in the spring. A period of protracted recruitment (December 2005 to December 2009) occurred, during which scallops recruited to at least 1 of the 12 deployed collectors deployed during 53 consecutive deployment periods. The average recruitment rate for this protracted period was 0.4 scallops/collector/day; the maximum recruitment rate for a single deployment period (3.5 scallops/collector/day) and individual collector (17.7 scallops/day) occurred during December 2008 to February 2009. Early in our study, scallops were detected in a majority of our recruit collectors, and a protracted period of recruitment (October 2001 to February 2004) coincided with the multiyear restoration effort. However, the recent high adult densities and protracted period of recruitment occurred in the absence of any active restoration in this subpopulation, suggesting that, at least within the Anclote River estuary, the population has stabilized for the short term.
Stephen P. Geiger, Sarah P. Stephenson and William S. Arnold "Protracted Recruitment in the Bay Scallop Argopecten irradians in a West Florida Estuary," Journal of Shellfish Research 29(4), (1 December 2010).

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