Spatial synchrony and temporal dynamics of juvenile red drum Sciaenops ocellatus populations in South Carolina, USA

Across a species' range, the population dynamics of some areas may express spatial synchrony (i.e. they fluctuate with one another), whereas other areas may express no synchrony (they fluctuate independently). The degree of synchrony and spatial extent of synchrony are important considerations when assessing the population as a whole. We examined these aspects in red drum Sciaenops ocellatus along the coast of South Carolina using long-term survey data of juvenile abundance in estuarine areas separated by up to similar to 200 km. Synchrony of year class strength was detected among areas, but the degree of synchrony declined significantly with distance. By comparison, genetic segregation along the coast was either weak or undetectable (based on allele frequencies at 8 microsatellite loci), although it depended on the year class (2004, 2005 or 2007) of fish that was tested. By standardizing juvenile abundance data across estuaries and survey types, a single, region-wide juvenile time series was generated that covered the 1985-2007 year classes. The juvenile time series correlated significantly with the year class composition of the present-day adult population, which was determined using otoliths collected by a separate survey operating in deeper adult habitats. Future work integrating data across even broader spatial scales would assist in the understanding of large-scale ecological processes that control fluctuations in red drum populations, and would provide useful information for fishery managers.