Regional population structure and management of aquaculture for stock enhancement of the spotted seatrout (Cynoscion nebulosus)

• Spotted seatrout is cultured for stock enhancement in Mississippi.
• Knowledge of population structure is needed to monitor and manage genetic effects of stocking.
• 15 microsatellites were surveyed in Mississippi bay systems and neighboring populations.
• Mississippi populations were homogeneous but an isolation-by-distance pattern was evidenced.
• Management of stocking in Mississippi using a single broodstock is discussed and will require additional information on population density and gene flow.

The spotted seatrout, Cynoscion nebulosus is one of the most popular game fish in coastal waters of the north central Gulf of Mexico. An aquaculture-based stock enhancement program that aims to supplement native wild populations in Mississippi was initiated in 2004 as part of management efforts to sustain stocks and provide additional fishing opportunities to anglers. A genetic program associated with stock enhancement is in development and seeks to assess the effects of stocking on genetic diversity and fitness of wild populations, and design and implement genetic management to monitor and minimize those impacts. In this work, the structure of spotted seatrout populations in the region was investigated in order to assist with the development of a sustainable spatial management of stocking operations. Spotted seatrout specimens were collected during 2010 and 2011 from the four major bay systems in Mississippi and from reference populations in Louisiana (Grand Isle), and West Florida (Pensacola and Apalachicola). Sample size per locality ranged from 53 to 105 specimens. All samples were assayed at 15 microsatellite markers. Divergence among bay systems from Grand Isle (Louisiana) to Grand Bay (Mississippi–Alabama border) was low and non-significant. However, significant divergence between these localities and the Apalachicola location (West Florida) was detected (0.0214 < FST < 0.0264, P < 0.001), consistent with an isolation-by-distance model of population structure. Estimates of local effective population size by the linkage disequilibrium method were very large or infinite in most localities within the Western part of the sampled range (Mississippi and Louisiana) suggesting current population density is high in that region. While the lack of divergence among Mississippi bay systems supports genetic management as a single unit, further work is needed to determine the spatial scale of natural dispersal and assess the degree of local adaptation of regional populations.