Productivity of Functional Guilds of Fishes in Managed Wetlands in Coastal South Carolina

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Naturally-functioning estuarine intertidal wetlands are net exporters of secondary production, but impounded wetlands that are not subject to regular tidal inundation do not allow for the export of secondary production.  In coastal South Carolina, many 18^th-century ricefield impoundments currently are managed as migratory waterfowl habitat.  Water-level manipulation in these impoundments closes intertidal habitat to fish migration for most of the year; and when open, only limited migration occurs.  The effects of impoundments on fish production and energy transfer are largely unknown.  We used the size‑frequency method to estimate summer production of fish estuarine-use functional guilds in three Combahee River impoundments.  The guilds included amphidromous (AM), catadromous (CA), and estuarine species (ES), freshwater migrants (FM), freshwater stragglers (FS), and marine migrants (MM).  We predicted that production would vary depending on impoundment characteristics such as salinity.  Big Rice Field (BRF) is most the saline (17 – 21 psu) of the three impoundments, Nieuport is intermediate (4 – 16 psu), and ACE is freshest (3 – 9 psu).  We expected MM production to be highest in BRF, where salinity is similar to natural habitat.  We also expected that FM and FS production would be highest in ACE.  MM production was highest in BRF in 2008 (23.30 g·m^-2·summer^-1) and 2009 (20.92 g·m^-2·summer^-1), but highest in Nieuport in 2010 (30.22 g·m^-2·summer^-1).  FS production was highest in ACE throughout the study (15.56 – 117.38 g·m^-2·summer^-1).  FM production was highest in ACE in 2008 (16.64 g·m^-2·summer^-1), but highest in Nieuport in 2009 (7.03 g·m^-2·summer^-1) and 2010 (5.02 g·m^-2·summer^-1).  Our values provide estimates of fish biomass retained in impoundments.  Production of other guilds was low for all years, which indicates that impoundments may provide poor habitat for these guilds.