Relative Abundance, Growth, and Mortality of Five Age‐0 Estuarine Fishes in Relation to Discharge of the Suwannee River, Florida

Abstract

AbstractUnderstanding the relationships between river discharge and recruitment of estuarine fishes is important because of hydrological alterations caused by anthropogenic water withdrawals. Varying river discharge alters salinity, turbidity, nutrient levels, and detrital concentrations, all of which affect estuarine biota. The lower Suwannee River, Florida, is one of the few remaining large‐river systems in the United States that has no major impoundments. We assessed the relationship between seasonal river discharge and relative abundance, growth, and mortality of estuary‐dependent age‐0 fish of five species in the Suwannee River estuary. We analyzed 9 years of data (1997–2005) collected as part of a long‐term, fishery‐independent monitoring program. The results showed a positive relationship between relative abundance and river discharge for age‐0 spotted seatrout Cynoscion nebulosus, sand seatrout C. arenarius, and red drum Sciaenops ocellatus. The pinfish Lagodon rhomboides was the only species for which relative abundance was negatively related to river discharge; the relative abundance of spot Leiostomus xanthurus was not significantly related to changes in discharge. Instantaneous daily growth (G) estimates were positively related to river discharge for all species except spotted seatrout, for which a negative correlation was found. Instantaneous daily mortality (Z) estimates were positively correlated with river discharge for sand seatrout, pinfish, and red drum. The G: Z ratios for pinfish and early recruiting sand seatrout were negatively related to river discharge, indicating that recruitment potential declined with higher discharge. Changes in freshwater discharge affected the abundance, growth, and survival of these juvenile fishes, stressing the importance of water allocation decisions that affect estuarine fishes and the fisheries they support.