Larval Fish Assemblages Differ Spatially and Temporally on a Large River

Little is known about larval fish communities in riverine systems. Since larval fish assemblages have been shown to vary on localized spatial and temporal scales, we were interested in comparing assemblages in a large river to identify environmental influences on assemblage structure. The Wabash River is the twelfth longest river in the contiguous United States and is the longest unimpounded river East of the Mississippi River. A major tributary of the Wabash River, the White River, effectively doubles the discharge of the Wabash at their confluence. Samples were collected by boat-mounted ichthyoplankton net for five minutes at eighteen sites along the lower 200 miles of the Wabash River. Catch per unit effort (number of fish per cubic meter, CPUE) was Log-transformed for all analysis. Preliminary results indicate the White River alters assemblage composition below its confluence throughout the year. The spatial and temporal differences in larval fish assemblages between the upper and lower reaches indicate fundamental differences in environmental characteristics are preferred for larval development below the confluence with the White River. During the spring and summer of 2016, we will be adding tributaries of the Wabash River for sample collection.