A GIS approach for explanation of fish assemblage structure in a large river

Abstract

Although using Geographic Information Systems (GIS) has become common in ecology, few river stud- ies incorporate this technology into examining habitat variables and use of habitat by individual fishes. Our goal was to demonstrate these GIS techniques and to test for the ability to predict fish and habitat relationships using the same data in a multivariate analysis. We collected channel bathymetry, water velocity, and streambed composition using an Acoustic Doppler Current Profiler (ADCP) deployed from a USGS boat and interfaced with a Differential Global Positioning System (DGPS) receiver, for a 10-km study reach of the Wabash River. Individual fishes were collected the following week and assigned spatial coordinates for latitude and longitude. We tested for the ability of a multi- variate technique to explain fish assemblage variation using environmental variables collected in a GIS context. We tested at which of three resolutions the environmental variables explained the highest proportion of fish assemblage variation. For this 10-km reach of the Wabash River, fish assemblages were best explained at a 10 by 10 m resolution with water velocity, water depth, river location, woody debris, and substrate composition. At a lower resolution (30 by 30 m) the same habitat variables provided similar but lower explanation of variation. However, at the highest resolution of 4 by 4 m, environmental variables provided relatively little explanation of fish assemblage structure. We suggest and recommend additional applications of a GIS approach to test temporal and spatial hypotheses of stream fish assemblage structure.