The Microhabitat Distribution of the Arkansas River Shiner, Notropis girardi: A Habitat-mosaic Approach

Abstract

I evaluated the microhabitat distribution of the Arkansas River shiner, Notropis girardi, a candidate species for protection under the Endangered Species Act over a two-year period. Seasonal microhabitat samples were taken at three localities along the South Canadian River in central Oklahoma. The microhabitats sampled were defined subjectively based on structural and substrate characteristics: adjacent to stream banks, underwater sand ridges, or exposed sand islands, and within stream pools, midchannels, or backwaters. At each microhabitat, the following physicochemical measurements were made: depth, temperature, current speed, dissolved oxygen, conductivity, and pH. Notropis girardi used many microhabitats and the patterns varied seasonally and ontogenetically. Contingency tests indicated that bank, island, and sandridge habitats had significantly more N. girardi than the others (p<0.01), whereas midchannel habitats were used significantly less often than other habitat types. A greater number of individuals were found in microhabitats defined by depths of 0–50 cm and current speeds of 0–50 cm s^-1 although faster current speeds were used with high frequency. Selection of deeper water was only apparent during the summer. Juveniles selected shallow, slow flowing backwater habitat types more frequently than did adults. Habitats adjacent to underwater sand ridges were important to both adults and juveniles, but similar types such as islands and banks also were used. No single physicochemical feature was linked to high densities of this species. During its life cycle, N. girardi used most of the range of features encountered in the S. Canadian River; thus, maintenance of the riverine landscape (i.e. all of the attributes of rivers in the native range of N. girardi) will be necessary to ensure that this species has access to appropriate habitat types throughout its life cycle.