Diel variation in habitat use by stream fish

Edward E. Leonard and William E. Ensign
Department of Biological and Physical Sciences, Kennesaw State University Kennesaw, GA 30144; 770-499-3505 (phone); 770-423-6625 (fax); bensign@kennesaw.edu

We investigated variation in microhabitat selection by stream fish between day and night hours. We sampled a small warm-water stream using a point observation technique. Observations were made using mask and snorkel. The stream was divided into habitat units and five points were selected within each unit. Transects were laid at five random points in each habitat unit, and one sampling point was chosen at random along the length of each transect. Depth, mean water velocity, and substrate composition were measured at each of the observation points. A single observer counted all fish present within one meter of the point selected. Samples were taken in daylight and at night with diurnal and nocturnal runs within 24 hours of each other. Night samples were taken using a submersible flashlight. Samples were taken in spring and fall, 1999. Preliminary results from spring indicate selection of shallow water at night and deeper water during the day in most species. This pattern seems to become weaker during the fall. Some fish show no selection during fall while others reverse selection as compared to spring. Variation in light intensity appears to cause shifts in microhabitat requirements among stream fishes. Assessment of species-specific microhabitat requirements may be directly dependant on when assessments are made.