Abstract:
I studied spatio-temporal variation in fish assemblages on eight shallow gravel bars along a 34 kIn stretch of the Neosho River in Lyon County, Kansas, from November 2000 to October 2001. Analysis revealed temporal variation to be greater than spatial variation. Temporal variation was associated with fish life history events such as spawning and recruitment, and with abiotic environmental gradients. Spatial variation was related to the presence of two low-head dams that created contrasting lotic and lentic stream reaches with differing fish assemblages, similar to patterns predicted by the Serial Discontinuity Concept. Benthic and midwater guild fishes responded similarly to environmental gradients at the microhabitat level, although substrate played a slightly stronger role for the benthic fish assemblage. Juvenile members of both guilds generally utilized shallower, slower flowing habitat than adult conspecifics. Larger scale spatiotemporal patterns differed, however; the benthic guild showed significant spatial and temporal variation, whereas the midwater guild displayed neither. My results suggest that distinctions between water column habitat guilds may yield information helpful to understanding the structure and function of stream fish assemblages.
