Fish use of ecohydraulic-based mesohabitat units in a low-gradient Illinois stream: implications for stream restoration

1. A classification scheme for ecohydraulic-based mesohabitat units was developed for a summer low-flow period, Mesohabitat unit designations were based oil the integration of three-dimensional channel hydraulics. geomorphic maintenance processes of bed morphology. and biological resource needs of fish. Ecological relevance Of the units was evaluated by a study of fish mesohabitat use patterns. and species relationships to feeding guild. By portraying the stream as a mosaic of hydraulic habitat patches that provide specific biotic resource needs. this study's aim was to advance how ecological information may be incorporated into the stream restoration design process. 2. Nine mesohabitat units were designated, including pool-front, -mid, and -rear units, scour pool, simple and complex riffles, glide, submerged point bar. and channel expansion marginal deadwater. Physical habitat structure differed among the nine mesohabitat units by length, water depth, and bed slope and complexity. Fish were collected in specific unit volumes by use of prepositioned areal electrofishing devices. in which distinct patterns of fish mesohabitat use were observed. 3. A key finding was the differences in fish assemblages among the pool units, in which fish densities were greatest in the pool-front and scour pool units. Also, fish density in the pool-front unit was positively correlated with pool entrance slope. Biomass was greatest ill the pool-front mid -mid units. and it was correlated with maximum mid-pool depth. Density and biomass were generally lowest ill the pool-rear unit. Other unique relationships were also observed among the mesohabitat units. 4. Based oil feeding guild, patterns of fish mesohabitat use were observed for this summer low-flow periods insectivores dominantly Used pool-Front and scour pool units. herbivores dominantly Used complex riffle Units. and piscivores Used pool-front and -mid units. 5. Useful ecological information was derived from fish species-habitat relationships observed ill this study. linking mesohabitat units with species requirements tor food resources. Such findings support advancements to ecological design strategies for stream restoration that promote hydraulic habitat diversity. Copyright (C) 1008 John Wiley & Sons. Ltd.