Seasonal microhabitat selectivity by juvenile steelhead in a central California coastal river

Microhabitat data were collected at focal positions of juvenile steelhead trout (Oncorhynchus mykiss) in the Big Sur River, California during spring, summer, and fall. An equal-area sampling approach was used to guide fish surveys and allocate habitat availability sampling among seasons, river reaches, and mesohabitat types. Juvenile steelhead trout habitat selection changed with fish size, season, discharge, and habitat availability. Water depth and water velocity were of primary importance in habitat selection for all size groups of rearing steelhead. Habitat Suitability Criteria (HSC) were prepared for water depth, mean water velocity, focal velocity, specific escape cover types, and distance to in-water escape cover to reflect seasonal habitat selectivity for rearing steelhead. Habitat "preference" HSC (use adjusted for availability using the U/A forage ratio) were also developed and compared with the equal-area selectivity HSC and with habitat availability. The U/A results produced extreme shifts in maximum suitability for several curves, and perhaps more significantly the U/A ratios severely deflated suitabilities where the majority of the fish were observed. With proper habitat stratification and non-limiting sampling conditions (e.g., adequate flows and non-degraded habitat), use of an equal-area sampling design for site-specific selectivity HSC development was determined to be a viable option for development of biologically relevant and representative HSC, and apt for effective environmental flow recommendations.