Laboratory Studies to Evaluate Survivorship of Fish Early Life Stages Upon Passage by Hydrokinetic Rotor-Blade Profiles

Many hydrokinetic (HK) energy projects have been proposed for large rivers in the U.S., and there is concern about the susceptibility of riverine fish to rotor blade strike.  The survival of early-life stage fish that encounter HK rotor blades is currently unknown.  This laboratory study examined the survival of striped bass early-life stages after encountering different stationary blade profiles.  The fish were entrained in current velocities of 0.85 m/sec or 1.15 m/sec, representative of the lower velocities found near the hub or mid-blade of an HK rotor.  We quantified both immediate and delayed mortalities among fish resulting from contact or passage by the blade and through the turbulent flows in wake of the blade. Survivorship of striped bass larvae and juveniles was inversely related to current velocities approaching the blades.  Survivorship varied among exposure to different blade profiles and suggested that for young fish the risk of blade strike from the leading edge may be less important than exposure to the turbulent flows in the wake of the blades.  Further laboratory studies would benefit from more realistic conditions (e.g., moving blades and faster approach velocities) and facilitate incorporating these estimates of passage mortality into assessments of impacts on fish populations.