Investigations into the Relationships between Fish Impingement and Fish Health

Various 316(b) research projects, sponsored by Alabama Power Company (APC), were initiated in 2004 to investigate the relationship between fish impingement and fish health.  These projects used fish health assessments, Acoustic Doppler Current Profiling (ADCP) and hydroacoustic technologies. Most of these studies were conducted at Plant Barry which is located on the lower Mobile River.  While the scope of these projects varied, initial sampling indicated the species impinged with greatest frequency and mitigation value were threadfin shad, freshwater drum, blue catfish, and channel catfish.  Therefore, these species were chosen for further fish health examination to test the hypothesis that impingement may select for unhealthy individuals from the natural environment.  Fish health examinations included necropsies for prevalence of bacterial and parasitic infections.  Impinged fish were compared to open-water fish obtained from within 2.4 km of the vicinity of the cooling water intake structure (CWIS) and to fish collected from inside the CWIS (screen pit).  Results of this study support the general hypothesis that impingement may select for unhealthy fish.  However, the high biomass and high density of relatively healthy fish found in the screen pit supports the hypothesis that impingement may select for “naturally” unhealthy individuals from the hydraulic zone of influence (HZI).  Another investigation into the relationship between the volume of the HZI, the through-screen velocity and the amount of impingement at various power plants suggests a potential confounding effect between the HZI and through-screen velocities.  Furthermore, studies using hydroacoustics to monitor fish movement inside the CWIS also suggest that free movement exists for many fish in and out of the CWIS on a diurnal basis.  Results of these studies indicate that the cause and effect relationships concerning fish impingement requires further study and may be justified due to the expense and questionable results of various mitigation options.