Estimating downstream passage efficiency for an endangered species

We conducted an analysis of physical and behavioral exclusion of shortnose sturgeon using morphometric and laboratory to estimate the fish passage efficiency of an exclusion rack with 2-inch clear spacing installed at the Hadley Falls Project.  Morphometric data indicated that the percent of sturgeon physically small enough to pass through a 2-inch bar spacing is 100% for fork lengths less than 350 mm, approximately 50% for fish between 350 and 510 mm, and 0% for fish greater than 510 mm.  The laboratory data indicated fish length was inversely related to entrainment rates and positively correlated with approach velocity, and entrainment of all size groups was less than predicted by length only.  The estimates of physical and behavioral exclusion were combined with predicted turbine survival rates for the Hadley Falls turbines to estimate overall fish passage efficiency for fish passing downstream of the project.  Based on this analysis, overall fish passage efficiencies should be between approximately 90 and 98% for shortnose sturgeon less than 510 mm and 100% for fish greater than this length.