Effectiveness of Fine Mesh Cylindrical Wedge-Wire Screens in Reducing Entrainment of Lake Michigan Ichthyoplankton

Samples of ichthyoplankton entrained through 2.0-mm and 9.5-mm-slot opening cylindrical wedge-wire screens and through an open pipe (control) were collected in June, July, and August 1979, 1067 m off the southeast shore of Lake Michigan at a depth of 10.7 m. Screens were designed for a flow rate of 1.9 m3 min−1 at 15.2 cm s−1 through slot velocity. Ambient composition and density of ichthyoplankton were determined by net tows. Rainbow smelt (Osmerus mordax), alewife (Alosa pseudoharengus), and yellow perch (Perca flavescens) larvae were common in both entrainment and tow collections. Eggs were found almost exclusively in entrainment collections. Ambient larval fish densities were about 11 times greater than those found in entrainment collections. Total entrainments through either screen and the open pipe were not statistically significant. Larval avoidance and, to a lesser extent, screen exclusion were responsible for the low entrainment. We estimated that about 90% of native fish larvae at the site avoided pumping.Key words: Lake Michigan, fish larvae, fish eggs, ichthyoplankton, entrainment, power plants, avoidance