Seasonal Variations in GSI for Yellow Perch in Southern Lake Michigan

Yellow perch (Perca flavescens) were collected from 2009 to 2012 using gill nets set at four sites in the Indiana waters of southern Lake Michigan to determine how gonadal somatic index (GSI) varied before, during and after spawning. The largest GSI was found during the pre-spawning period in May and ranged between 16 and 26% for females. A steep drop occurred in mid-May immediately following spawning to approximately 1%.  Similar reductions following spawning also occurred for males. No change was seen in GSI through August in each year, suggesting that time immediately after spawning is solely devoted to recovery and growth.