Yellow Perch Dynamics in Southwestern Lake Michigan during 1986–2002

Abstract

We examined the role of harvest in the collapse of the population of yellow perch Perca flavescens in southwestern Lake Michigan during the mid to late 1990s. After the great decrease in this population at that time, commercial fisheries in Illinois and Wisconsin were closed during 1996–1997 (and have remained closed), and stricter regulations were placed on recreational fisheries. Reproductive failure has been implicated as the primary cause of the population collapse, but the role of fishing in the collapse was not rigorously investigated in previous studies. We conducted an age-, size-, and sex-structured stock assessment of yellow perch to estimate population size and examine historical trends in fishing mortality in Illinois and Wisconsin waters of southwestern Lake Michigan. Model estimates indicated that yellow perch abundance in 2002 was less than 10% of the 1986 abundance in Wisconsin and about 20% of the respective population in Illinois. Annual mortality rates for females age 4 and older averaged 69% during 1986–1996 in Wisconsin and 60% in Illinois during 1986–1997, rates that are quite high for a species like yellow perch, which can live longer than 10 years. The estimated fishing mortality rates of adult females during 1986–1996 exceeded widely used reference points, suggesting that overfishing may have occurred. Fishing mortality rates decreased substantially in the late 1990s after stricter regulations were imposed on recreational fisheries and commercial fisheries were closed. We believe that unsustainably high mortality rates from fishing were a substantial contributing cause of the rapid decline of mature females in the mid-1990s. Spawning stock biomass in 2002 was at its highest level since the early 1990s despite relatively poor recruitment during the past decade. In part, this development reflects the fact that management actions have successfully reduced fishing mortality.