1. Introduction Walleye (Stizostedion vitreum vitreum) and yellow perch (Perca flavescens) co-occur in many central North American lakes and often form a tightly cou- pled predator-prey species pair (Forney 1980, Post & Rudstam 1992). Our current understanding of these species’interactions is based partly on long term studies in Oneida Lake, New York, by John Forney and co-workers (e.g. Forney 1976, 1977, 1980, Mills & Forney 1988). When walleye are abundant (as in Oneida Lake), they are the main predator on young- of-year yellow perch (YOY perch). YOY perch are vulnerable to walleye predation once they reach a total length of 18 mm and walleye often consume a large portion of the YOY perch population during Ann. Zool. Fennici 33: 443–449 ISSN 0003-455X Helsinki 28 November 1996 © Finnish Zoological and Botanical Publishing Board 1996 Evidence of interactions between walleye and yellow perch in New York State lakes Lars G. Rudstam, David M. Green, John L. Forney, Douglas L. Stang & Joseph T. Evans Rudstam, L. G., Green D. M. & Forney, J. L., Cornell Biological Field Station and Department of Natural Resources, Cornell University, 900 Shackelton Point Road, Bridgeport, NY, 13030, USA Stang, D. L., New York State Department of Environmental Conservation, 50 Wolf Road, Albany, NY, 12233, USA Evans, J. T., New York State Department of Environmental Conservation, 128 South Street, Olean, NY, 14414, USA Received 21 August 1995, accepted 28 November 1995 We believe that the population dynamics of walleye (Stizostedion vitreum vitreum) and yellow perch (Perca flavescens) are strongly affected by biotic interactions: abundant walleye populations limit perch recruitment, resulting in fast perch and slow walleye growth rates; sparse walleye populations allow for strong perch recruitment resulting in slow yellow perch and fast walleye growth rates. If these mechanisms are important, we would expect a negative correlation between perch and walleye growth rates. Mean length at age 4 for walleye and yellow perch in 23 New York waters were negatively correlated. Further, changes over time in length at age of both species as walleye populations increased in Canadarago and Silver Lakes follow the regression from the whole data set. This indicates a strong interaction between these two percid species in New York waters. The residuals were affected by lake productivity, but not lake area or mean depth. Waters with very low productivity had smaller walleye and yellow perch than expected from the regression.