Interactions between young-of-the-year exotic rainbow smelt and native yellow perch in a northern temperate lake

Yellow perch Perca flavescens recruitment in Crystal Lake, Vilas County, Wi sconsin, has declined since the exotic rainbow smelt Osmerus mordax increas ed in abundance. The yellow perch population is in decline because of low j uvenile survival. However, diet analyses indicate that predation by adult s melt does not appear to be the cause. We investigated interactions between age-0 yellow perch and age-0 rainbow smelt by comparing changes in abundanc e and distributions. maximum mouth gapes, and the amount and type of prey e aten. During 1995 and 1996, age-0 smelt and perch hatched at similar times, had similar spatial distributions, and preferred similar prey. Diet overla p exceeded 45% on all sampling dates during the spring and summer of 1995 a nd 1996 and exceeded 60% on all but the first and last sampling dates in 19 96. Two species of Diaptomus were the preferred prey of both smelt and perc h, although smelt ate more of the larger size-classes than did perch throug hout 1996. Consumption by smelt may have led to a decline in Diaptomus duri ng the early summer of 1996. Estimates of temperature, hatch date, and grow th derived from a long-term data set were used as input for bioenergetics s imulations that estimated the proportion of maximum attainable consumption realized by the average age-0 perch in each year, when they occurred, betwe en 1981 and 1996. During 1995 and 1996. years where age-0 smelt and perch w ere documented together, the proportion of maximum attainable consumption w as significantly below that of any successful year-class observed during th e long-term record. Age-0 perch did not survive in measurable numbers throu gh the entire summer in either 1995 or 1996. Exploitation competition betwe en age-0 perch and smelt may reduce the likelihood of strong year-classes o f yellow perch when year-classes of rainbow smelt occur.