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, Wisconsin, has declined since the exotic rainbow smelt Osmerus mordax increased in abundance. The yellow perch population is in decline because of low juvenile survival. However, diet analyses indicate that predation by adult smelt does not appear to be the cause. We investigated interactions between age-0 yellow perch and age-0 rainbow smelt by comparing changes in abundance and distributions, maximum mouth gapes, and the amount and type of prey eaten. During 1995 and 1996, age-0 smelt and perch hatched at similar times, had similar spatial distributions, and preferred similar prey. Diet overlap exceeded 45% on all sampling dates during the spring and summer of 1995 and 1996 and exceeded 60% on all but the first and last sampling dates in 1996. Two species of Diaptomus were the preferred prey of both smelt and perch, although smelt ate more of the larger size-classes than did perch throughout 1996. Consumption by smelt may have led to a decline in Diaptomus during the early summer of 1996. Estimates of temperature, hatch date, and growth derived from a long-term data set were used as input for bioenergetics simulations that estimated the proportion of maximum attainable consumption realized by the average age-0 perch in each year, when they occurred, between 1981 and 1996. During 1995 and 1996, years where age-0 smelt and perch were documented together, the proportion of maximum attainable consumption was significantly below that of any successful year-class observed during the long-term record. Age-0 perch did not survive in measurable numbers through the entire summer in either 1995 or 1996. Exploitation competition between age-0 perch and smelt may reduce the likelihood of strong year-classes of yellow perch when year-classes of rainbow smelt occur.