RELATIONSHIPS OF LITTORAL FISH ABUNDANCE TO WATER CHEMISTRY AND MACROPHYTE VARIABLES IN CENTRAL ONTARIO LAKES

We collected data on the most frequently encountered medium- to large- bodied littoral fishes in two independent sets of central Ontario lake s; the first set (10 lakes) was sampled between 1979 and 1980 and the second (15 lakes) from 1982 to 1988. Empirical models were constructed by correlating the strongest within-year, among-lake trends in specie s abundance with the strongest among-lake trends in abiotic variables determined by principal coordinates analyses; indices of nearshore veg etation cover were also used as predictor variables. From 1982 to 1988 , variation in abundance of Lepomis (pooled pumpkinseed (L. gibbosus) and bluegill (L. macrochirus)) was the major among-lake trend, and thi s was strongly correlated with differences in lake primary productivit y (P < 0.02 for each year) and nearshore macrophyte cover (P < 0.03 fo r each year). In 1979-80, variation in abundance of pumpkinseed was th e major among-lake trend, and this was strongly correlated with among- lake variability in nearshore macrophyte cover (P = 0.006) and lake fl ushing rate (P = 0.008); bluegill were not present in these lakes. Amo ng-lake variation in food availability and/or abundance of refuges fro m predators may be factors responsible for the among-lake patterns in Lepomis abundance.