MATURATION OF WHITE SUCKER, CATOSTOMUS-COMMERSONI, POPULATIONS IN ONTARIO

White sucker, Catostomus commersoni, were sampled from 13 Ontario lakes. Two growth parameters (growth rate in length as dL/dt at age t(0) and age at maximum growth rate in weight as dW/dt) were estimated by fitting length- and weight-at-age data to the two reparameterized von Bertalanffy growth functions for each of 13 populations. Two maturation parameters (length and age at 50% maturity, ML and MA) were estimated using the linear regression method for both sexes. Two regression approaches were used in analyzing experimental data: a traditional geometric means (GM) method and a two-step procedure of robust regression analysis which includes applying the least median squares method to identify possible outliers and applying the GM method to data exclusive of the defined outliers. Great among-population variation in the estimated growth and maturation parameters was observed for both female and male white sucker. White sucker growing faster at young ages tended to mature earlier. High population density might result in white sucker having slower growth rates in their earlier ages and larger MA's. This study indicated that maturation of white sucker is food dependent, and early growth rate is an important factor in determining the timing of maturity.