DOES ANNUAL VARIATION IN GROWTH AND SEXUAL-MATURATION OF WHITE SUCKER(CATOSTOMUS-COMMERSONI) CONFOUND COMPARISONS BETWEEN PULP-MILL CONTAMINATED AND REFERENCE RIVERS

A previous study on the effect of pulp and paper effluents on white su cker (Catostomus commersoni), conducted in 1991 and 1992, in both effl uent-exposed and reference rivers showed that fish grew faster at down stream sites than at upstream sires. However. in contrast with fish fr om a reference river, fish exposed to effluent showed no decrease in a ge or size at first maturity or increase in gonad size or fecundity in response to greater growth. The objective of the present study, condu cted in 1993. was to test if differences in measures of growth and sex ual maturation between fish populations in exposed and reference river s would vary from year to year and whether such variation would affect conclusions concerning the effects of pulp mill effluents. Although s ize at age, fecundity. and age at first maturity varied between the tw o studies, patterns of demographic responses to pulp mill effluents, r elative to reference populations, remained the same, i.e., conclusions about effects of pull, mill effluents did not change despite variatio n in demographic variables between years and sites. This study reaffir med the view that only by including the fish populations in a referenc e river could effects due to bleached kraft mill effluent be separated from effects due to nutrient gradients.