A Comparison of the Scale and Otolith Methods of Age Estimation for Lake Whitefish in Lake Huron

Abstract

AbstractWe compared sagittal otolith and scale age estimation methodologies for lake whitefish Coregonus clupeaformis collected in Georgian Bay and the main basin of Lake Huron between 2002 and 2004 in terms of the age, growth, and mortality estimates generated by the two methodologies. In general, otolith age estimates were higher than scale age estimates. Forty‐nine percent of the fish aged by otoliths were judged to be greater than 10 years of age, compared with 5% of the fish aged by scales, and more age‐classes were found when otoliths were used. Otolith and scale ages agreed for 16% (n = 60) of Georgian Bay fish and only 9% (n = 27) of main‐basin fish. The overall coefficients of variation for the otolith and scale age estimation methodologies pooled across years and basins were 5.52% and 2.68%, respectively. Mean length at age based on otoliths was significantly lower than mean length at age based on scales. Variation in the mean length at age was greatest for fish age 7 and older. Otolith‐based catch‐curve estimates of total instantaneous mortality (Z) were 1.26 in Georgian Bay and 0.57 in the main basin. In contrast, scale‐based estimates of Z were 0.98 for Georgian Bay and 0.85 for main‐basin lake whitefish. This study has demonstrated that estimates of age, growth, and mortality for lake whitefish in Lake Huron vary according to aging methodology. Therefore, we recommend that mark–recapture studies be undertaken to validate the spatiotemporal variation in lake whitefish age estimates in Lake Huron.