Lake Sturgeon Growth and Mortality Assessment in the Face of Age Estimate Variability

The lower Niagara River is home to one of the remaining populations of Lake Sturgeon in Lake Ontario and is the location of an intensive population assessment study.  A major component of effective population assessment relies on accurate ageing techniques.  The non-lethal method of age assignment based on counting annuli formed in pectoral spines has been used extensively for Lake Sturgeon. Once an age is estimated and length and weight measurements are taken, one can apply the data to models that estimate parameters important for characterizing populations.  Two important models, the von Bertalanffy growth model and the linear catch curve model, derive parameters such as the growth coefficient, asymptotic length, and mortality rate for the studied population.    In this study, five readers estimated ages of fish using images of pectoral spine cross-sections.  Estimated ages were compared to determine patterns of reader agreement.  Using these ages, we ran models to investigate the sensitivity of model parameters to among-reader variation in age estimates.  Results show the effect of reader variation on parameter estimates and the relative outcome in terms of interpreting the results.