Estimating Age-at-Maturity from Length-at-Age: A Biphasic Modeling Approach

Fitting a von Bertalanffy (vB) growth model to lifetime growth in length does not adequately account for biological mechanisms. The Lester model of biphasic growth is a viable and biologically realistic alternative to the vB model that is grounded in life-history theory. It explicitly accounts for the shift in energy allocation that occurs at maturity and allows for estimation of additional, biologically relevant parameters (e.g., reproductive investment, natural mortality). Currently, the Lester model is limited to datasets for which age-at-maturity has been estimated. However, if immature and mature growth differ, then it should be possible to use the Lester model to both describe lifetime growth and estimate age-at-maturity. To test this prediction, we (1) applied maximum likelihood profiling to simulated growth trajectories to determine when ‘blind’ Lester model fitting is feasible, and (2) constructed a decision tree to guide the application of the method. We validated these results using walleye Sander vitreus data from Minnesota, Ontario (CA), and Quebec (CA). The ability to estimate biphasic model parameters from only length-at-age data has important implications for both research (e.g., fisheries-induced evolution) and management.