Contemporary Growth and Survival of Stocked and Wild Lake Trout in Lake Champlain Evaluated Using Maxillary Age Estimates

The population of Lake Trout Salvelinus namaycush in Lake Champlain has been sustained by stocking since 1973, but natural recruitment of wild fish has been observed since 2012. By 2020, continued recruitment and maturation of wild year-classes indicated that updated population parameters were needed to assess and adjust management practices. Age estimation from historical methods (fin clips and scales) was undependable due to crowding of annuli in older fish and the inability to verify uncertain age estimates using a 5-year fin clip rotation for older fish. We used maxillary bones to obtain precise and accurate age estimates for adult wild and stocked fish. In combination with preadult ages derived from fin clips and length-frequency analysis, we estimated the contemporary survival and growth of juvenile (age 2-3), early-adult (age 3-4), and adult (age 5+) Lake Trout in Lake Champlain. The precision and accuracy of our maxillary age estimates were greater than or comparable to the precision and accuracy of otolith and maxillary age estimates of Lake Trout populations in the Great Lakes. Estimates of Lake Trout growth suggested that stocked and wild fish grew at different rates, with stocked fish having an early size advantage but ultimately reaching a similar maximum size. There were no significant differences in length-weight relationships between stocked and wild fish. Estimates of adult survival were slightly greater than range-wide averages and well above recent estimates for stocked populations in the Great Lakes. Juvenile and early-adult survival estimates were similar to each other and both far lower than adult estimates. Stocked and wild fish had similar survival rates in all age-classes. Ultimately, the use of maxillary bones allowed us to make better estimates of contemporary population parameters necessary for informing management decisions.