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

Abstract

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.

Whole-lake food web model indicates alewife invasion fueled lake trout restoration and altered patterns of trophic flow Lake Champlain

“…These estimates were created by applying age-specific survival rates to annual stocking records to produce abundance-at-age estimates for each year in the study period. Three different sets of survival estimates were used depending on the time period: (1) for 1980-1987, survival estimates were taken from Plosila and Anderson (1985), who estimated low adult (ages 5+) survival using synthetic cohort analysis applied to lake trout caught in standardized gillnet surveys and aged using a combination of hatchery fin clips and scales; (2) for 1988-2000, survival estimates were taken from Marsden et al (2003) who used an updated version of the same dataset to assess the impact of sea lamprey control, finding that control had a positive impact on survival of early-adult (ages 3-4) and adult fish; and (3) for 2000-2022, survival estimates were taken from Hemmelgarn et al (2022) who used standardized bottom trawl surveys and a combination of hatchery fin clips and maxillary age estimates to estimate survival for juveniles (ages 1-3), early-adult, and adult lake trout. Adult survival was much greater over 2000-2022 compared to earlier periods (Hemmelgarn et al, 2022).…”

“…Three different sets of survival estimates were used depending on the time period: (1) for 1980-1987, survival estimates were taken from Plosila and Anderson (1985), who estimated low adult (ages 5+) survival using synthetic cohort analysis applied to lake trout caught in standardized gillnet surveys and aged using a combination of hatchery fin clips and scales; (2) for 1988-2000, survival estimates were taken from Marsden et al (2003) who used an updated version of the same dataset to assess the impact of sea lamprey control, finding that control had a positive impact on survival of early-adult (ages 3-4) and adult fish; and (3) for 2000-2022, survival estimates were taken from Hemmelgarn et al (2022) who used standardized bottom trawl surveys and a combination of hatchery fin clips and maxillary age estimates to estimate survival for juveniles (ages 1-3), early-adult, and adult lake trout. Adult survival was much greater over 2000-2022 compared to earlier periods (Hemmelgarn et al, 2022). The transition point between the first two estimates was set at the midpoint between the years for which they produced estimates, while the choice of 2000 as a transition between the second and third set was based on the observation of a marked increase in contemporary catches from the 2000 cohort forward (Marcy-Quay, unpublished data).…”

“…The transition point between the first two estimates was set at the midpoint between the years for which they produced estimates, while the choice of 2000 as a transition between the second and third set was based on the observation of a marked increase in contemporary catches from the 2000 cohort forward (Marcy-Quay, unpublished data). As no historical records of juvenile survival were available, survival rates for all years were set to the values estimated by Hemmelgarn et al (2022). Estimates of abundance for all years were then transformed to estimates of biomass using the length-at-age and weight-length relationships estimated by Hemmelgarn et al (2022).…”

“…As no historical records of juvenile survival were available, survival rates for all years were set to the values estimated by Hemmelgarn et al (2022). Estimates of abundance for all years were then transformed to estimates of biomass using the length-at-age and weight-length relationships estimated by Hemmelgarn et al (2022). All datasets were assessed for goodness-of-fit based on RSME of long-term data to predicted output (Kao et al 2016), and by visual comparison to the modelderived food web dynamics.…”

Investigations of Lake Trout Salvelinus namaycush Ecology and Behaviour in Relation to Fragmented Thermal Habitats to Inform a Multifaceted Management Strategy

“…Maxillaries have been used as a non-lethal sampling method to estimate Lake Trout age (Wellenkamp et al 2018;Hemmelgarn et al 2022). Maxillaries were exposed to >80 °C water for ~15 s to remove tissue and expose the bone.…”