| Popis: |
Fish samples collected during different times of the year can be subject to various biases, but the influence of sampling during different seasons on population dynamics and yield metrics in large reservoirs is not well reported. This study compared the age structure, growth, mortality, and yield estimates of Channel Catfish Ictalurus punctatus and Walleye Sander vitreus collected during spring and fall with standardized gill netting in a large Nebraska, USA, reservoir. We sampled fish by using the Nebraska Game and Parks Commission standardized gill net survey methodology. We estimated ages from pectoral spines of Channel Catfish and from sagittal otoliths of Walleye, derived age-length keys, and compared mean spring and fall ages with t-tests. We compared spring and fall von Bertalanffy growth curves with likelihood-ratio tests and mortality estimates from weighted catch curves with an analysis of variance. We visually compared spring and fall yield estimates derived from yield-per-recruit models to assess the impact of variable population dynamics estimates. Estimates of mean age, growth coefficient, mean asymptotic length, total annual mortality, and yield of Channel Catfish did not differ between spring and fall. Conversely, older age structure of Walleye in spring resulted in lower estimates of total annual mortality and higher yield than in fall. Estimates of mean asymptotic length and growth coefficient differed between spring and fall for female Walleye, and mean asymptotic length, growth coefficient, and theoretical time at age 0 estimates varied between spring and fall for male Walleye. Fall yield estimates were substantially lower than spring estimates for both male and female Walleye. These results demonstrate that the sample collection season can impact population dynamics estimates for certain species, whereas others remain relatively unaffected. |
