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 reservoir. Fish were sampled using the Nebraska Game and Parks Commission standardized gill net survey methodology. Ages were estimated from pectoral spines of Channel Catfish and sagittal otoliths of Walleye, age-length keys were derived, and mean spring and fall ages were compared with t -tests. Spring and fall von Bertalanffy growth curves were compared with likelihood-ratio tests, and mortality estimates from weighted catch curves were compared with an analysis of variance. Spring and fall yield estimates derived from yield-per-recruit models were visually compared to assess the impact of variable population dynamics estimates. Estimates of mean age, growth coefficient ( K ), mean asymptotic length ( L ∞ ), total annual mortality ( A ), 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 A and higher yield than in fall. Estimates of L ∞ and K differed between spring and fall for female Walleye, and L ∞ , K , and t 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 season when samples are collected can impact population dynamics estimates for certain species while others remain relatively unaffected.
Monitoring plan for mercury in fish tissue and water from the Boise River, Snake River, and Brownlee Reservoir, Idaho and Oregon