Catch me if you can: Temporal sampling changes inferences of Smallmouth Bass population structure
Robert D Allison, Melissa R Wuellner, Alexander D Engel, Keith D Koupal, Brian G BlackwellAbstract
Objective
Standardized assessments of sport fish populations are essential for providing fisheries managers with reliable population data to make management decisions concerning recreational fisheries. However, changes within and outside of a water body can influence catch and, therefore, assessments of populations both within and between years. The objective of this study was to evaluate seasonal and interannual variability in Smallmouth Bass Micropterus dolomieu population indices to identify optimal sampling periods for conducting a standardized population assessment in a large Nebraska irrigation reservoir.
Methods
Smallmouth Bass were sampled monthly from May to October of 2024 and 2025 in Lake McConaughy, Nebraska, using nighttime boat-mounted electrofishing at six fixed stations. Length and weight were recorded for all sampled fish. Population characteristics were assessed each month using CPUE, relative size distribution, young–adult ratio, and relative weight (Wr). Indices were evaluated across months, seasons (i.e., spring, summer, and fall), and years.
Results
A total of 1,436 Smallmouth Bass were collected across both years. Overall, CPUE was lower in 2025 than in 2024. Monthly CPUE varied between years, particularly in July and August. Monthly mean CPUE ranged from 15 to 216 fish/h across both years, with catch generally lower in spring and increasing through summer and fall. Seasonal patterns were similar for our three relative size distribution metrics and the young–adult ratio, whereby larger fish were found more frequently in spring samples and smaller fish were more abundant in summer and fall samples. Mean Wr by month and year varied between 86 and 105. Values of Wr were higher in the first year compared with the second year, higher in spring compared with the other two seasons, and higher for sub-stock-sized fish compared with stock-sized and larger individuals, likely reflecting differences in prey availability, metabolic demand, and gonadal development throughout the growing season.
Conclusions
Despite seasonal and interannual variability, population indices for Smallmouth Bass in Lake McConaughy were consistent with patterns observed in other North American systems. Results indicate that the timing of sampling can influence perceived population structure and status. Spring sampling may better assess the adult fish population, whereas fall sampling may be better for sampling young (age-1) fish or indexing recruitment. Biannual sampling could be used to achieve both sampling goals, but consideration of the time and money resources to conduct sampling efforts may require managing agencies to prioritize the types of information they desire from the population.