Seasonal Sampling Influence on Population Dynamics and Yield of Channel Catfish and Walleye in a Large Great Plains Reservoir

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.

Enhanced inference of ecological networks by parameterizing ensembles of population dynamics models constrained with prior knowledge

Background

Accurate network models of species interaction could be used to predict population dynamics and be applied to manage real world ecosystems. Most relevant models are nonlinear, however, and data available from real world ecosystems are too noisy and sparsely sampled for common inference approaches. Here we improved the inference of generalized Lotka–Volterra (gLV) ecological networks by using a new optimization algorithm to constrain parameter signs with prior knowledge and a perturbation-based ensemble method.

Results

We applied the new inference to long-term species abundance data from the freshwater fish community in the Illinois River, United States. We constructed an ensemble of 668 gLV models that explained 79% of the data on average. The models indicated (at a 70% level of confidence) a strong positive interaction from emerald shiner (Notropis atherinoides) to channel catfish (Ictalurus punctatus), which we could validate using data from a nearby observation site, and predicted that the relative abundances of most fish species will continue to fluctuate temporally and concordantly in the near future. The network shows that the invasive silver carp (Hypophthalmichthys molitrix) has much stronger impacts on native predators than on prey, supporting the notion that the invader perturbs the native food chain by replacing the diets of predators.

Conclusions

Ensemble approaches constrained by prior knowledge can improve inference and produce networks from noisy and sparsely sampled time series data to fill knowledge gaps on real world ecosystems. Such network models could aid efforts to conserve ecosystems such as the Illinois River, which is threatened by the invasion of the silver carp.

Population Characteristics of Yellow Perch in a Central Appalachia Hydropower Reservoir

Estimates of population characteristics of sport fishes inform fisheries management decisions and provide feedback on management strategies. Cheat Lake provides an unusual fishery in West Virginia because the hydropower reservoir supports a Yellow Perch Perca flavescens population. We estimated age structure, size structure, condition, total instantaneous mortality, growth, and summer diet for Cheat Lake Yellow Perch based on electrofishing collections in 2012. From 302 individuals, we observed a maximum age of 9 y. Maximum age, average size, and growth of females in the sample exceeded those of males. Cheat Lake Yellow Perch scored low on the relative weight index, but generally exhibited faster growth than other populations, even when compared by sex. Estimated annual survival was 0.63 (95% CI = 0.51–0.78), which is comparable to other exploited populations. These data support the presence of an ontogenetic diet shift from consumption of zooplankton to macroinvertebrates and fishes as Yellow Perch age. This study is the first evaluation we are aware of on Yellow Perch population characteristics in West Virginia, providing baseline data to enhance management decisions and direct future studies.