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Invasive rainbow smelt (Osmerus mordax) have spread rapidly throughout inland lakes of North America with detrimental effects on several native fishes. To test for the potential to control this species, we conducted an experimental removal of rainbow smelt in Sparkling Lake, Wisconsin during 2002–2009. We combined intensive spring harvest of rainbow smelt with an effort to increase predation on this invasive through restricted angler harvest of walleye and increased stocking of walleye (Sander vitreus). Over 4,170 kg of rainbow smelt were harvested during the experiment; up to 93% of adults were removed annually. We observed a significant decline in rainbow smelt gillnet catches during the removal. However, rainbow smelt relative abundances began increasing upon cessation of the removal effort. Bioenergetics modeling suggested that despite achieving higher than the regional average walleye densities, walleye consumed only a fraction of the rainbow smelt standing stock biomass. Our findings suggest that removal of rainbow smelt from invaded lakes may be difficult, and reinforce the importance of prevention as a strategy to limit the expansion of this invasive fish.

Increasing anthropogenic turbidity is among the most prevalent disturbances in freshwater ecosystems, through increases in sedimentary deposition as well as the rise of nutrient-induced algal blooms. Changes to the amount and color of light underwater as a result of elevated turbidity are likely to disrupt the visual ecology of fishes that rely on vision to survive and reproduce; however, our knowledge of the mechanisms underlying visual responses to turbidity is lacking. First, we aimed to determine the visual detection threshold, a measure of visual sensitivity, of two ecologically and economically important Lake Erie fishes, the planktivorous forage fish, emerald shiner ( ), and a primary predator, the piscivorous walleye ( ), under sedimentary and algal turbidity. Secondly, we aimed to determine if these trophically distinct species are differentially impacted by increased turbidity. We used the innate optomotor response to determine the turbidity levels at which individual fish could no longer detect a difference between a stimulus and the background (i.e. visual detection threshold). Detection thresholds were significantly higher in sedimentary compared to algal turbidity for both emerald shiner (mean ± SE = 79.66 ± 5.51 NTU, mean ± SE = 34.41 ± 3.19 NTU) and walleye (mean ± SE = 99.98 ± 5.31 NTU, mean ± SE = 40.35 ± 2.44 NTU). Our results suggest that across trophic levels, the visual response of fishes will be compromised under algal compared to sedimentary turbidity. The influence of altered visual environments on the ability of fish to find food and detect predators could potentially be large, leading to population- and community-level changes within the Lake Erie ecosystem.

Future changes to climate in the Great Lakes may have important consequences for fisheries. Evidence suggests that Great Lakes air and water temperatures have risen and the duration of ice cover has lessened during the past century. Global circulation models (GCMs) suggest future warming and increases in precipitation in the region. We present new evidence that water temperatures have risen in Lake Erie, particularly during summer and winter in the period 1965–2000. GCM forecasts coupled with physical models suggest lower annual runoff, less ice cover, and lower lake levels in the future, but the certainty of these forecasts is low. Assessment of the likely effects of climate change on fish stocks will require an integrative approach that considers several components of habitat rather than water temperature alone. We recommend using mechanistic models that couple habitat conditions to population demographics to explore integrated effects of climate-caused habitat change and illustrate this approach with a model for Lake Erie walleye (Sander vitreum). We show that the combined effect on walleye populations of plausible changes in temperature, river hydrology, lake levels, and light penetration can be quite different from that which would be expected based on consideration of only a single factor.

Phenotypic change in closely related lineages frequently follows a common pathway in response to similar environmental conditions. This process, termed parallel evolution, results in the evolution of similar but independently derived ecotypes. Individuals with a blue phenotype are observed in some populations of walleye (Sander vitreus) from Laurentian Shield lakes. The blue phenotype may represent a case of parallel evolution: previous morphological studies revealed significant differences compared with the yellow phenotype as well as numerous lake-specific characteristics among blue individuals. The genetic variability of blue and yellow walleye phenotypes from 6 Laurentian Shield lakes was estimated using AFLP. Results clearly indicate that, whatever their phenotype, individuals from a given lake were more similar genetically than those from other lakes. However, blue and yellow phenotypes represent different populations within each lake. These results suggest the colonization of each lake by a single group of walleye followed by the parallel origin of the blue phenotype. The parallel evolution of the blue walleye phenotype could represent an excellent model for studying mechanisms underlying divergent selection and reproductive isolation.

Recreational fisheries are valued at $190B globally and constitute the predominant way in which people use wild fish stocks in developed countries, with inland systems contributing the main fraction of recreational fisheries. Although inland recreational fisheries are thought to be highly resilient and self-regulating, the rapid pace of environmental change is increasing the vulnerability of these fisheries to overharvest and collapse. Here we directly evaluate angler harvest relative to the biomass production of individual stocks for a major inland recreational fishery. Using an extensive 28-y dataset of the walleye (Sander vitreus) fisheries in northern Wisconsin, United States, we compare empirical biomass harvest (Y) and calculated production (P) and biomass (B) for 390 lake year combinations. Production overharvest occurs when harvest exceeds production in that year. Biomass and biomass turnover (P/B) declined by ∼30 and ∼20%, respectively, over time, while biomass harvest did not change, causing overharvest to increase. Our analysis revealed that ∼40% of populations were production-overharvested, a rate >10× higher than estimates based on population thresholds often used by fisheries managers. Our study highlights the need to adapt harvest to changes in production due to environmental change.

Purpose Sediment resuspension is among the most widely cited concerns that lead to restricted dredging timeframes. Protection of fish species is a primary concern regarding the effects of dredging operations, yet experimental data establishing thresholds for uncontaminated suspended sediment effects are largely lacking. We conducted research to determine suspended sediment effects on walleye ( Sander vitreus ) egg hatching success and gross morphology following exposures mimicking sediment resuspension during dredging operations. Materials and methods Newly spawned eggs of northern and southern walleye strains were continuously exposed for 3 days to suspended sediment concentrations of 0, 100, 250, and 500 mg l −1 , using sediment from Maumee Bay, OH, USA. These concentrations spanned the range measured in the vicinity of dredging operations in the Western Basin of Lake Erie. Results and discussion Northern and southern strain egg hatching rates were 53% and 39% of exposed eggs and 82% and 74% of viable eggs exposed, which are within reported ranges for this species. Data indicated no statistically significant effects of suspended sediment on hatching success. Gross morphological observations of exposed fry yielded no evidence of detrimental effects. Conclusions Experimental results indicated that walleye eggs are relatively tolerant to exposures likely to be encountered at dredging projects as performed in the Great Lakes region. Our results suggest that, given detailed knowledge of dredging project site-specific conditions and the mode of dredging to be used, better informed decisions can be made regarding adequate protective management practices. In many cases, flexibility could be given to the dredging contractor while maintaining a very low probability of risk to walleye spawning habitat.

Estimating the abundance of organisms is fundamental to the study and management of ecological systems. However, accurately and precisely estimating organism abundance is challenging, especially in aquatic systems where organisms are hidden underwater. Estimating the abundance of fish is critical for the management of fisheries which relies on accurate assessment of population status to maximize yield without overharvesting populations. Monitoring population status is particularly challenging for inland fisheries in which populations are distributed among many individual waterbodies. Environmental DNA (eDNA) may offer a cost‐effective way to rapidly estimate populations across a large number of systems if eDNA quantity correlates with the abundance of its source organisms. Here, we test the ability of quantities of eDNA recovered from surface water to estimate the abundance of walleye (Sander vitreus), a culturally and economically important sportfish, in lakes in northern Wisconsin (USA). We demonstrate a significant, positive relationship between traditional estimates of adult walleye populations (both number of individuals and biomass) and eDNA concentration (R2 = .81; n = 22). Our results highlight the utility of eDNA as a population monitoring tool that can help guide and inform inland fisheries management. Quantity of eDNA predicts abundance of an economically important sport fish (Sander vitreus) in inland lakes of northern Wisconsin (USA; R2 = .81). These results highlight the utility of eDNA as a population monitoring tool that can help guide and inform inland fisheries management.

Human-driven nutrient inputs into aquatic ecosystems must be managed to preserve biodiversity and to ensure that valued fishery and water quality services are not compromised by hypoxia and harmful algal blooms. Aiming for nutrient inputs that achieve an intermediate level of ecosystem productivity is expected to provide both high fish yield and good water quality. However, we argue that such an intermediate “optimum” may not exist for many aquatic ecosystems that support multiple fisheries with differing tolerances to eutrophication and that must provide multiple water quality services. We further support this argument with an empirical case study of nearly a century (1915–2011) of change in the productivity of Lake Erie and its lake whitefish (Coregonus clupeaformis), walleye (Sander vitreus), and yellow perch (Perca flavescens) fisheries. We discuss and show how the harvest of each fishery has been historically maximized at different levels of ecosystem productivity. Additionally, we examine how anticipated management efforts to improve water quality by reducing nutrient inputs (i.e., oligotrophication) may favor certain fisheries over others, resulting in no single optimal range of nutrient inputs that achieves all valued fishery and water quality objectives. Our synthesis and case study illustrate how the need to balance multiple services in aquatic ecosystems can create a wicked management problem with inevitable trade-offs. To navigate these trade-offs, we recommend the use of ecosystem-based management approaches, which can help decision makers identify and resolve complex trade-offs by facilitating cooperative research and communication among water quality regulators, fisheries managers, and end users.

Gill nets are a common sampling technique in inland and marine fisheries. However, gill nets are size selective and may result in bias estimates of population parameters. As such, selectivity is commonly assessed using indirect estimation techniques. Indirect estimates of gillnet selectivity have been suggested to improve estimates of important populations metrics (e.g., total annual mortality), but this assertion has not been assessed. In the current study, we simulated hypothetical populations of channel catfish Ictalurus punctatus , lake trout Salvelinus namaycush , walleye Sander vitreus , and white crappie Pomoxis annularis and sampled the populations based on published gillnet encounter and retention probabilities. Total annual mortality and von Bertalanffy parameters were then estimated using unadjusted (not “correcting” for selectivity processes) and adjusted (“correcting” for selectivity processes) age and(or) length data to evaluate the value of accounting for gillnet selectivity when estimating these metrics. Our results indicate that adjusting for retention and encounter probabilities rarely leads to improved estimates of total annual mortality, K , and L ∞ . For instance, estimates of annual mortality of lake trout based on age data adjusted for retention probability resulted in an overestimate of A by 14.4%. As such, we suggest that analysis of gillnet selectivity only be used when specific questions are being addressed (e.g., catch-at-age models) or in situation when all processes contributing to gillnet selectivity (e.g., contact probability, size-specific availability) are known.

Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron.