Wisconsin Lakes Research Articles

Hatch timing of largemouth bass: implications for recruitment at the Northern edge of their native range

Climate-related shifts in hatch timing could mean that age-0 largemouth bass Micropterus salmoides in north temperate lakes reach larger sizes and experience higher survival, which may contribute to increased prevalence of this species in many lakes. However, information on age-0 largemouth bass life history is lacking for these lakes. We estimated hatch dates, daily growth rates (DGR), and length-based probability of piscivory of age-0 largemouth bass in Wisconsin lakes to: (1) provide baseline data on early life history; (2) compare hatch timing between years with different spring temperature regimes, and (3) project how shifts in hatch timing might influence total length (TL) distributions of age-0 bass if mean DGR remained constant. Most age-0 largemouth bass (>90%) collected from ten Wisconsin lakes (N = 746) hatched between 23 May and 24 June during 2012 and 2013 and did not switch to piscivory during their first summer. Prevalence of positive correlations (16 of 24 lake-year pairings) between TL in and age indicates hatch timing may influence TLs attained by age-0 largemouth bass in August in some lake-years. Mean daily water temperatures in May 2012 were 3.1 °C warmer than in May 2013 for the five of the six lakes where hatch dates were estimated in both years. On average, earliest and median hatch dates for age-0 largemouth bass in these six lakes were 10–11 d earlier in 2012 than in 2013 and hatch duration was approximately 8 d longer in 2012. Despite differences in hatch timing, mean DGR was relatively consistent (range = 0.61–0.74 mm/d) between lakes and years. Simple simulations suggest that earlier hatch dates could result in more age-0 largemouth bass reaching TLs associated with piscivory and overwinter survival by the end of their first summer if growth rates did not change, which could translate to higher recruitment.

A Lake in Wisconsin

A Lake in Wisconsin

Preferential Partitioning of Per- and Polyfluoroalkyl Substances (PFAS) and Dissolved Organic Matter in Freshwater Surface Microlayer and Natural Foam.

Per- and polyfluoroalkyl substances (PFAS) are surfactants that can accumulate in the surface microlayer (SML) and in natural foams, with potential elevated exposure for organisms at the water surface. However, the impact of water chemistry on PFAS accumulation in these matrices in freshwater systems is unknown. We quantified 36 PFAS in water, the SML, and natural foams from 43 rivers and lakes in Wisconsin, USA, alongside measurements of pH, cations, and dissolved organic carbon (DOC). PFAS partition to foams with concentration ranging 2300-328,200 ng/L in waters with 6-139 ng/L PFAS (sum of 36 analytes), corresponding to sodium-normalized enrichment factors ranging <50 to >7000. Similar enrichment is observed for DOC (∼70). PFAS partitioning to foams increases with increasing chain length and is positively correlated with [DOC]. Modest SML enrichment is observed for PFOS (1.4) and FOSA (2.4), while negligible enrichment is observed for other PFAS and DOC due to low specific surface area and turbulent conditions that inhibit surfactant accumulation. However, DOC composition in the SML is distinct from bulk water, as assessed using high-resolution mass spectrometry. This study demonstrates that natural foams in unimpacted and impacted waters can have elevated PFAS concentrations, whereas SML accumulation in surface waters is limited.

Exposure to and Biomarker Responses From Legacy and Emerging Contaminants Along Three Drainages in the Milwaukee Estuary, Wisconsin, USA.

Legacy contaminants and contaminants of emerging concern (CECs) were assessed in tree swallow (Tachycineta bicolor) tissue and diet samples from three drainages in the Milwaukee estuary, Wisconsin, USA, to understand exposures and possible biomarker responses. Two remote Wisconsin lakes were assessed for comparative purposes. Bioaccumulative classes of contaminants, such as polybrominated diphenyl ethers and per- and polyfluoroalkyl substances, while at higher concentrations than the reference lakes, did not vary significantly among sites or among the three drainages. Polycyclic aromatic hydrocarbons were assessed in diet and sediment and were from primarily pyrogenic sources. Ten biomarkers were assessed relative to contaminant exposure. Polychlorinated biphenyls (PCBs) were elevated above reference conditions at all Milwaukee sites but did not correlate with any measured biomarker responses. Only one site, Cedarburg, just downstream from a Superfund site, had elevated PCBs compared to other sites in the Milwaukee estuary. Few non-organochlorine insecticides or herbicides were detected in tree swallow liver tissue, except for the atrazine metabolite desethylatrazine. Few pharmaceuticals and personal care products were detected in liver tissue except for N,N-diethyl-meta-toluamide, iopamidol, and two antibiotics. The present study is one of the most comprehensive assessments to date, along with the previously published Maumee River data, on the exposure and effects of a wide variety of CECs in birds. Environ Toxicol Chem 2024;43:856-877. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Mark–recapture surveys affect nest site fidelity but not reproductive timing of male Smallmouth Bass

AbstractObjectiveFish population surveys in north‐temperate lakes are often conducted in the fall or spring when individuals are easy to capture with traditional fisheries techniques. Because some fishes are preparing to spawn or are spawning during these seasons, there is a critical need to better understand the potential influences of these surveys on decisions that are related to fish reproduction.MethodsWe tested whether spring mark–recapture surveys using fyke nets followed by electrofishing affect the reproductive behaviors of male Smallmouth Bass Micropterus dolomieu in a northern Wisconsin lake. Fyke netting, electrofishing, and whole‐lake nest snorkeling surveys were conducted during 2001–2008, and Floy‐tagged males were tracked across years to test whether capture in the fyke nets only or capture in the electrofishing survey influenced interyear nest site fidelity and reproductive timing.ResultThe mark–recapture surveys were conducted preceding the spawning of Smallmouth Bass, and returning males that were caught in the electrofishing survey nested ~50 m farther from their prior year's nest than both males that were captured only in fyke nets and males that were captured by neither method. Average interyear nest distances were ~200 m, and median interyear nest distances were ~90 m for males that were not captured in the electrofishing survey. Electrofishing and fyke netting did not influence the timing of reproduction.ConclusionSpring electrofishing surveys for Smallmouth Bass have the potential to displace breeding males from preferred nesting habitats. If displacement negatively influences fitness (i.e., age‐0 survivorship to maturation), spring electrofishing surveys would not be recommended for assessing Smallmouth Bass populations. However, spring population surveys often occur soon after ice off, and surveys that are conducted at these colder temperatures are typically less stressful and less likely to result in mortality. Future research should test for fitness implications of reduced nest site fidelity following electrofishing in Smallmouth Bass while considering potential fitness trade‐offs if surveys are moved later in the year.

Response of yellow perch to water level fluctuations in oligotrophic, north‐temperate inland lakes

AbstractInformation on yellow perch Perca flavescens population dynamics and responses to various abiotic and biotic factors in oligotrophic, north‐temperate inland lakes is limited. Water level fluctuations are known to influence available habitat and biological communities within the littoral zones of lakes, yet research is lacking for yellow perch in Wisconsin. The goal of our study was to characterize yellow perch population‐level responses to natural water level fluctuations in four northern Wisconsin lakes using a 39‐year time series. On average, increasing water level periods correlated with lower mean fyke net and gill net relative abundances (catch‐per‐unit‐effort), though generally not statistically significant. Yellow perch mean relative weight varied among lakes and was significantly greater during increasing water level periods for all lakes except one. The lack of statistically significant findings potentially suggests a buffering mechanism of north‐temperate oligotrophic lakes due to their small surface area to volume ratios, relative lack of nutrients, and(or) littoral structural habitat compared to other systems (e.g., shallow eutrophic lakes). Our results suggest that natural water level fluctuations may not be an environmental concern for yellow perch populations in some north‐temperate oligotrophic inland lakes.

Cisco population characteristics in Wisconsin lakes in relation to lake‐ and landscape‐level factors

AbstractObjectiveDeclines in Cisco Coregonus artedi populations in some inland lakes have prompted assessments of Cisco occurrence and extirpation risk in relation to various stressors to identify refuge lakes and factors that promote Cisco persistence. However, most previous assessments have focused on presence–absence of Cisco rather than examining how population characteristics, such as relative abundance or growth, might change in relation to lake‐ and landscape‐level environmental factors. Consequently, our specific objectives were to identify important environmental factors explaining variation in Cisco relative abundance and growth and to determine whether population metrics describing size and age distributions were related to relative abundance in Wisconsin inland lakes.MethodsCisco were collected from 48 inland Wisconsin lakes during 2011–2015 using vertical monofilament gill nets and population‐specific relative abundance estimates (catch per unit effort [CPUE]) were quantified as the number of individuals per gill‐net night. Sagittal otoliths were removed from a subsample of Cisco for age estimation and growth was indexed as mean total length (TL; mm) at age 2. Length and age data were used to develop a suite of metrics describing size and age distributions of each population. Random forest models were used to evaluate relationships between 10 biologically relevant predictor variables representing variation in physical, climatic, catchment, and limnological characteristics and Cisco CPUE and growth. Pearson correlations were used to determine whether population characteristics were related to CPUE.ResultCisco populations exhibited large variation in relative abundance, growth, and size and age distributions. Best‐fit random forest models explained approximately 25% of the variation in Cisco CPUE and 46% of the variation in growth. Growing degree‐days and variables associated with availability, quality, and quantity of suitable oxythermal conditions were identified as important predictors of both Cisco CPUE and growth; CPUE was also identified as an important predictor of growth. Mean TL and mean TL at age 2 were negatively related to Cisco CPUE, whereas mean age, number of age‐classes present, and maximum observed age were positively related to CPUE.ConclusionOur results suggest that maintenance of suitable oxythermal habitat conditions may be critical to conserving abundant Cisco populations. Our assessment also provides insights on how Cisco populations may respond to environmental and anthropogenic stressors, which could aid ongoing and future conservation and management efforts in Wisconsin and elsewhere.

Beyond Phosphorus: Salinization as a driver of eutrophication symptoms in North American lakes

The acceleration of global urbanization continues to fuel concerns surrounding water quality impairments in urban lakes, particularly eutrophication. Eutrophication of freshwater environments is generally assumed to be driven by increased anthropogenic phosphorus (P) supplies which can alleviate limitations on primary production. Salinization is also recognized as a stressor on urban freshwater quality, particularly in cold temperate climate regions where salts are applied to road surfaces as de-icing agents. While the ecological damages caused by P enrichment and salinization to freshwaters are both well established, thus far, their impacts on water quality have only been considered independently. Although improvements to the management of urban stormwater and wastewater have decreased P inputs to freshwater systems in recent decades, many lakes worldwide remain eutrophic, as indicated by declining dissolved oxygen (DO) concentrations and rising dissolved inorganic P (DIP) concentrations in the hypolimnion. Our previous study of an urban freshwater lake in Ontario, Canada, showed that persistent eutrophication symptoms are linked to salinization associated with impervious land cover expansion, rather than increased external P loading. In this research, we present a multiple decade of water chemistry data analyses for several other urban lakes in Ontario, Wisconsin, and Minnesota to determine how increased lake salinization rates intersect with water temperature and morphometry to alter water column stratification, thus, increasing eutrophication symptoms. Our trend analysis shows progressive salinization (observed through significant increases in chloride or electrical conductivity) of all the lakes investigated. Calculations of lakes mixing indices over time show that, on average, lake stratification is becoming more stable with increased salinity playing a crucial role in enhancing lake stratification. Overall, salinity is becoming a stronger regulator of water density than temperature in the cold temperate urban freshwater lakes of North America. The increasing salinity trends are accompanied by increasing hypolimnion hypoxia and increasing DIP to total P (TP) ratios in all lakes, thereby demonstrating the mechanistic link between salinization and internal P loading. Rising salinity intensifies water column stratification, in turn, reducing the oxygenation of the hypolimnion and enhancing internal P loading from the sediments. These results highlight that stricter management of de-icing salt application rates should be considered to control lake eutrophication symptoms in cold climate regions.

Quantifying the Role of Simultaneous Transformation Pathways in the Fate of the Novel Aquatic Herbicide Florpyrauxifen-Benzyl.

Predicting the fate of organic compounds in the environment is challenging due to the inability of laboratory studies to replicate field conditions. We used the intentionally applied aquatic herbicide florpyrauxifen-benzyl (FPB) as a model compound to investigate the contribution of multiple transformation pathways to organic compound fate in lakes. FPB persisted in five Wisconsin lakes for 5-7 days with an in-lake half-life of <2 days. FPB formed four transformation products, with the bioactive product florpyrauxifen persisting up to 30 days post-treatment. Parallel laboratory experiments showed that FPB degrades to florpyrauxifen via base-promoted hydrolysis. Hydroxy-FPB and hydroxy-florpyrauxifen were identified as biodegradation products, while dechloro-FPB was identified as a photoproduct. Material balance calculations using both laboratory rates and field product concentrations demonstrated that hydrolysis (∼47% of loss), biodegradation (∼20%), sorption (∼13%), and photodegradation (∼4%) occurred on similar timescales. Furthermore, the combined results demonstrated that abiotic and plant-catalyzed hydrolysis of FPB to florpyrauxifen, followed by biodegradation of florpyrauxifen to hydroxy-florpyrauxifen, was the dominant transformation pathway in lakes. This study demonstrates how combined field and laboratory studies can be used to elucidate the role of simultaneous and interacting pathways in the fate of organic compounds in aquatic environments.

Lakeshore residential development as a driver of aquatic habitat and littoral fish communities: A cross-system study.

Lakeshore riparian habitats have undergone intensive residential development in many parts of the world. Lakeshore residential development (LRD) is associated with aquatic habitat loss/alteration, including altered macrophyte communities and reduced coarse woody habitat. Yet habitat-mediated and other generalized effects of LRD on lake biotic communities are not well understood. We used two approaches to examine the relationships among LRD, habitat, and fish community in a set of 57 northern Wisconsin lakes. First, we examined how LRD affected aquatic habitat using mixed linear effects models. Second, we evaluated how LRD affected fish abundance and community structure at both whole-lake and site-level spatial scales using generalized linear mixed-effects models. We found that LRD did not have a significant relationship with the total abundance (all species combined) of fish at either scale. However, there were significant species-specific responses to LRD at the whole-lake scale. Species abundances varied across the LRD gradient, with bluegill (Lepomis macrochirus) and mimic shiners (Notropis volucellus) responding positively along the gradient and walleye (Sander vitreus) having the most negative response. We also quantified site-level habitat associations for each fish species. We found that habitat associations did not inform a species' overall response to LRD, as illustrated by species with similar responses to LRD having vastly different habitat associations. Finally, even with the inclusion of littoral habitat information in models, LRD still had significant effects on species abundances, reflecting a role of LRD in shaping littoral fish communities independent of our measure of littoral habitat alteration. Our results indicated that LRD altered littoral fish communities at the whole-lake scale through both habitat and non-habitat-mediated drivers.

Evaluation of survival and cost to harvestable age of stocked fall fingerling walleye (Sander vitreus) in Northern Wisconsin Lakes

Walleye Sander vitreus are culturally and recreationally important in Wisconsin, USA and have experienced population declines in some lakes due to reduced natural recruitment. In 2013, the Wisconsin legislature implemented the Wisconsin Walleye Stocking Initiative, a statewide rehabilitation effort to help declining walleye populations through increased stockings of fall fingerling walleye (150–250 mm). Our objectives were to: (1) test for differences in natural mortality (M) of stocked walleye among stocking densities (12.4, 24.7, 37.1 fish/ha), lake recruitment status (some natural recruitment or no natural recruitment), and lake conductivity (surrogate for lake productivity); (2) estimate cost to harvestable age (i.e., age-4); and (3) compare predicted adult walleye abundance among lakes across various stocking densities in relation to Wisconsin walleye adult abundance standards (i.e., naturally reproducing population ≥7.4 adults/ha, “fishable” population ≥ 3.7 adults/ha). Fall fingerling stocked walleye M was lowest in lakes with some natural recruitment, with medium-low and high conductivities, and stocked at 24.7 and 37.1 fish/ha, respectively. Using a mixed-effects model, fall fingerling M was negatively related to stocking density but not lake recruitment status or conductivity. No conditions resulted in the naturally reproducing population density standard to be met after multiple stockings. Two to four stocking events were required to achieve the “fishable” population standard, depending on lake conditions. When estimating cost to harvestable age, lakes stocked at 24.7 fish/ha generally had the best survival resulting in the lowest cost to age-4 ($17.70 - $35.41/fish). Lakes stocked at 12.4 fish/ha had the highest cost to age-4 ($91.17 - $182.34/fish). Juvenile walleye survival from age-0 to age-1 was dependent on lake conductivity and recruitment status, with lakes stocked at 24.7 fish/ha providing the lowest cost to age-4. Our results may inform science-based decision making and best-case scenario stocking rates to increase the probability of reestablishing walleye natural recruitment.

Seasonal habitat use of yellow perch Perca flavescens in a north‐temperate lake

AbstractKnowledge of species‐specific fish biology, ecology, and habitat use is critical for informing science‐based management. Yellow perch Perca flavescens are an ecologically and recreationally important fish species. Yet, for many north‐temperate systems (e.g. inland lakes of Wisconsin), little is known about yellow perch seasonal habitat use and ecology. We characterised yellow perch seasonal spatial distribution, size–structure, and condition between littoral and pelagic habitats in Crystal Lake (Vilas Co., WI) during the open water period of 2021. Seasonal spatial distribution and population size–structure were characterised by contemporaneous sampling in littoral and pelagic habitats using mini‐fyke nets and vertical gill nets, respectively. Relative abundance estimates for yellow perch in the littoral zone were greatest during early spring and declined throughout the open water season. Yellow perch pelagic relative abundance estimates were lowest in spring, peaked at the onset of stratification, and then declined and remained relatively consistent throughout the open water season. In general, yellow perch population size–structure and condition were greatest in the pelagic zone. Our findings suggest that after spring spawning, larger yellow perch prefer/select pelagic habitats, while sub‐adults and juveniles prefer/select littoral habitats, potentially resulting from increased predator refugia and(or) resource availability. Our results emphasise the importance of evaluating gear and fishery assessment bias, particularly when the target species may use a range of habitat types within a system.

The Finding and Description of A Diverse Population of the Southern Cestode Isoglaridacris agminis Williams and Rogers, 1972 (Caryophyllaidae) from Lake Chub Sucker Erimyzon sucetta (Lacépède, 1802) in a Northern Land-Locked Lake in Wisconsin, with a Special Reference to its Disjunct Post-Glacial Distribution in North America

Specimens of Isoglaridacris agminis Williams and Rogers, 1972 (Caryophyllidae) were first described from the lake chubsucker Erimyzon sucetta (Lacépède, 1802) in a small tributary of the Tallapoosa River at NE central Alabama. We have collected and examined I. agminis from the same host species in the land-locked Silver Lake, SE Wisconsin. We update our first and only 1986 account of this Wisconsin population, with new observations and measurements, and compare with those in the original and other descriptions. The morphology of I. agminis is revisited using light microscopy revealing new features. Emphasis is placed on the morphological variability of its unusual scolex and reproductive structures with variable ovarian shapes throughout development using many microscopic images. Measurements of 17 specimens and the re-examination of 15 more specimens from Silver Lake provided an opportunity to review the taxonomy and description of the species, distinguish locality differences, and correct and update other statements and concepts by other observers. The disconnected distribution of worms from the same host species in separate waters of various states is attributed to the disjunct post-glacial distribution of their primary hosts.

Towards quantifying microbial dispersal in the environment.

Towards quantifying microbial dispersal in the environment.

Modflow-setup: Robust automation of groundwater model construction

In an age of both big data and increasing strain on water resources, sound management decisions often rely on numerical models. Numerical models provide a physics-based framework for assimilating and making sense of information that by itself only provides a limited description of the hydrologic system. Often, numerical models are the best option for quantifying even intuitively obvious connections between human activities and water resource impacts. However, despite many recent advances in model data assimilation and uncertainty quantification, the process of constructing numerical models remains laborious, expensive, and opaque, often precluding their use in decision making. Modflow-setup aims to provide rapid and consistent construction of MODFLOW groundwater models through robust and repeatable automation. Common model construction tasks are distilled in an open-source, online code base that is tested and extensible through collaborative version control. Input to Modflow-setup consists of a single configuration file that summarizes the workflow for building a model, including source data, construction options, and output packages. Source data providing model structure and parameter information including shapefiles, rasters, NetCDF files, tables, and other (geolocated) sources to MODFLOW models are read in and mapped to the model discretization, using Flopy and other general open-source scientific Python libraries. In a few minutes, an external array-based MODFLOW model amenable to parameter estimation and uncertainty quantification is produced. This paper describes the core functionality of Modflow-setup, including a worked example of a MODFLOW 6 model for evaluating pumping impacts to a lake in central Wisconsin, United States.

Microplastic accumulation in the gastrointestinal tracts of nestling and adult migratory birds.

This study examines the abundance and types of microplastic (MP) content in the digestive system of different bird species to help us better understand MP transfer to birds from their environments. The lower GI tracts of six bird species (Tree Swallow (Tachycineta bicolor), Ovenbird (Seiurus aurocapilla), Dark-eyed Junco (Junco hyemalis), Hermit Thrush (Catharus guttatus), Tennessee Warbler (Leiothlypis peregrine), White-throated Sparrow (Zonotrichia albicollis)) were collected for MP analysis. Tree Swallows were collected from nine locations along three drainages in the Milwaukee area and at a remote lake in Wisconsin, USA and consisted of nestlings not yet fledged. The five other bird species were adult migratory bird fatalities from window strikes at the Loyola University Chicago's Lake Shore Campus. Results of plastic analysis showed that the lower GI tracts of all bird species contained different types of MPs (i.e., fibers, fragment, beads). Fiber was the most dominant, followed by fragment and beads. Microplastics were polyethylene, polyethylene terephthalate, nylon, and polyvinyl base materials. There was no statistically significant difference in the site average MP concentration for nestling Tree Swallows or in the species average concentration for adult migratory birds. However, except for Ovenbird, species of adult migratory birds had a species average MP concentration (20.1) that was statistically higher than the site-average MP concentration for Tree Swallow nestlings (5.9). The presence of MPs in the lower GI tracts of unfledged swallows could suggest that MPs had been transferred to the birds from the environment via their diet, such as flying insects-the food source of the birds. Further study should be conducted to investigate the potential transfer of MPs from aquatic insects to birds.

Black Crappie Influences on Walleye Natural Recruitment in Northern Wisconsin Lakes

AbstractWalleye Sander vitreus natural recruitment has declined in northern Wisconsin lakes over time. Several factors have been implicated to explain Walleye natural recruitment declines in Wisconsin, including climate change, Largemouth Bass Micropterus salmoides interactions, less desirable fish communities, production overharvest, and depensatory effects on recruit survival. Previous research in other systems has suggested that White Crappie Pomoxis annularis negatively influence Walleye recruitment, but interactions between Walleye recruitment and Black Crappie Pomoxis nigromaculatus have not been examined. We evaluated trends between Black Crappie and age‐0 Walleye relative abundance (catch per effort [CPE]) collected in northern Wisconsin during 1991–2017. Specifically, we tested for (1) trends in age‐0 Walleye and Black Crappie CPE over time, (2) a relationship between age‐0 Walleye and Black Crappie CPE, and (3) the influence of several abiotic and biotic covariates (including Black Crappie CPE) on age‐0 Walleye recruitment. Age‐0 Walleye CPE declined and Black Crappie CPE increased significantly during 1991–2017. Within lakes, the relationship between age‐0 Walleye and Black Crappie CPE showed a threshold effect such that age‐0 Walleye CPE was always low when Black Crappie CPE was high. Of the abiotic and biotic covariates tested to explain variability in the age‐0 Walleye and Black Crappie CPE relationship, only Black Crappie CPE was significant. Our results suggest that Black Crappie may negatively influence Walleye natural recruitment; however, we caution that our findings only reveal a pattern and not a mechanistic explanation for negative interactions between the species. Additional research is needed to test for mechanistic interactions between Walleye and Black Crappie and to inform comanagement of these species.

Structural Habitat in Lakes and Reservoirs: Physical and Biological Considerations for Implementation

AbstractIn response to declines in coarse woody habitat (CWH) and fish productivity in natural lakes and reservoirs, agencies and stakeholders have used woody and artificial habitat enhancements to slow or reverse the effects of habitat loss from aging or shoreline development. Given that natural lakes and reservoirs differ in physical and biological conditions that could influence habitat enhancement outcomes, a framework is needed to guide management expectations for CWH replacement under different ecosystem contexts. We review ecosystem contexts that influence the effects of structural habitat enhancements in natural lakes and reservoirs, use preliminary results from case studies in a natural lake in Wisconsin and two reservoirs in Illinois to illustrate the importance of these contexts, and provide management recommendations for habitat deployments that consider physical and biological ecosystem characteristics. Because of their influence on trophic transfer efficiency, trophic status and turbidity are important contexts for habitat enhancements in natural lakes and reservoirs. Habitat enhancements to large reservoirs must also contend with high nutrient loading, water level fluctuations, and longitudinal gradients in physical and biological conditions. Preliminary results from the Wisconsin experiment illustrated the importance of the recipient fish community, with rates of response to the structural enhancement varying among fish species. The Illinois case studies demonstrated how the magnitude of change (i.e., effect size) after habitat enhancement can differ (1) between CWH additions to an oligotrophic natural lake and a eutrophic, turbid reservoir and (2) by longitudinal position of artificial habitat within a large reservoir. The functions or ecosystem services of CWH targeted for rehabilitation provide guidance as to which ecosystem features will shape the strength, direction, and duration of response. Future whole‐ecosystem manipulations are needed across a wider range of environmental contexts and fish productivity responses, and the strength of productivity increases should be compared to increased harvest efficiency.

Density‐dependent and environmental influences on juvenile walleye Sander vitreus (Mitchill) survivorship in northern Wisconsin lakes

Walleye, Sander vitreus (Mitchill), natural recruitment has declined in northern Wisconsin lakes over time. Age-0 and age-1 walleye relative abundance (catch per unit effort; CPE) data from northern Wisconsin (1986–2019) were used to test for abiotic (i.e. lake characteristics and temperature variables) and biotic (age-0 and age-1 CPE) factors influencing age-0 to age-1 walleye mortality. Age-0 to age-1 walleye mortality was elevated at high age-0 CPE and variable at low age-0 CPE, which indicated strong density-dependence. Environmental factors such as spawning and ontogenetic phenology (climate change and ice-off dates), trophic mismatches, and metabolic and consumptive demand influenced age-0 to age-1 walleye mortality less strongly. Elevated age-0 to age-1 walleye mortality at low age-0 CPE supports previous findings of depensatory recruitment dynamics in northern Wisconsin walleye populations. Additional research is needed to address elevated juvenile walleye mortality at low adult stock sizes and/or with declining natural recruitment to inform management decisions.

Variability of summer cyanobacteria abundance: can season-ahead forecasts improve beach management?

Beal MRW, O’Reilly BE, Soley CK, Hietpas KR, Block PJ. 2022. Variability of summer cyanobacteria abundance: can season-ahead forecasts improve beach management? Lake Reserv Manage. 39:37–52. As anthropogenic eutrophication and the associated increase of cyanobacteria continue to plague inland waterbodies, local officials are seeking novel methods to proactively manage water resources. Cyanobacteria are of particular concern to health officials due to their ability to produce dangerous hepatotoxins and neurotoxins, which can threaten waterbodies for recreational and drinking-water purposes. Presently, however, there is no cyanobacteria outlook that can provide advance warning of a potential threat at the seasonal time scale. In this study, a statistical model is developed utilizing local and global scale season-ahead hydroclimatic predictors to evaluate the potential for informative cyanobacteria biomass and associated beach closure forecasts across the June–August season for a eutrophic lake in Wisconsin (United States). This model is developed as part of a subseasonal to seasonal cyanobacteria forecasting system to optimize lake management across the peak cyanobacteria season. Model skill is significant in comparison to June–August cyanobacteria observations (Pearson correlation coefficient = 0.62, Heidke skill score = 0.38). The modeling framework proposed here demonstrates encouraging prediction skill and offers the possibility of advanced beach management applications.