Past Research Projects
It’s Complicated and It Depends: A Review of the Effects of Ecosystem Changes on Walleye and Yellow Perch Populations in North America
Will property values cool as EWM invasion heats up?
Eurasian watermilfoil (EWM) is an invasive aquatic macrophyte of high ecological and economic concern that has invaded lakes and waterbodies of Minnesota since late 1980’s. Often considered a nuisance species by boaters and fishing enthusiasts; large population densities of EWM is known to hinder boating activities and alter lake ecology impacting quality of recreational fishing. EWM invasion can also lower the aesthetic appeal of heavily infested lakes, which can have a tangible economic impact in the form of depreciated lake-front property values. As part of an ongoing long-term monitoring and mitigation program of aquatic invasive species (AIS) across Minnesota, our research on EWM focuses on the following goals:
Identify key ecological drivers of EWM invasion, especially the role of lake-specific water temperature and water chemistry attributes
Predict distribution and abundance of EWM invasion under current and future climates
Link and model the potential economic impact of EWM infested lakes on lake-front property values
Develop an interactive online dashboard to communicate research findings to stakeholders and lay audience
Eurasian watermilfoil distribution, abundance, and impacts
Water clarity and temperature influence walleye abundance and sustainable harvest.
Walleye prefer low water clarity and cool water temperatures. Water clarity and temperature combine to determine the amount of suitable walleye habitat in a lake, known as its thermal-optical habitat area. Work in Mille Lacs has related changes in thermal-optical habitat to walleye abundance and safe harvest. We are extending this work to other walleye lakes in Minnesota to understand how changes in temperature and clarity influence walleye across diverse lakes.
Walleye habitat status assessment to guide and prioritize management
Walleye are an important sport fish in Minnesota and are managed in over 1,400 lakes. Declining walleye populations in Midwestern lakes are a major concern, and multiple walleye lakes must be managed with limited resources. To improve walleye management are evaluating the status of walleye populations relative to their habitat potential, and the sensitivity of walleye habitat to changing water clarity and temperature.
Status: Lakes with abundant habitat generally produce the most walleye. Quantifying the status of a lake’s walleye habitat will help prioritize lakes for management based on their potential. Walleye population status relative to expectations based on habitat area can guide harvest policies – for example, regulations may be relaxed when abundance exceeds expectations, and restricted when abundance is lower than expected.
Sensitivity: Minnesota lakes are undergoing changes in water clarity and water temperature. The effect of these changes on walleye habitat will vary among lakes. Assessing the sensitivity of individual lakes to changes in water clarity and temperature will allow forward-looking management that focuses limited resources on the most resilient lakes that are least likely to be negatively affected by changing conditions.
Water clarity influences walleye safe harvest in Mille Lacs
Walleye in Mille Lacs and the safe operating space
Mille Lacs supports the most popular walleye fishery in Minnesota. Declining walleye populations over the past decade or more have resulted in highly restrictive harvest regulations and social, economic, and political turmoil. We related walleye declines to increased water clarity, and propose that decreasing safe harvest limits in response to declining habitat availability can keep this iconic ecosystem within the safe operating space of sustainable fisheries.
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Temperature is a critical driver of ecosystem processes and food web dynamics. Past water temperatures may provide insights into mechanisms behind observed trends in aquatic ecosystems, and projections of future water temperatures can help prioritize management actions. Unfortunately, very few lakes are monitored for water temperature on the spatial scale and resolution necessary for these types of research questions. Air temperatures are widely available, but lake temperatures do not track air temperatures linearly. The decoupling of air and water temperatures is especially apparent in deep waters that provide critical habitat for cool- and cold-water fishes.
Together with collaborators at the United States Geological survey and the University of Minnesota Computer Science department, we are combining mechanistic, thermodynamic models of lake temperatures with deep learning methods to accurately to hindcast and forecast water temperatures of tens of thousands of lakes in the Midwestern United States. This model generates daily, depth-specific thermal profiles for the past and future that can be linked to critical ecosystem functions such as the abundance of walleye or other fish species. To date, we have demonstrated strong connections between modeled lake temperatures and walleye recruitment in Wisconsin. Work is ongoing to improve model accuracy, and to link model outputs to ecological processes.
Climate Change and Lake Temperature
Once an invasive species establishes a self-sustaining population, few options exist for mitigating its negative effects. Eradication or control of invasive species can be successful under certain conditions, but eradication efforts can produce unexpected results , particularly when an invader has been established for long time periods, exhibits strong interactions with other species, or alters physical properties of an ecosystem.
Rusty crayfish are invasive in the upper Midwest. Rusty crayfish eliminate aquatic plant beds and negatively impact panfish and invertebrate populations. Rusty crayfish were experimentally removed from Sparkling Lake, a 64 hectare lake in Vilas County, Wisconsin, from 2001-2008 via intensive trapping and changes in sport fish regulations in an attempt to restore the lake to pre-invaded conditions. The removal was successful in reducing rusty crayfish catch rates by over 99%, and the native virile crayfish increased in abundance 100-fold over this time period. As of 2019, rusty crayfish in Sparkling lake remain at low densities, and the aquatic ecosystem has exhibited substantial changes as a result. Monitoring of Sparkling Lake pre- and post- removal was conducted by the North Temperate Lakes LTER.
Whole-lake Removal of Invasive Rusty Crayfish
Invasive species are recognized as a leading driver of environmental change. Their impacts are often linked to their population size, but surprisingly little is known about how frequently they achieve high abundances. A nearly universal pattern in ecology is that species are rare in most locations and abundant in a few, generating right-skewed abundance distributions. Together with many collaborators, we collated abundance data from over 24,000 populations of 17 invasive and 104 native aquatic species to test whether invasive species differ from native counterparts in statistical patterns of abundance across multiple sites.
Invasive species on average reached significantly higher densities than native species and exhibited significantly higher variance. However, invasive and native species did not differ in terms of CV, skewness, or kurtosis. Abundance distributions of all species were highly right skewed, meaning both invasive and native species occurred at low densities in most locations where they were present (6% and 2% of the maximum densities observed within a taxa, respectively). The biological significance of the differences between invasive and native species depends on species-specific relationships between abundance and impact. Recognition of cross-site heterogeneity in population densities brings a new dimension to invasive species management, and may help to refine optimal prevention, containment, control, and eradication strategies.
Abundance of Invasive Species
