Reservoir Research Team

Harvest regulations are commonly used to manage fish populations and achieve specific fishery goals set by managers and stakeholders. Such regulations are most often used to manage sport fish populations, such as black bass, walleye, and muskellunge, but may also be used to protect commercial fisheries (e.g., channel catfish).

Management goals often differ by lake and species, with some populations managed to achieve large, trophy-sized fish, some to achieve a high catch rate by anglers, and others for biological control of forage species. Regardless of management objectives, harvest regulations are an invaluable tool to help managers achieve population-specific goals, provide quality fishing for anglers and stakeholders, and ultimately protect fish populations and ensure their viability in the future.

The Iowa DNR recently adopted a new database system for fisheries managers based around a statistical program called R Studio. With the transition to this new system, fisheries managers will be able to complete analyses in a more streamlined way. Without a regulation simulation program compatible with R Studio, however, assessments of potential management options cannot be integrated into the new system. By developing a simulation program specifically for R Studio, we aim to fill this gap and provide our fisheries managers a tool that fits seamlessly into their existing database system and helps facilitate data-driven decisions.

This study will allow fisheries managers to easily calculate population dynamics and simulate harvest regulations for individual fish populations, facilitating more responsive, science-based decisions about fishery management. Recently, Iowa DNR established greater flexibility for fishery managers to adjust harvest regulations at specific waterbodies. This study will provide a useful analytical tool for fisheries managers to justify changes.

By programming the software in R Studio, our analysis tool will not only be usable for Iowa DNR staff, but also be publicly available, allowing for a wide range of fisheries professionals to benefit from the study’s output.  Iowa DNR recently converted to Cloud-based standard data storage. This study’s product will be designed to use standard datasets already being collected by fisheries managers, minimizing extra data manipulation and custom programming by individual fishery managers. This makes evaluation of harvest regulations more efficient and standardized in methodology across the state, contributing to defensible, responsive decision-making.

The Iowa DNR has been restoring lakes using a watershed approach since the early 1990s, starting with Lake Ahquabi. The program’s impact increased when Iowa’s legislature approved $8.6 million in yearly funding in 2006. Restored lakes in Iowa usually have strong public support and benefit from increased recreational use. Unfortunately, the new lake effect can wear off quickly as fish populations stabilize, and aquatic vegetation control issues start taking more time and money to manage.

This project was started in 2014 to study which lake restoration factors, planned and unplanned, lead to the fastest fishery recovery and popularity with anglers, as well as which fishery management strategies work best. Creating or improving habitat, new fish stocking strategies, and adding public access or recreational facilities must be evaluated. For example, although constructed in-lake habitat helps to group fish for anglers, which type of structure is most often used for fishing has not been identified. This information would let managers install the type of structures that anglers use the most.

The Iowa DNR uses angler surveys to measure the success of constructed habitat and other pieces of lake restoration. These on-lake surveys can help determine fishing success, angler satisfaction, recreational use and economic impact before and after a restoration. Angler surveys are being done at Easter Lake (major renovations began in 2015), Green Valley Lake (restored in 2009), Twelve Mile Lake (restored in 2006), Three Mile Lake (fishery renovated in 2016), Hickory Grove Lake (scheduled for future restoration), and Thomas Mitchell Pond (dredged in 2011).

As the Lake Restoration program grows and continues to invest in Iowa’s lakes and reservoirs, the method to prioritize and select lakes becomes very important. The first list of program priority lakes was based on potential for public benefit, ecological health, and overall project feasibility. These categories are important, but several new or greatly expanded datasets are available that were not before. These datasets include the Iowa Lakes Information System, Iowa Lakes Survey, and improved geographic information from high-resolution photography (LiDAR) and detailed lake mapping. A decision-making model that incorporates data on ecological health (measured by water quality, biological integrity, and habitat quality), potential for public benefit, and project feasibility is being developed.

Walleye fisheries are mainly sustained in Iowa’s reservoirs through stocking, rather than natural reproduction. Unfortunately, even intensive stocking of high numbers of fish can fail due to weather and water conditions at the time of stocking, competition with other young fish, high overwintering deaths, and lots fish escaping over the dam and downstream. Low survival of stocked fry and fingerling-sized Walleye can be a major barrier to maintain the adult densities that fisheries management biologists target.

The success of fish stocked may depend on physical and behavioral characteristics unique to the genetic strain. Lake-strain Walleye, adapted to lake and reservoir life, and river-strain Walleye, adapted to moving waters, may perform differently in different environmental conditions. A study, started in 2019, compares the two strains when stocked into reservoirs with varying physical and environmental characteristics. The first year was dedicated to careful study design, with many reservoirs across the state examined for their fit as a Walleye stocking location. A laboratory method for identifying genetic strain from tissue samples was also developed. Subsequent years will involve stocking Walleye fry of both genetic strains, followed by field sampling to determine survival and growth over time.

If Walleye strains differ in long-term survival and recruitment to the fishable stock, then strain choice becomes an important factor in stocking requests for lakes and reservoirs. Guidance about optimal strain choice will be developed, with clear indication of when specific stocking choices are untenable. This guidance will be provided in formal stocking recommendations designed to maximize the effectiveness of Walleye stocking in inland waterbodies. This reduces hatchery production costs while maximizing the availability of Walleye fishing opportunities across Iowa, providing the most preferred fishing opportunity to as many people as possible for as little cost as possible.

Dams are substantial barriers to fish movement in both directions, and most dams in Iowa have no fish passage infrastructure (e.g., fish ladders) to help fish move upstream. Large dams impounding major rivers, such as Red Rock Dam and Saylorville Dam, prevent most upstream movement with a sheer drop of up to forty feet. Shorter dams, like Ottumwa Hydropower Dam, may allow passage upstream during high flows. The true extent of fish movement upstream and downstream by sport fishes is unknown, and the potential for death caused by dam passage or passage through hydropower facilities is unknown.

A new hydropower facility will be working soon (estimated 2020) at Red Rock Dam, and additional hydropower facilities are possible at other locations across the state. A substantial change from hydropower facilities is the deviation of some flow into large turbines to produce power. Fish movement out of Red Rock Reservoir may then happen through the dam’s regular operations, flood operations, or the power plant. Turbine passage has been shown to cause physical damage and disorientation of fish passing through, resulting in increased deaths. Determining the potential effect of dam and turbine passage on sport fish species, especially larger-bodied fish, is important to understand the relative impact of hydropower development on fishery management.

At a broader level, large-scale fish movement in the Des Moines River is not well-studied. Tracking fish movement from the upper river downstream can help quantify the risk of fish encountering each dam and passing through various habitat types.

The information gathered from this study will help fisheries managers determine the current and potential impacts on their reservoir sport fisheries of hydropower development and of large dams in general. Fish escaping is a common and challenging issue faced by most fisheries managers, and a better understanding of conditions with high escapement can help them take mitigative actions (e.g., recovering fish in the tailwater at targeted times of the year) or adjust their fishery development tactics (e.g., stocking plans). Most importantly, the Department as a whole will be able to provide more scientific input about dam and hydropower facilities proposed in the future.

Tailwaters are the areas immediately downstream of dams affected by dam outflow. Tailwater fisheries provide high-quality fishing opportunities below large reservoirs including Lake Red Rock and Saylorville Lake. Lake Red Rock supports Walleye, White Bass, and catfish fisheries in its tailwater and is the largest upstream barrier to Shovelnose Sturgeon in the Des Moines River.

Environmental conditions related to water flow and quality sometimes lead to fish kills. Previous fish kills in the lower Des Moines, including a significant sturgeon kill in 2012, were caused by rapid reductions in reservoir water levels, high dissolved gases, high tailwater temperatures, and low flow rates downstream. Nonetheless, fish kills have occurred during high flows as well, and more information is needed to identify water level scenarios and tailwater conditions that contribute to large-scale fish mortality downstream.

This ongoing assessment is designed to monitor environmental conditions and help identify situations with high risk of causing fish death downstream. Evaluation of fish kills would help identify specific environmental conditions that create higher risk for fish death, and water level management can be adjusted to reduce that risk. Improved tailwater management can support a healthier fishery with fewer large-scale losses of sport fish and forage species. Some tailwater fisheries, such as Walleye, are also greatly dependent on stocking, and reduction of fish kills directly supports a long-lived hatchery product. Recommendations for water level management can be applied not only to current reservoir projects, but to future additions such as new hydropower facilities. The assessment was started in 2019, but will require ongoing, annual monitoring.

• Management of Sport Fisheries In Urban Lakes
• Pond Production of Fingerling Hybrid Striped Bass for Stocking into Iowa Impoundments Summary
• Rathbun Lake Habitat Assessment Summary
• Recruitment and Angler Exploitation of the Walleye Fishery at Rathbun Lake
• Evaluation of Iowa’s Standard Fisheries Sampling Program: Modified Fyke Nets (Summary)
• Evaluation of Iowa’s Standard Fisheries Sampling Program: Modified Fyke Nets (Full Report)
• An Evaluation of Walleye Stocking strategies in Tributary Reservoirs (Full Report)
• An Evaluation of Walleye Stocking strategies in Tributary Reservoirs (Summary)
• Community Fishing Survey (Full Report)
• Community Fishing Survey (Summary)
• Evaluation of Hybrid Striped Bass Introductions in Iowa (Full Report)
• Evaluation of Hybrid Striped Bass Introductions in Iowa (Summary)