North Central Division Project Spotlight: Economic Evaluation of Barriers to Minimize Reservoir Sport Fish Escapement

By Madeline, C. Lewis, John C. Tyndall, Ben Dodd, and Michael J. Webber.

This project spotlight is a summary of the manuscript published in NAJFM in June 2024, courtesy of the authors. The full citation is at the bottom of the page. 

Economic evaluation of barriers to minimize reservoir sport fish escapement

Escapement of fish over or through water release structures can represent a substantial source of loss to reservoir populations. In systems reliant on stocking, escapement can have economic consequences as resources put into raising and stocking fish are wasted when fish escape into systems that are not accessible to anglers or suitable for long term survival. Physical barriers can be an effective method to minimize escapement, and barriers have been successfully installed on multiple Iowa reservoirs. However, there is a cost associated with the construction of barriers, as well as ongoing costs associated with maintenance and repairs. Despite increasing interest in the installation of barriers in Iowa, it was unknown whether the benefits of barrier installation outweighed the costs.

We developed a framework using simulation modeling and discounted cash flow techniques to quantify the costs and benefits of a barrier project on Brushy Creek Lake, Iowa, where a barrier was constructed in 2020 to reduce escapement of stocked Walleye Sander vitreus and Muskellunge Esox masquinongy. We found that the value of escaped fish quickly exceeded the cost of installing and maintaining a barrier, with a 99% probability of positive net benefits after three years. Within 5 years, the present value of Walleye and Muskellunge escapement from Brushy Creek (mean = $166,103, range = $120,207–207,656) was more than double the present value of barrier construction and maintenance (mean = $64,337, range = $60,897–$67,237), a mean net benefit of barrier construction of $101,765 ($58,300–$144,292; Figure 1). The mean benefit–cost ratio of the barrier was 4.55 after 10 years, indicating that for every present‐value $1 spent on the barrier construction, a present‐value $4.55 was saved by preventing the escapement of fish. There was a 99% probability that the net benefits of the barrier would be positive after 3 years when considering both species (Figure 2).

Figure 1. Cost (present value) of Walleye and Muskellunge escapement from Brushy Creek Lake (blue) compared with the cost of installing and maintaining a parallel‐bar barrier (green) over time. Each point denotes mean cost over 10,000 simulations, error bars denote minimum and maximum values, and the dashed line denotes the benefit–cost ratio.

Figure 2. Probability that the net benefit of the barrier will be greater than or equal to zero over time, with 10,000 simulations occurring at each time step, and line color denoting species. Dashed lines denote the time period where the probability of a positive net benefit is >99%.

We then incorporated our simulation modeling framework into a free, open-access R Shiny application (https://fishbarrier.nrem.iastate.edu/). The flexible and interactive nature of the Shiny application enables the quantification of barrier costs and benefits on a wide range of reservoir sizes, barrier types and costs, escapement rates, and fish species. Additionally, managers are often faced with the challenge of making decisions regarding a system where they may have limited knowledge regarding the system and vital rates, such as survival or escapement rates. The application enables managers to assess potential outcomes over a range of different inputs which can be used in situations where there is uncertainty regarding what the actual rates are.

Our results indicated that barriers can be a cost-effective solution to minimize escapement of reservoir sportfish. Incorporating economics into fisheries management can enable informed transparent decision making which is particularly vital in reservoir systems which often have multiple uses and stakeholders involved. The Shiny application has already been used to assist in decision making regarding future barrier construction projects in Iowa.

Brushy Creek fish barrier (photo by Ben Dodd, Iowa DNR).

Citation and Link to Manuscript

Madeline C. Lewis, John C. Tyndall, Ben Dodd, Michael J. Weber, Economic evaluation of barriers to minimize reservoir sport fish escapement, North American Journal of Fisheries Management, Volume 44, Issue 3, June 2024, Pages 677–692, https://doi.org/10.1002/nafm.11009

QR Code for barrier application.