Effects of Fathead Minnows on Ecological Characteristics of Restored and Nondrained Prairie Wetlands: A Pre-treatment Summary
by
Mark A. Hanson
Kyle D. Zimmer1
Abstract
Extensive draining of prairie wetlands reduced or eliminated many functions of native prairie landscapes. Prairie wetlands provide critical habitat for numerous birds, amphibians, aquatic invertebrates, and hydrophytes throughout the northern prairie region of the U.S. Major land management goals throughout the region stem from desire to preserve and restore unique ecological functions of wetlands in this prairie landscape. Yet, functional assessment of natural and restored wetlands throughout the Prairie Pothole Region (PPR) are rare, thus wetland management activities often proceed with only limited of biological data.
Landscape-scale changes and some human uses have potential to diminish ecological integrity of natural and restored prairie wetlands and may limit biological success of restoration efforts. Drainage and conversion of prairie wetlands dramatically increased proportions of permanently-flooded aquatic habitats throughout prairie regions of Minnesota. Historically, wetland restoration programs targeted primarily permanently-flooded areas and thus contributed little to conservation of native communities of invertebrates and amphibians reliant upon seasonally-flooded wetland areas. Concurrent with this shift in wetland types (seasonals to semipermanents) there is high demand for deep prairie wetlands to be used as fish rearing areas. Though concerns are frequently raised by wetland managers over ecological consequences of fish rearing in wetlands, very little biological information is available to guide management decisions. Species interactions are key factors structuring aquatic communities, including those in prairie wetlands. A general understanding of ecological interactions involving fish will be useful in the design of future restoration strategies and will promote development of ecologically-based management practices for both nondrained and restored wetlands.
Here, we present results from the first three years of a five-year study evaluating: 1) effects of dense fathead minnow populations on ecological characteristics of restored and nondrained prairie wetlands, and 2) extent to which these fish influence reestablishment of natural communities and functions in restored wetlands, and 3) biological success of wetland restoration. Our study is based on four wetland-treatment groups: nondrained sites without fish, nondrained sites with fathead minnows, restored sites without fish, and restored sites with fathead minnows. We tested for effects of fish (presence or absence of fathead minnows), wetland history (restored or nondrained), and fish-history interactions on several ecological characteristics of study wetlands. Our wetland response variables were: 1) abundance of aquatic invertebrates, 2) abundance of selected amphibians, 3) abundance of submerged macrophytes, 4) concentrations of major water-column nutrients and chlorophyll a, and 5) water turbidity. On 8-9 October, study wetlands were treated with rotenone to remove all fish. With data collected during 1999-2000, this will facilitate "before and after" (with and without fathead minnows) comparisons and it should allow us to more accurately measure effects of these fish and responses to fish removal from our study wetlands.
Our pre-treatment results indicate that dense populations of fathead minnows influence biotic and abiotic characteristics of prairie wetlands. Wetlands with fathead minnows usually had fewer aquatic insects and important crustaceans such as large cladocera. Wetlands with fathead minnows consistently contained fewer larval tiger salamanders; likewise, adult tiger salamanders and larval leopard frogs were often less abundant in sites with fathead minnows. We were unable to relate presence of fathead minnows to abundance of submerged aquatic plants. Finally, fathead minnows were consistently associated with higher concentrations of chlorophyll a, total phosphorus, and water turbidity, probably reflecting impoverished water quality. Wetland history (nondrained vs. restored) occasionally influenced wetland characteristics, but to a lesser extent. For example, larval tiger salamanders were less abundant in restored sites during 1997, but this was not evident in 1996 or 1998. Higher concentrations of water-column total phosphorus were evident in restored wetlands with fish in 1996, but generally levels of water column nutrients, turbidity, and phytoplankton biomass (chlorophyll a) were similar between natural and restored sites. We have observed few interactions between fathead minnow presence and wetland history; this probably indicates that in most cases natural and restored sites respond similarly to influences of these fish.
Table of Contents
- Introduction
- Methods
- Results
- Discussion
- Conclusions
- Literature Cited
- Tables
- Figures
1Department of Zoology, North Dakota State University, Fargo, ND 58105
