Quantifying Littoral Zone Substrate Distribution and Coarse Woody Habitat Abundance using Low-Cost Side-Scan Sonar
Koeller, Christine A.
University of Wisconsin-Stevens Point, College of Natural Resources
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Lake-habitat features such as substrate, coarse woody habitat (CWH), depth, and vegetation are important components of the ecosystem, and are used by fish and other aquatic organisms for foraging, refuge, and spawning. Traditionally, habitat has been measured manually using quadrats and transects. Depth maps for the study area were constructed without GPS/Sonar technology. Side-scan sonar technology has more recently been used to map underwater habitat features such as substrate and coarse woody habitat; however, this technology has not been employed for habitat mapping of inland Wisconsin lakes. Our main objectives were to determine the accuracy of sonar interpretation for in-lake habitat mapping for nine Eastern Marathon County kettle lakes with glacial origin, to determine the accuracy of new depth maps created from sonar depth readings, and to determine if different habitat combinations can be used to predict fish diversity. The Lowrance® HDS5 side-scan (or structure scan) was used to collect data from nine lakes in the study area, around the entire lake perimeter starting at the shoreline, in a swath 30.5 meters wide. This data was compared to ground truth data collected from random sampling points within each habitat type using an error matrix. Results of substrate interpretation accuracy was 53 percent; whereas, CWH abundance/absence interpretation accuracy was 74 percent. This method could provide a quick, economic alternative over manual estimation for fish biologists to use when measuring in-lake habitat for future projects.