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Research |
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During the spring of 2007, two pools of the Kanawha River were sampled for benthic fishes. Trawling was completed using a Missouri modified trawl. One two minute trawl on the right or left descending bank was taken, two two minute trawls were taken in the area between the bank and the middle of the channel and one two minute trawl was taken in the middle of the channel at each site on the Kanawha River. Sites were selected by two means. All sites within ½ mile of any lock and dam structure and over any known intake or subterranean pipeline crossing for safety were sampled. Ten sites were randomly selected from a subset of all "high quality" substrates. High quality sites were determined by utilizing substrate maps created from US Army Corps of Engineers side scan sonar data. All habitat patches were categorized by those with more than 80% gravel from those with less gravel substrate. Based on literature these high gravel sites should represent preferred benthic fish habitat. A second set of ten sites were randomly selected from all other sites that were large enough to trawl for two minutes. The initial study was to determine the effectiveness of side-scan sonar habitat maps as predictor of benthic fishes diversity and densities. While we did see a trend on increasing densities and diversity, multiple outliers were identified. The low number of high quality sites sampled would result in even a few outliers to impact the detection of a significant biological signal. One means of strengthening the study is to add additional sites. We chose forty additional sites in the next two pools of the Kanawha River. The outlier sites had much lower numbers and diversity of benthic fishes than predicted by the habitat maps. Based on-site observations, we believed these sites had a significant layer of fine sediments overtop the gravel beds. These fines would reduce dissolved oxygen, smother eggs, and reduce prey items for benthic fishes. Fine sediments would be obscured on side scan sonar until sediment depths became large enough to overcome backscatter of the sound waves. One goal of this project would be to use additional means to determine substrate composition. A second goal would be to determine the distribution of small benthic fishes in the upper most two pools of the Kanawha River. In the lower pools we found several significant species including multiple crystal darters and sand darters which had never been collected in the Kanawha River (Table 1). So through the use of more data on substrate composition we can determine if the side scanner sonar is a accurate and reliable tool in mapping high quality habitat sites for benthic fishes. We will also be able to look at the fish populations in the upper two pools of the Kanawha River and compare them to the lower pools of the Kanawha River as well as other large river ecosystems. Through our research we hope to find the best method of monitoring these benthic fish communities.
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