My primary focus for this summer has been research on macrophyte cover in the Upper Henry’s Fork of the Snake River. My project compares fish habitat and macrophyte growth among 2 sites on the Henry’s Fork River as well as a control site on the Buffalo River as a part of the broader upper river project. Macrophytes are an essential component of fish habitat; they increase water depth while simultaneously slowing the velocity of the water thus creating optimal conditions for trout.
An example of the macrophytes from Last Chance.
There have been reports of a decline in angler satisfaction as well as anecdotal evidence of a decline in the quality of the fishery by the Flat Rock Club. If we were to gain a better understanding of this particular section of the river, the Mack’s Inn sewage treatment plant could be more effectively managed to benefit the fish populations here. My supervisor, Jack McLaren, is conducting his doctoral research on this section of the river; however, we know very little about this area. In order to help him obtain some basic background knowledge of this region, I have been tasked with looking into fish habitat variances amongst different river reaches in the Henry’s Fork watershed. I have been comparing geomorphological and qualitative habitat measurements as well as macrophyte cover amongst 3 study sites. The 3 sites that I have selected are at Last Chance, the Flat Rock Road, and the Buffalo River. Last Chance holds a large, quality population of trout while the Flat Rock Road reach holds a small fish population. The Buffalo River is a very natural, undisturbed spring-fed river so was selected as a reference site. Based on the anecdotal evidence of Last Chance being a world-class fishery and the Flat Rock Road reach holding few fish, I expect that we will discover significant variances amongst the 3 study sites. I’m predicting that substrate will be the main difference between the sites and that Last Chance will have the largest percent of macrophyte cover.
At each study site, I performed a quick site analysis to gain a qualitative understanding of each site. The platform I decided to use was the Ohio EPA’s QHEI. QHEI stands for qualitative habitat evaluation index. Many state agencies have used this particular platform to create their own habitat evaluation platforms; Idaho uses the BURP (beneficial use reconnaissance platform). This particular platform uses electrofishing as a part of the evaluation; however, I did not have the resources to electro fish the river. The QHEI is one of the more thorough platforms used so Jack McLaren and I thought it would be the best platform to use. The QHEI scores for each site were all very similar. The Flat Rock reach scored a 65, Last Chance a 68, and the Buffalo River a 73.5. The primary differences for each site were substrate. Last Chance consisted primarily of boulders and cobble whereas the Flat Rock reach was made up of mostly gravel and sand. Both reaches where fairly confined, meaning that they had very little interaction with the riparian zone and flood plains.
An example of the substrate at Last Chance.
An example of the substrate at the Flat Rock reach.
The Buffalo River on the other hand had lots of interaction with its riparian zone and flood plains. It also had a large variety of substrate ranging all the way from boulders to silt and muck. The Buffalo River scored a 73.5. Based on the QHEI report, we would expect the best fishery to be found in the Buffalo River; however, we know this to not be true.
An example of the substrate at the Buffalo River.
While the QHEI is a great way to gain a qualitative understanding of a river, it has no statistical power. The QHEI is essentially an educated guess at what the river habitat is like. On the other hand, the macrophyte cover estimates that I use in this study do have statistical significance and are much more exact. In order to ensure that the sample population is as representative of the actual macrophyte population as possible, I calculated that 30 random locations per sample site would provide the most robust results. 30 random locations were generated for each sample site scattered over an area of 31,000 square meters. A wooden box with a plexiglass bottom was used for viewing macrophyte cover and estimating percent cover. By obtaining quantitative data, we will be able to effectively compare it to the qualitative data obtained via the QHEI thus comparing the two methodologies. This portion of the study is currently ongoing.
A macrophyte percent cover estimate at the Flat Rock reach. This one was estimated at 45% cover.
My last sampling date is set for this coming Friday so I will share my findings in my next blog post next week!