Nicholas Davis and Dr. Ryan Jensen, Department of Geography

Global bio-diversity is being threatened by many different factors. Most of this is man induced. One of these factors is the introduction of non-native organisms to new locations. One hypothesis that explains why some non-native invasive organisms are so successful is that the native organisms have not evolved strategies to effectively interact with the new organism’s strategy (e.g. competition, predation impacts). Essentially, they are unprepared to defend themselves or deal with the novel threat.

A non-native fish predator is threatening many populations of the varied native fish species of Utah (Belk and Johnson 2007). This predator is Salmo trutta, commonly known as the brown trout. Brown trout have been shown to negatively impact native fish survival both through displacement and direct predation (Olsen and Belk 2005, McDowall 2006). Brown trout are largely piscivorous, meaning that they tend to feed on other fish.

The effectiveness of fish predators in catching prey can be influenced by many factors. It has been shown in laboratory settings that increasing turbidity can drastically decrease the predation rates of piscivors and affect prey selection (Carter 2010). With this study we aimed to test whether or not turbidity has an affect on the stream fish community dynamics where brown trout and native fish coexist. We hypothesized, based on previous observations and studies, brown trout numbers would decrease in higher turbidity levels and that native fish populations would increase. The purpose of this was to be able to predict possible native fish refuge or restoration areas based on turbidity levels.

To collect the data for this study we both had to head into the field and collaborate with Utah government agencies to obtain data from their fieldwork. The process began by contacting Utah Department of Wildlife Resources (UDWR) regional fisheries biologists, telling them about the project, and requesting the fish population data from their stream electrofishing surveys. Government biologists are very busy people, so we decided to ask just for the location coordinates of their sites so that we could go out and measure turbidity there.

We began sampling late summer 2010 because that is when streams generally are at their lowest flows, lowest turbidity, and highest fish activity. Turbidity at this time would have its greatest effects of the year. Our stream sampling lasted from August to early November. While traveling and doing the fieldwork we ran into a couple of problems. First of all, several of the sites where the DWR sample, are located on private property or are very difficult to access due to extremely rugged terrain. Second, we were unable to locate many of the sites due to unfamiliarity and inaccurate GPS locations. This left us with many less sites actually sampled than we had hoped and planned for. Nevertheless we successfully sampled twenty sites ranging from the upper reaches of the Ogden River in northern Utah to the Sevier River of southern Utah.

When we finished with sampling this fall we then had to obtain the rest of our data from the UDWR. Those data included the fish population information for the sites we had sampled at. This proved especially problematic. Each regional biologist sent us what they “had”. It turned out that some of the sites that they originally directed us to do not have corresponding data. This reduced our effective sample number by about half. Another difficulty we encountered as we sifted through the data was that the different regions record information rather differently from one another and that they often supplied us with different kinds of data and that most of it doesn’t make for accurate comparisons. After compiling what we could of the data it was apparent that we just had to standardize what we could of it. The standardization consists of the relative number of brown trout or native fish species observed, instead of compared the total number of each fish species observed within a site. Even with these problems in using government data, using it saves more time and cost than us having to gather it ourselves via permits and electroshocking.

We are still in the process of readying the data to be entered into the GIS computer program. However, without running the analysis we can see a general trend in the study. Native fish appear to be in greater abundance in streams that have higher late summer turbidity. Once all of the data is formatted correctly and entered into the GIS we will be able to produce the statistics to back up this observation. As with our original field plans we have also altered and improved our methods for running the GIS program.

We now are going to include many other variables in the analysis, which are spatially correlated to our study sites. These data include water use, land use, and possibly vegetation data gathered from satellite images. We intend to publish the finished research in a peer-reviewed journal and present the results at next year’s Utah Chapter American Fisheries Society meeting where many of Utah’s state and federal biologists get together give presentations on field work and research within Utah.

I consider this ORCA project experience to be one of the highlights of my undergraduate experience. I am starting a master’s of biology graduate program this fall and I feel that I will be better prepared for my thesis because of the skills I gained while doing this project. I am excited to present the results of this research and hopefully have them aid the Utah government in managing some of its most special natural resources.

Acknowledgements

I would like to thank the BYU ORCA organization and committee members for selecting my project to receive a grant that made it financially possible to do this project. I also would like to thank Dr. Ryan Jensen and Dr. Dennis Shiozawa for their invaluable mentoring and work on this project.

References

• Belk, M. C., and J. B. Johnson. “Biological Status of Leatherside Chub: A Framework for Conservation of Western Freshwater Fishes.”Status, Distribution, and Conservation of Native Freshwater Fishes of Western North America 53 (2007): 67-76. Print.
• Carter, M. W., et al. “Effects of Turbidity and Cover on Prey Selectivity of Adult Smallmouth Bass.” Transactions of the American Fisheries Society 139.2 (2010): 353-61. Print.
• McDowall, R. M. “Crying Wolf, Crying Foul, or Crying Shame: Alien Salmonids and a Biodiversity Crisis in the Southern Cool-Temperate Galaxioid Fishes?” Reviews in Fish Biology and Fisheries 16.3-4 (2006): 233-422. Print.
• Olsen, D. G., and M. C. Belk. “Relationship of Diurnal Habitat Use of Native Stream Fishes of the Eastern Great Basin to Presence of Introduced Salmonids.” Western North American Naturalist 65.4 (2005): 501-06. Print.