Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Committee Chair(s)

Charles Hawkins


Charles Hawkins


Phaedra Budy


David Koons


The introduction of exotic species to areas outside of their native range is one of the greatest threats to the biodiversity of native freshwater organisms. Exotic species have outcompeted native species for resources such as food and shelter, and in some cases these interactions have resulted in local extinctions or reductions in abundance of those native species. Brown trout are native to Eurasia, but have been introduced to much of the rest of the world, including the United States. In some parts of their introduced range, brown trout have substantially reduced the abundance and home ranges of some native fish species. In the United States, brown trout have been intentionally stocked in many streams and rivers across the country because they are a desirable sport fish. A few studies have shown that these fish negatively affect some native fish species. However, I found no studies that considered the effect of brown trout on native species across a large portion of their range in the United States.

For my thesis, I examined if the presence and abundance of brown trout have affected (1) the abundance, presence, and distribution of two ecologically different native fish taxa (sculpins and speckled dace) and (2) the composition and relative abundances of entire assemblages of native stream vertebrates in streams across 12 western United States. I found no relationship between brown trout and the abundance, presence or absence, or distribution of either sculpins or speckled dace. I also found that brown trout were not associated with differences in the composition of the native stream vertebrate assemblages. My results imply that native stream vertebrates are able to successfully coexist with brown trout across the western United States, and therefore may not experience the extreme changes in abundance or distribution that some exotic species may cause.




This work made publicly available electronically on November 21, 2011.