|Abstract or Summary
- In the fall through spring of 2002/03 and 2003/04, the composition of
fish and amphibian communities were examined in intermittent streams in
the upper Willamette river basin in western Oregon. I recorded standard
aquatic habitat variables and water nutrient concentrations (nitrate and
phosphate) and correlated them with fish and amphibian communities
present. Fish and amphibian communities were also compared between
seasons (winter and spring), capture method (minnowtrap and backpack
electrofishing) and channel morphology (incised and gently sloping
channels). Fish were tagged with visual implant elastomer to assess
movement and distribution. Fourteen species of fish and five species of
amphibians were present in these habitats over two field seasons. Fish and
amphibian species composition and abundance was correlated with
characteristics of the upper Willamette basin. The regional characteristics
associated with the differences were a) the amount of the watershed covered
in forest and b) upstream slope; whereas mean maximum water velocity
separated fish dominated communities from amphibian dominated communities. Approximately 99% of fish and amphibian species caught
were native to the Willamette river basin and the number of fish species
decreased as the sampling distance from perennial water increased.
Significant differences were found in fish and amphibian community
composition between winter and spring and between capture methods.
Surface/mid-water feeding fish were more abundant in gently sloping
channels than benthic feeding fishes. Only 2.6% of the 498 tagged fish were
recaptured between December and April.
In the fall through spring 2003/04, the composition of fish
communities and their invertebrate diets were compared between 12 sites
on four intermittent streams. The distance between consecutive sites was
approximately 900 to 1500-m. Two intermittent streams had incised
channels, confining high flows to a narrow channel. The remaining two
streams had gently sloping channels, where flood waters had access to the
floodplain. Two hundred and thirty individual diets were sampled from
cutthroat trout, northern pikeminnow, redside shiner, sculpin, speckled
dace, threespine stickleback in both winter and spring. About 60% of the
stomach samples contained invertebrates and approximately 90% of them
were aquatic species. There was a significant difference in the numbers of
invertebrates consumed by redside shiners, sculpins and speckled dace.
These three fish species fed most often on benthic invertebrates compared to
surf ace/midwater invertebrates, but only sculpins and redside shiners were
significantly different. However, the proportions of benthic and
surface/midwater invertebrates in the diet of these fish species were not
significantly different between seasons or channel types.
This thesis inventories fish and amphibian species found in
intermittent stream habitats of the upper Willamette basin, and identifies the
main habitat features that influence the distribution of those species. It also
examines the diet composition of a subset of widely distributed fish species.
The findings of this study can be used to understand how land uses, such as
grass seed agriculture, affect intermittent streams, and to design future
studies on the effectiveness of habitat enhancement conservation practices
(such as grassed waterways, residue management, filter strips, streambank
protection, etc.) to improve and/or protect these important seasonal habitats
in the upper Willamette basin.