A watershed in the south Portland suburbs was
found to have a healthy and diverse population of native coastal cutthroat
trout equal to cutthroats in a pristine mountain stream, according to a recent
The study found that native coastal cutthroat
in Tryon Creek, a tributary of the Willamette River downstream of Willamette
Falls and upstream of Portland, Ore. are represented by all age classes, that
they migrate in and out of local streams, are genetically diverse, are free
from disease, and that these characteristics of the Tryon Creek trout
population were similar to non-urban populations of the trout in the Mt. Hood
Tryon Creek is one of the largest urban
watersheds in Portland, Oregon, a city of more than 650,000 people, where
developed land accounts for 55.6 percent of total land use, the study says. The
stream itself is located in the Tryon Creek State Natural Area and has about 43
kilometers (27 miles) of open streambed and 5 kilometers (3 miles) in culverts
“We found that an urban watershed can support
a healthy population of environmentally sensitive, native fish,” said Brook
Silver, fish biologist with the U.S. Fish and Wildlife Service and one of the
study’s authors. “This example of a relatively healthy fish population in an
urbanized landscape demonstrates the value of habitat conservation. As cities
continue to grow, it will be important to preserve and maintain habitat that
serves to protect sensitive, threatened, and endangered species.”
The study says that the effect of urbanization
is often called urban stream syndrome with symptoms such as altered flow
dynamics, passage barriers, poor water quality and degraded food webs, as well
as an urban condition known as the heat island effect. After protections were
put in place and habitat improvements were made in and around Tryon Creek,
however, the stream is less prone to these symptoms than other urban
“An urban stream can support a healthy
population of coastal cutthroat trout” https://link.springer.com/article/10.1007/s11252-017-0711-0 was published in the journal Urban Ecosystems.
Silver’s co-authors are Michael Hudson, fish
biologist, Christian Smith, geneticist, Kenneth Lujon, fish biologist, and
Timothy Whitesel, fish biologist, all with the Service; and Melissa Brown,
environmental specialist with the City of Portland.
Native fish species found in the creek are
cutthroat and, possibly, resident rainbow trout, the study says. Anecdotal
evidence is that steelhead once spawned in the creek and that juvenile coho and
chinook salmon are using the lower area of the creek near the Willamette River
for temporary rearing.
“Of these species, Coastal Cutthroat Trout
appear to be the most likely self-sustaining natural population of fish in the
stream,” the study says.
The study was done after completing a number
of fish habitat improvements. Some of those improvements by the City of
Portland protect the sometimes steep-banked creek from erosion, others improved
the floodplain fill, hardened creek banks and created shallow water refuges
with large wood and boulder installations, as well as projects that replanted
riparian areas, Silver said.
In 2008, the Oregon Department of
Transportation retrofitted the culvert under Oregon State Highway 43 with a new
baffle system to improve fish passage and provided habitat restoration. In
2010, the city improved floodplain connectivity below the Highway 43 culvert.
“Making large connected habitats a priority
for preservation and improvement may be essential to protecting sensitive
species,” Silver said. “In growing urban areas, it will be important to
integrate the conservation of healthy stream habitats with watershed planning.”
The study was done to monitor the
effectiveness of these habitat improvements made by the Service and City of
Portland’s Bureau of Environmental Services.
“As part of our monitoring, we surveyed the
Coastal Cutthroat Trout population above the Highway 43 culvert,” Silver said.
“We wanted to see if the population health of Tryon Creek’s Coastal Cutthroat
Trout was similar to that of populations of Coastal Cutthroat Trout located in
relatively pristine ecosystems.”
Rehabilitation of essential habitat in
developed urban watersheds, such as Portland’s, can theoretically improve fish
abundance and diversity, the study concludes.
“In the case of Tryon Creek, it may be
particularly important that rehabilitation efforts and habitat quality are
relatively high in the lower portion of the watershed,” it says. “This helps
promote the ability for cutthroat trout to have connectivity with ecosystems
outside of the watershed.”
Areas where large connected spaces are
preserved and maintained, such as the Tryon Creek State Natural Area, may be
fundamental to protecting sensitive, threatened or endangered species in urban
habitats, the study says.
“We realize not all urban watersheds have the
same potential to support healthy fish populations, but it is possible where
opportunities exist,” Silver said. “As cities grow, assets like fish and water
quality often get overlooked. Planning
smart, conservation-minded development will be important to minimize impacts to
natural resources and protect what remains.”