trout research on a remote northeast Oregon river is showing good reason for
the fish’s threatened status under the federal Endangered Species Act.
a low steelhead run prediction few tagged fish were tracked coming over
Bonneville Dam in 2016 and fewer still showed up in the Imnaha River this
spring, one of the Snake River’s most productive tributaries.
adult steelhead isn’t easy; they spawn during spring high flows that hamper
trapping and spawning ground surveys. This year was an exceptionally high water
year on the Imnaha - one of two adult weirs managed by Nez Perce Tribal
Fisheries was out of commission approximately 15 percent of the March through
June field season. Jim Harbeck, Nez Perce Tribe’s Joseph field office
supervisor said even when the weirs were operating few steelhead swam into the
was starkly evident why these fish are listed, so few came back this year,”
tribe has long had a vested interest in the salmon and steelhead runs in the
Imnaha River, once an important watershed for Chief Joseph’s Wallowa band. As
salmonid numbers declined throughout the Snake River basin in the 20th century
the Imnaha maintained a reasonably viable steelhead population and proved to be
a good drainage to study.
said in 1992 the tribe began monitoring steelhead smolts at a screw trap four
miles upstream from the Imnaha and Snake River confluence at Cow Creek with
funding from the Lower Snake River Compensation Plan. In 1994 direct funding to
monitor natural and hatchery steelhead was provided by Bonneville Power
Administration as part of the larger “Smolt Monitoring by Non-Federal Entities
Project,” helping the tribe support and participate in the Fish Passage Center
data collection efforts in the Columbia River basin.
said the Imnaha smolt trapping data is part of the collection of information,
uploaded in real time to the center’s server and database.
the timing, survival and abundance of the Imnaha chinook salmon and steelhead
smolts play an important role in the operations of the federal Columbia
hydro-system,” Harbeck said.
Espinosa was the lead field biologist at the Cow Creek smolt trap for 11 years
before helping launch the Imnaha River Steelhead Status Adult Monitoring that
focuses on the river’s upper tributaries. Espinosa said data gaps in the
juvenile research determined more information was needed on Imnaha’s adult
steelhead. In 2010 Espinosa and Harbeck put together a research proposal that
would use PIT tag arrays, weirs, and spawning ground surveys to collect data on
the adults returning to spawn as well as temperature and flow measurements.
are six major population groups in the Snake River Basin,” Harbeck said. “The
reality was there wasn’t a lot known about wild Imnaha steelhead, especially up
high up in the watershed.”
tribe’s researchers set out to learn what they could about abundance,
productivity, distribution and life history characteristics. Six years into the
project, some of the most exciting results come from tracking tagged juvenile
fish returning from the ocean as adults.
learned a lot about Imnaha steelhead and one of the more interesting findings
is that they are wanderers,” Harbeck said. “They do not necessarily all return
directly to the Imnaha all the time.”
said one adult steelhead tagged as a smolt at the Cow Creek trap was an extreme
example of how the species seeks out cold water refuge during its migration
from the ocean. Instead of heading into the warmer water from the Snake River
where it meets the Columbia, it headed north, ending up in the Okanagan River
Basin just below the Canadian border before turning around and finding its way
back to the Imnaha.
we noticed that fish were temporarily straying into non natal tributaries, we
started looking at temperatures of the Columbia and Snake rivers,” Harbeck
said. “It looks like there is a relationship between when they miss the turn
and the temperature difference.”
within the Imnaha watershed evidence from weirs and PIT tag arrays show
steelhead might enter different tributaries multiple times.
are learning about when and where they reproduce, what streams are important
and what reaches of those streams are most important.” Harbeck said.
of the most surprising discoveries, Harbeck said, was the large number of
steelhead that spawn in the mainstem of the river.
not just a migration corridor,” Harbeck said.
on two of the upper Imnaha River’s other easily accessible tributaries,
Mahogany Creek and Dry Creek, wrapped up after just three seasons. The most
significant finding was how well steelhead recolonized Mahogany Creek after a
culvert replacement. As far as Dry Creek is concerned, Espinosa said steelhead
spawn there, but its name isn’t a misnomer - steelhead redds can be quickly
dewatered if spring flows subside prior to juveniles emerging from the gravel.
and Freezeout creeks, where the crew set up traps this year, are what Espinosa
called moderate producers. Scales are collected to determine a fish’s age and
how many times it spawned. There is growing evidence that the Imnaha is home to
a large numbers of kelts, or steelhead that survive spawning return to the
PIT tag information Harbeck said it appears those kelts don’t do well once they
return to the Snake River.
2014, some 67 percent of the fish that passed upstream of the tributary weirs
came back downstream and were passed below those weirs. Of the 148 PIT tagged
adults detected in the upper Imnaha, 41 percent were detected as kelts
migrating back down the Imnaha River.
the highest in 6 years of monitoring, by the time they got to the Bonneville
Dam that percentage shrank to nine percent.
said, “Snake River steelhead have one of hardest journeys of any steelhead
population and have to go through eight dams to get to and from the ocean.”
tribe’s nine PIT tag arrays help track tagged fish on the Imnaha River system
when high water make weirs unusable and spawning ground surveys dangerous or
impossible. PIT tag detections can tell the crew how many fish enter the
stream, how long the fish are in the tributary and the timing of when the first
and last fish enters the creek.
arrays don’t let researchers get their hands directly on fish, but add useful
data on the movement and timing of tagged fish.
said, “One thing I like about project is we have so many sources of data and
are not narrowly focused on one thing – we are gathering information from as
many sources as we can get.”
revelation through the upper Imnaha study is how few hatchery fish make their
way to the Imnaha’s upper tributaries, making it in some fashion a wild
water temperature differences throughout the basin is crucial to the study and
Harbeck said his crew is starting to deploy more water temperature recorders in
streams throughout the Imnaha basin. As part of a more holistic take on the
research, Harbeck said the crew is stepping back and considering the watershed
from an ecological perspective to link habitat with spawning and rearing.
are trying to take a broader look,” Harbeck said. “We want to know where these
fish actually live - that’s the part that connects juveniles and adults.”
the weirs were removed in June, part of that broader look Harbeck mentioned
included collecting specimens of the juvenile steelhead’s primary food source,
macro-invertebrates, from three reaches on Gumboot Creek. After a preliminary
examination, Harbeck said it appears that there is more diversity at the higher
reach than the middle or lower reach.
surmised a flood that took out streamside vegetation 20 years ago on the middle
and lower end of Gumboot Creek could be the reason; less viable habitat means
said when they started looking into the communities where steelhead rear,
studying their food source was just part of it. Finding out where the juveniles
were rearing was another piece of the puzzle.
get better information, Espinosa lead a crew up a reach of Gumboot Creek at the
end of June. He slipped an electroshock backpack over his shoulders and slowly
waved the wand across the width of the stream as three crew members stood
facing him with nets, ready to scoop up any stunned aquatic species, while
another crew member stood close by with a bucket to collect the quarry. The
crew surveyed three different 150-meter sections over three days.
collecting juvenile steelhead, Espinosa said they recorded information on the
endangered fish’s neighbors, primarily tailed frogs, tailed frog tadpoles and
and age classes were more varied higher up than lower down,” Espinosa said. Near
the mouth of the Imnaha there is higher diversity of fish where non-native,
warm water species like bass and sunfish mingle with native coldwater fish. The
findings at both ends of the river create synergy between the two projects.
said, “At Cow Creek we are monitoring juvenile steelhead as they leave the
Imnaha which in turn provides us great ancillary information on the adults –
they are the same fish just at different life stages.”