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Imnaha River Research Revealing Some Of The Mysteries Of Drainage’s Threatened Steelhead
Posted on Friday, August 11, 2017 (PST)

Steelhead trout research on a remote northeast Oregon river is showing good reason for the fish’s threatened status under the federal Endangered Species Act.


Following 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.


Tracking 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 traps.


“It was starkly evident why these fish are listed, so few came back this year,” Harbeck said.


The 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.


Harbeck 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.


Harbeck said the Imnaha smolt trapping data is part of the collection of information, uploaded in real time to the center’s server and database.


“Therefore 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.


Neal 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.


“There 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.”


The 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.


“We’ve 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.”


Espinosa 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.


“When 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.”


Even within the Imnaha watershed evidence from weirs and PIT tag arrays show steelhead might enter different tributaries multiple times.


“We are learning about when and where they reproduce, what streams are important and what reaches of those streams are most important.” Harbeck said.


One of the most surprising discoveries, Harbeck said, was the large number of steelhead that spawn in the mainstem of the river.


“It’s not just a migration corridor,” Harbeck said.


Research 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.


Gumboot 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 ocean.


Through PIT tag information Harbeck said it appears those kelts don’t do well once they return to the Snake River.


In 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.


Although the highest in 6 years of monitoring, by the time they got to the Bonneville Dam that percentage shrank to nine percent.


Harbeck 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.”


The 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.


The arrays don’t let researchers get their hands directly on fish, but add useful data on the movement and timing of tagged fish.


Harbeck 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.”


Another 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 steelhead refuge.


Understanding 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.


“We 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.”


After 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.


Espinosa 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 fewer species.


Harbeck 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.


To 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.


Besides collecting juvenile steelhead, Espinosa said they recorded information on the endangered fish’s neighbors, primarily tailed frogs, tailed frog tadpoles and sculpin.


“Densities 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.


Harbeck 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.”



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