The Great Escape
©The Register-Guard - Used With Permission
BLUE RIVER - This is a fish story about the little ones that got away.
It's about how some of these little guys will one day return as big ones. And about how their escape may contribute to a comeback for their beleaguered species.
The heroes of this story are spring chinook salmon smolts, some 14,000 or more of them. Just 1 to 2 years old, most are only as long as a man's thumb or forefinger.
The supposedly "landlocked" salmon escaped from Cougar Reservoir between mid-November and the end of January. The getaway was documented by two fish traps - one placed below the dam's powerhouse, the other below a spillway outlet.
What makes their story worth telling is that these smolts are members of one of the nine families of fish proposed for listing under the federal Endangered Species Act. The National Marine Fisheries Service on Tuesday recommended that upper Willamette spring chinook be listed as a "threatened species."
Beyond that, these smolts were born in a stream where, for nearly 30 years, not a single salmon had spawned. Construction of Cougar Dam in 1963 blocked upstream-migrating chinook, and a plan to trap salmon below the dam and truck them to their spawning streams was abandoned a few years later.
Adult salmon were reintroduced to the upper South Fork in 1993, but not with any hopes that significant numbers of their offspring salmon might someday escape from Cougar Reservoir and make their way down the McKenzie, Willamette and Columbia rivers to the Pacific Ocean.
Rather, biologists were simply trying to help another species in trouble, the bull trout. Before the dam was built, young salmon had been a staple of the bull trout's diet. Biologists also believed nutrients from the carcasses of spawned-out salmon would benefit the ecosystem.
A total of 1,493 adult chinook were released above the reservoir in four different years - 1993, 1996, 1997 and 1998.
However, it was as an afterthought that biologists decided to find out whether any of the offspring of those spawning adults might be making it out of the reservoir.
What they discovered in their traps left them surprised and elated.
"We didn't expect to see this many chinook," said Mark Wade, assistant district biologist for the upper Willamette district.
"Our assumptions before we started doing this was that the outlets on this dam were too deep," Wade said. "Salmon are surface-oriented and we didn't think they'd find the opening. We thought they'd be trapped in the lake."
Cougar Dam had been designed to allow smolts to migrate downstream through a series of openings, chutes and tubes. But that system had been shut down in the 1960s after it was found to be ineffective.
Most of the young salmon could never find the so-called "fish-horn" openings.
All water leaving the reservoir is collected by an intake structure - a giant concrete tower in the dam's forebay. Picture an elevator tower with seven sets of doors. The top five doors were the fish horns. (Different doors would be opened depending on the water level in the reservoir, which fluctuates by about 170 feet each year.)
Worse, up to 70 percent of the young fish that used the fish horn openings were mortally injured as they fell through the elevator shaft and emerged at the base of the dam.
With that system shut down, there are only two routes that smolts could use to escape the reservoir. They could dive to the "basement" of the elevator shaft and enter a tunnel leading to the powerhouse and the turbines. Or they could use the second opening from the bottom, the "regulating outlet."
That outlet leads to a tunnel through the canyon wall and to a series of chutes. It functions like a spillway and is opened only when the Army Corps of Engineers needs to release more water than the turbines can handle.
This winter's trapping found both routes were being used. A total of 467 smolts were captured below the powerhouse and 1,165 were in the regulating outlet trap.
By releasing known numbers of marked fish, biologists established that the two traps catch about 10 percent of all fish moving downstream. Hence the estimate of a 14,000-smolt escapement.
Researchers say it's a minimum number because there were several days when the flow in the regulating outlet flow was so heavy that the trap got "blown out."
Not only did hundreds of fish show up in the traps, but the smolts survived their hazardous journey through the dams in reasonably good shape. The mortality rate on fish in the trap below the turbines, for example, was seven percent, Wade said.
"A typical fish moving past Leaburg Dam in the fall is around 10 centimeters (four inches) long," Wade said. "Coming out of Cougar, we had a bunch between 12 and 16 centimeters, so they're growing real well."
Given a typical survival rate for salmon smolts, about one percent of the Cougar escapees would be expected to survive the journey to the sea and back.
The prospect of an additional 140 or so adult salmon returning to the South Fork may not sound like much - until you consider that the wild chinook run in the McKenzie has fallen as low as 1,300 adults in recent years.
The significance of the Cougar trapping results is not lost on Jim Martin, the ODFW biologist in Portland who oversees fish protection efforts in the Willamette Basin.
"I'm extremely excited with these results," Martin said. "To me it's a startling success - we don't have any other examples where there's even a hope, under current technology, of getting fish down through a dam like that. These results indicate it may not be as technically daunting as we first thought."
He said the fact that Cougar Reservoir is already producing smolts adds "a lot of impetus" to the move to restore a wild run in the South Fork McKenzie basin.
Martin expects the Cougar chinook will be covered by the Endangered Species Act - even though their parents were trapped at McKenzie hatchery.
"My assumption is those would be considered wild fish," he said. (All hatchery-reared chinook are now marked with a clipped fin; those with no clipped fin will be considered wild.)
Martin said the state will push hard to have the National Marine Fisheries Service designate the streams above Cougar as "critical habitat" for threatened chinook.
"The major loss (of salmon production) in the McKenzie occurred when we built Cougar," Martin said. "The loss occurred because of two factors. One was we cut off access to the best habitat. Secondly, we altered the flow and temperature regimes in the downstream segment."
Water drawn from the bottom of the reservoir is too cold at some times of the year, too warm at others. As a result, salmon eggs have been hatching too early, when there is little food available for the fry to eat.
The ODFW believes the first key to spring chinook recovery is "to be able to re-access the South Fork and to modify those damaging flow and temperature regimes," Martin said.
The Army Corps of Engineers is already working on the design phase of a $70 million temperature control facility. If Congress appropriates the money to build it, construction will begin in 2001, according to Wade Stampe, manager of the Corps of Engineers' upper Willamette flood control projects.
Stampe said he agrees with ODFW biologists that the temperature control tower should include provisions for downstream fish passage.
The Corps may be able to help more salmon smolts escape. It may be possible to adjust the timing of water releases through the regulating outlet to more closely match peak migration times, Stampe said.
"As far as I'm concerned, we should do anything we can that adds to the survival of these fish."
A COUGAR CHINOOK CHRONOLOGY
1959: Oregon Fish Commission biologists estimate that 3,960 adult spring chinook salmon spawn in the South Fork McKenzie River above Cougar Creek, site of a new flood-control dam.
1962: 2,121 adult chinook return to the South Fork, are trapped and transported around the construction site. They account for one out of every 12 chinook counted at the Willamette Falls Fish Passage at Oregon City.
1963: Cougar Dam completed.
1965: Salmon returns decline dramatically - only 65 adults return to the trap in the Cougar Dam tailrace and are passed upstream.
1969: After four years of study and attempted fixes, officials conclude Cougar Dam's "fish horn" passage system will never work as designed; construction of additional salmon hatchery capacity to mitigate for loss of spawning habitat is recommended.
1993: Biologists begin releasing surplus adult salmon from McKenzie hatchery to spawn in the South Fork above Cougar Reservoir. Ironically, the move is seen as a way to increase food supplies for the bull trout, another species eligible for Endangered Species Act protection.
1995: Army Corps of Engineers proposes retrofitting Cougar Dam with temperature control tower to regulate temperature of water discharge. Proposal prompted by scientists' conclusion that abnormal water temperatures in the McKenzie River contribute to salmon's decline.
1999: Biologists surprised and elated to learn thousands of spring chinook salmon smolts survive trip through the turbines and regulating outlet. Discovery, coupled with listing of Willamette Spring Chinook for protection under Endangered Species Act, adds impetus to move to retrofit dam with a workable fish passage system.