Scott Swanson
What happens to Chinook salmon after they leave the U.S. Army Corps of Engineers’ new $18.6 million fish transfer facility on the South Santiam River?
That’s a question that University of Idaho fisheries biologists are trying to answer in an ongoing study that brings them periodically to the facility at Wiley Park.
A trio of scientists were at the fish trap Friday morning, June 19, busily tagging, measuring, weighing and inoculating wild salmon that have entered the facility after their swim in from the ocean. The tags they insert help track the fish once they leave the facility.
George Naughton, who leads the reasearch team, said the point of the research is to determine what happens to fish between their departure from the facility and when they spawn upstream.
“We want to see if they’ve spawned or not,” he said. “A lot of them do spawn, but some years there’s a high pre-spawn mortality.”
He said the researchers gather the data at the South Santiam and others, including Fall Creek, Dexter and Minto (Marion Forks) hatcheries.
“We’re pretty mobile,” he said. “We’re all over the place.”
The study dates back to 2008, when a single University of Idaho graduate student began tracking salmon and steelhead behavior on Cedar Creek. It was prompted by dramatic declines of Pacific salmon and steelhead in the Columbia and Snake rivers and their subsequent protection under the U.S. Endangered Species Act in the 1990s.
They record each wild fish’s length, weight, fat, body shape and other variables, such as water temperature in an attempt to assess what factors might be contributing to fishes’ survival or lack thereof.
A big one is water temperature, Naughton and other fish biologists say.
“A lot of it comes down to water temperatures,” he said. “We may see some significant mortality this year, with low flows and high water temperatures. 18 degrees (Celcius – 64.4 Fahrenheit) seems to be the tipping point. Twenty degrees (68 F) is lethal.
Oregon Department of Fish and Wildlife biologists say elevated water temperatures are most likely the cause of spring Chinook salmon deaths in the Willamette River and some of its tributaries already this year. This year, Chinook are dying earlier than usual, according to Tom Friesen, manager of ODFW’s Upper Willamette Research, Monitoring and Evaluation Program.
Spring Chinook salmon typically die in the fall after they have spawned – if they don’t perish before they are able to spawn as the result of stress, disease, and predation.
ODFW biologists and survey crews have observed unusually large numbers of spring Chinook salmon carcasses in the Willamette, Clackamas, and Santiam rivers recently.
“Pre-spawning mortality is normal and happens every year to some extent,” said Friesen. “But usually we don’t see dead spring Chinook in the mainstem Willamette until mid-summer.”
For the past week, water temperatures in the Willamette River have risen steadily, from 70 to 74 degrees Fahrenheit, while the North Santiam rose from 62 to 66 degrees.
Brett Boyd, manager of the South Santiam Fish Hatchery, said temperatures in the South Santiam are colder – averaging about 64 degrees recently – than in the lower stretches of the river and in the Willamette, which are warmed by in-flow from other streams.
If forecast drought conditions and elevated water temperatures persist, some spring Chinook will likely continue to die before they have a chance to spawn, especially in the mainstem Willamette and lower portions of tributaries, ODFW officials say.
The good news is that the Willamette basin is experiencing one of the strongest spring Chinook salmon returns in years. Through June 13, more than 51,000 Chinook had passed upstream through ODFW’s fish counting station at Willamette Falls, exceeding the 50-year average of 41,000 Chinook.
“Fortunately, many of this year’s spring Chinook have already entered the tributaries, which should help ensure their survival,” Friesen said.
Despite higher than normal water temperatures, most of the region’s hatcheries are doing well and are on track to meet their brood stock needs, according to Manny Farinas, ODFW’s North Hatchery Group coordinator.
“Throughout the region our hatcheries have been experiencing higher water temperatures earlier in the season,” added John Thorpe, ODFW’s Willamette South Hatchery Group coordinator. “We had planned for this and have successfully adjusted fish husbandry practices to respond.”
Naughton said they’re still “early” in the study on the South Santiam but have been at Fall Creek since 2008 and 2009 in the North Fork of the Middle Fork Willamette. He said the Fall Creek studies have shown that “annual female prespawn mortality was strongly associated with mean daily water temperature” during summer months. In the Middle Fork, however, Naughton said, there was less evidence for a temperature effect. Unlike Fall Creek, he said, temperatures in the Middle Fork rarely reach or exceed 70 degrees.
“A primary focus of our work in the South Santiam is to look at the feasibility of releasing fish in Foster Reservoir to help minimize their exposure to warmer river conditions,” Naughton said. “ We’re a little early in the study to draw any conclusions but the fish released into the reservoir last year were exposed to lower temperatures than in-river releases.”