Already in trouble, endangered Snake River sockeye will face serious migration challenges from climate change, according to a new study by NOAA's Northwest Fisheries Science Center.
The study finds that under current management practices, adult sockeye survival will drop by 80 percent by the 2040s due to predicted changes in summertime water temperatures and flow levels. Snake River Chinook runs will drop by between 4 and 15 percent, it concludes.
Adult sockeye would need to migrate two weeks earlier to maintain survival rates from 2008 to 2017, according to the findings. The sockeye run in those years ranged from 440 to 2,786 fish migrating past Lower Granite Dam, the eighth and final dam on their first leg of the journey to Idaho's Redfish Lake in the upper reaches of the watershed.
The study—"Snake River sockeye and Chinook salmon in a changing climate: Implications for upstream migration survival during recent extreme and future climates"—was published Sept. 30 in PLOS One.
"In the Columbia Basin, nearly all hydrosystem planning has focused on flow and spill rather than temperature, despite the enormous sensitivity of salmonids to temperature," the study stated.
Lisa Crozier, a NOAA research scientist and lead author of the study, told Water Power West the study basically confirms that summer 2015—which brought extremely low flows and record-warm water temperatures—was, indeed, a dress rehearsal for Columbia River conditions that will occur with increasing frequency from climate change.
The year started with record-low mountain snowpack followed by a dry spring that resulted in severe drought, mega-wildfires and heat waves on land and at sea. Overall, air temperatures were 3.4 degrees Fahrenheit above normal, with wintertime temperatures 6.2 F above normal. Temperatures warmed the Columbia River to more than 70 F in July, contributing to the death of an estimated 250,000 adult sockeye as they attempted their journey to spawning areas in the upper reaches of the Snake and Columbia rivers.
According to a NOAA Fisheries report on the die-off, flows and water temperatures in the Columbia River in June resembled conditions normally seen in late July and August. The impact was especially harsh between Bonneville and Lower Granite dams, where 95 percent of the ESA-listed Snake River sockeye perished.
"In 2015, temperatures pretty much went back to normal in August, and everybody breathed a big sigh of relief," Crozier noted. But with climate change, August will not always bring that relief, she noted. While the new normal will vary from year to year, a large percentage of years will be hotter than they are now, she said.
By the 2040s, adult sockeye, which migrate in midsummer, will likely experience temperatures higher than 19 C (66 F) at Bonneville Dam, rising to 21 C (69.8 F) by the time they reach Ice Harbor Dam and to 23 C (73.4 F) when they hit the lower Salmon River, according to the study.
"In some cases, major declines in summer flow exacerbated the impacts of temperature change, particularly in the free-flowing section of the migration route upstream of the hydrosystem," it said. Warm water can be lethal to salmonids, so the water temperature standard at lower Snake and Columbia river dams is 20 C (68 F) to protect spawning, rearing and migration.
In 2015, the vast majority of Snake River sockeye died before reaching Lower Granite Dam. But the study noted, "The largest changes in temperature and flow are projected to be upstream of the hydrosystem, where direct mitigation through hydrosystem management is not an option."
Crozier said upstream locations in the Snake River are likely to be warmer and have lower flows than those downstream partly because the streams are smaller, so air temperatures will cause more warming and evaporation. In addition, they're located in the arid interior, where summers are expected to become hotter and drier.
The study looked at survival impacts to sockeye and Chinook during migration. And while sockeye are at much higher risk from migratory challenges posed by climate change, Chinook will face their own challenges once they reach the spawning grounds, Crozier noted.
The majority of the Snake River spring-summer Chinook run migrates before river temperatures become a problem, she said.
"Historically, their largest problem is high flows. But they do face a temperature problem. They move quickly up into those high elevations, and they find a nice deep pool and wait until August, and then they spawn," she said.
Warmer stream temperatures and lower flows in August will likely have a greater impact on their spawning success, or pre-spawn mortality, which wasn't evaluated in this study. That's where sockeye have an advantage.
"For Snake River sockeye, we expect less change in pre-spawn mortality because they return to a deep, cool lake," the study said. "[M]ajor biological costs for sockeye will likely accrue during the migration stage."
For the study, scientists used the life histories of 17,279 Snake River sockeye and spring-summer Chinook and the human-caused stresses they face now from hatcheries, habitat, hydropower and harvest, and used climate change models specific to the Columbia Basin to ascertain how they'll fare in the future.
The study quantified survival of Snake River sockeye and Chinook during their migration from Bonneville Dam to their spawning grounds under those future climate conditions.
Looking back at 2015, it may seem like there's little hope for Snake River sockeye. But Crozier said that's far from the case.
"This study says if we don't change anything, this is the likely outcome. But there are many pieces we can address," Crozier said. "It's not that there's no hope. It's really just a call to action. There are many things we can do."
She said continuing efforts to restore wild Snake River sockeye could do a lot to build a population that is more resilient and sensitive to migration timing. "Snake River sockeye have likely lost much of their adaptive capacity with the loss of the wild population," the study said.
Crozier said another study showed that upper Columbia River sockeye have been shifting toward an earlier migration period, largely as an evolutionary response to thermal selection. A wild stock of Snake River sockeye could have that potential, too, she said.
Snake River sockeye transported downstream as juveniles have much lower adult survival rates than those that remain in the river, so that management decision should also be considered, she said.
"Further work exploring habitat restoration or additional mitigation actions is urgently needed," the study stated.
Crozier said planting vegetation to shade streams in the upper reaches, reconnecting flood plains and reestablishing beaver ponds could also help restore cooler streams.
She said dams could also be managed in ways that will help cool the river at times when it's most needed, which is already being done with Dworshak Dam. "They have the models to do this," she said.
Crozier said there is no single solution to preparing for impacts of climate change. "It needs to be a regionwide effort. I think no single agency can do this. We need the public to understand the scale of the problem, and how important it is."