Die-off Sparks Questions On Sturgeon Survival In Changing Climate

Aug 3, 2015

Salmon are a touchstone in the Northwest...in food, in nature, and now, in the damage wrought by the ongoing drought: less than half of returning Sockeye are expected to survive to the end of summer. But another important fish is dying in unprecedented numbers too: the massive white sturgeon native to the Columbia River.

More than 180 mature sturgeon died likely as a result of high water temperatures and low flows that leave less oxygen in the water for fish to breathe.
Credit Rowan Moore Gerety / Northwest Public Radio

Department of Fish and Wildlife biologists Paul Hoffarth and Mike Ritter cut the engine on their motorboat to get closer to a dead fish on the banks of the Columbia River.
Holding his breath in the stench, Hoffarth uses a long gaffing pole to size up the massive fish. “It’s longer than my measuring tape,” he says.
White sturgeon are the second largest freshwater fish on the planet...Even in death, they’re a sight to behold. This sturgeon washed up among the reeds on the riverbank outside Kennewick. Just an inch shy of nine feet, it almost looks like a shark that escaped from an aquarium. It has a mouth like a suction-cup, a pale belly, and tooth-like ridges all down its spine.
Ritter and Hoffarth both say specimens like this one have surprised people who grew up nearby. “People didn’t realize we had fish like this in the river,” Ritter says. “It’s like Bigfoot,” Hoffarth adds. “People think they’re out there, but to actually see one?”
Since mid-July, more than 180 large sturgeon have turned up dead in the Columbia River basin: regulators responded by closing sturgeon fishing indefinitely on most of the Columbia. The die-off now appears to have tapered off. And while it’s too soon to know exactly why it began, Hoffarth says it’s likely that the fish succumbed to a “perfect storm” of stressors earlier this month.

Mike Ritter acts as a spotter on a survey boat looking for dead sturgeon in the Columbia River
Credit Rowan Moore Gerety / Northwest Public Radio

To start, high water temperatures and low flows leave less oxygen in the river for fish to breathe.That’s proven a deadly combination for salmon too--less than half of returning Sockeye are expected to survive on the Columbia through the end of summer.
For sturgeon, the additional stress of spawning and feeding on diseased Sockeye may have put them over the edge.
Hoffarth says the loss of so many large fish is especially worrisome because sturgeon reproduce slowly. “It’s not just something that you can just go out and reproduce in a hatchery and release in a few years, I mean, these fish are 30, 40, 50 years old. It’s gonna take us a very long time to rebuild this population.”
The die-off affected just 1 or 2% of the breeding population on parts of the Columbia. But even that is unprecedented: earlier events, in Canada in the 1990s, and on the Columbia in 2013, involved much smaller numbers of fish.
Now, researchers are trying to understand the likelihood of more heat-related die-offs in the future. “At this point, I think that one year of bad conditions is part of natural variability,” says Ingrid Tohver, a research scientist with the Climate Impacts Group at the University of Washington. “But we’d like to point to this year as a window of what we can expect to become the new normal by the mid-to-end of this century.
Scientists with the US Geological Survey are now collecting data on the Willamette River in Oregon for that very reason: to use this year as a test case for what climate models tell us about the future.
Blaine Parker, a biologist with the Columbia River Intertribal Fish Commission, says climate change poses a particular challenge for sturgeon. On the one hand, they’re survivors: “They were around before T. Rex was around, so it’s a design that works,” Parker says.
On the other hand, large dams have taken away their freedom to move around. Historically, Parker says, “If there was something wrong with a river, they could always drop out of that river.” But most sturgeon in the Columbia are penned in between dams. Combine that with higher water temperatures throughout the summers, and Parker worries it may be too much for Columbia River sturgeon to handle.