Salmon die-off in Wilson River from parasite leads to fishing closure, hits population

Zach Urness | Statesman Journal

A recent die-off of fall chinook salmon in the lower Wilson River has led to a fishing closure effective December 7 to 31.

At least 200 salmon, and likely more, were found dead in the river near Tillamook before getting a chance to spawn, according to the Oregon Department of Fish and Wildlife.

The cause is the parasite cryptobia, which spreads during the low water conditions seen this autumn, as fish get concentrated into smaller pools and are unable to swim upstream, officials said.

“The fall Chinook run is below average to begin with this year, so this substantial loss of fish could affect recruitment of fish for future years,” said Robert Bradley, a fish biologist for the Oregon Department of Fish and Wildlife based in Tillamook.

“Current river conditions are expected to continue for at least a week, which is likely to contribute to further loss of potential Chinook spawners from the parasite,” he said.

Bradley said the parasite hasn’t been seen in other basins yet and no “substantial mortalities have been observed in other rivers on the north coast to date,” he said.

The parasite does not affect humans, officials said.

While salmon die-offs have occurred during the past decade, it’s typically during summer drought periods rather than late autumn. November is normally one of Oregon’s rainiest months.

But northwest Oregon has seen historically dry conditions this season — it was the fifth- driest November in 125 years of records for Portland and Astoria, according to the National Weather Service.

Drones: As drones increase at Oregon's state parks, even at a nude beach, where can you fly?

Silver Falls: Silver Falls to get new trail, viewpoint and access near North Falls for 2022 celebration

“We’ve had several die-offs in the summer months, but that’s been mostly temperature related,” ODFW spokesman Rick Swart said. “I can’t think of one in my 11 years happening in what’s pretty close to winter. But what they were seeing was that the lower levels, the smaller pools and the higher concentration of fish meant a lot more spread (of the parasite).”

The dead fish were discovered earlier this week. Fish biologists surveyed the lower river and found a minimum of 200 dead, pre-spawned adult Chinook.

“Evidence of scavenging and deeper holes with limited visibility likely means the number of mortalities is higher than observed,” a news release said. “Examination of chinook carcasses confirmed the presence of cryptobia.”

It’s unclear what impact the die-off will have long term on the native fish runs of the Wilson River.

“They were good healthy-looking fish that never got upstream to lay eggs, and what this means for the river’s wild chinook population, we’re not sure,” Swart said. “It will obviously mean fewer eggs in the gravel, and now there’s concern about a big flood washing out what was there. But it could mean less competition, too, so we’ll have to see.”

The fishing closure is from the confluence with Blind Slough (in tidewater at river mile 0.5) upstream to Jordan Creek. The river upstream of Jordan Creek is already closed to salmon angling by permanent rule. Angling for steelhead is unaffected by this change and remains open under permanent regulations.

Zach Urness has been an outdoors reporter, photographer and videographer in Oregon for 11 years. To support his work, subscribe to the Statesman Journal. Urness can be reached at zurness@StatesmanJournal.com or (503) 399-6801. Find him on Twitter at @ZachsORoutdoors.