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Higher water temperatures primary cause of early spring Chinook mortality

June 18, 2015

CLACKAMAS, Ore. – Elevated water temperatures are most likely the cause of spring Chinook salmon deaths in the Willamette River and some of its tributaries, according to fish biologists from the Oregon Department of Fish and Wildlife.

Spring Chinook salmon typically die in the fall after they have spawned. However, some also die before they are able to spawn as the result of stress, disease, and predation. This year, Chinook are dying earlier than usual, according to Tom Friesen, manager of ODFW’s Upper Willamette Research, Monitoring and Evaluation Program.

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.”

ODFW biologists say that high water temperatures likely contributed to the death of the fish.

Chinook salmon are more prone to disease, injury, and stress when water temperatures exceed 60° F. At 70°, the fish start to get into real trouble.

For the past week, water temperatures in the Willamette River have risen steadily, from 70° to 74° F. During the same period, Clackamas River water temperatures rose from 62° to 64° while the Santiam rose from 62° to 66°.

“We get concerned about the impact on Chinook anytime water temperatures approach 70 degrees,” said Friesen.

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.

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.”




Tom Friesen (541) 757-5151 | Rick Swart (971) 673-6038

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