High water temperatures in early August killed 239 spring chinook salmon in the Grand Ronde River, a biologist with the Confederated Umatilla tribes said.
Gary James, fisheries manager for the Confederated Tribes of the Umatilla Indian Reservation, reported that in the last two weeks of July during extremely high temperatures, the CTUIR fisheries staff in the Grande Ronde Basin began observing spring chinook near Starkey on the upper Grande Ronde River. As water temperatures warmed, staff began closely monitoring the behavior and movement of these fish.
Even though the water temperature approached the high 70s in the daytime, many fish were not moving upstream to cooler spawning areas and were not showing negative effects. When staff checked conditions on July 31, James said, temperatures had escalated to near 83 degrees and fish started dying.
Staff began capturing the salmon and hauling them upstream to cooler water. Over the weekend of Aug. 1, fisheries workers hauled 130 adults and 10 jacks upstream. Only one early morning trip per day was possible as water temperatures rose too much to continue handling and stressing fish.
The salvage operation, however, was not able to save 140 adult and 99 jack salmon. James said these fish were holding in some relatively cooler deep pool water that eventually became too hot.
"This incident is not the only recent example of temperature-related fish mortality," James said. "Currently the mortality rate for the 2009 spawning season in the upper Umatilla River is also higher than what has been observed in previous years. A major die-off of spring chinook occurred in the Middle Fork John Day River in 2007 during a hot summer period."
In spite of this incident, James said there is still a large number of salmon getting ready to spawn in the upper Grande Ronde. The 2009 upper Grande Ronde return was highest in recent history and there are an estimated 250 surviving fish in the upper Grande Ronde River at this time, including the 140 fish the emergency trap and haul operation saved.
James and his staff are developing a detailed plan and will coordinate with Oregon Department of Fish and Wildlife in an attempt to prevent this kind of incident from happening again.