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Strong Summer Chinook Counts At Bonneville Dam Diminished By Warm Water Mortalities
Posted on Friday, August 07, 2015 (PST)

A NOAA Fisheries biologist reported this week that summer chinook migration amounted to a record at Bonneville Dam on the Columbia River, but the strong return was significantly diminished by high water temperature mortalities.


“I just wanted to highlight that we had a record return,” said Trevor Conder, referring to his presentation to the Technical Management Team this week. “That indicates we had good ocean conditions and we had good river conditions … The problem is that we got hit with extremely poor river conditions” further upstream in the Columbia River system.


The count of summer chinook adults at Bonneville Dam has tallied about 161,000 fish. The previous highest count was 132,025 fish in 1957, Conder said.


“That was the highest by a large margin,” he said, noting that the highest count of adult summer chinook salmon migrating at Bonneville in recent years was 126,000 fish in 2002.


“The flip side is that the conversion rates to McNary Dam (upstream from Bonneville) were lower than average,” Conder said.


The mortality rates for chinook between Bonneville and McNary are similar to the rates for sockeye salmon, about 54 percent. Recorded mortality rates increase in waters further upstream, particularly for sockeye.


“We are seeing way more loss for Snake River sockeye,” Conder said, referring to the segment of migrating spawners that move into the Snake River system as opposed to those that move into the Upper Columbia River system.

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