Record number of chum salmon pass Bonneville Dam

Spawning chum salmon are making a comeback above Bonneville Dam. In the past three years, the chum population in the upper Columbia River Gorge has nearly doubled each year. This year, over 1,100 chum passed over the Bonneville Dam – making this the largest passage since 1954. BPA operations and habitat investments are supporting the return of this threatened species.

Chum are the most abundantly spawning species of salmon throughout North America's West Coast. In the Columbia River, however, chum have been identified as a threatened species under the Endangered Species Act since 1999.

Columbia River chum are the last salmon to return to spawn and the first to migrate back to the Pacific Ocean. As chum make their way back to the river, they search for areas where warm upwelling water flows through the gravel. The warm water increases the chums' growth rate as they emerge from their nests, often referred to as redds. In habitats below Bonneville Dam, adult chum arrive at the start of November and are typically present throughout December.

In 2000, the National Marine Fisheries Service Biological Opinion identified that spawning areas below the Bonneville Dam were sensitive to its operations. To address this, federal agencies manage Columbia River flows from Bonneville Dam to ensure the chum spawning habitats are adequately filled with water.

Tony Norris, BPA's representative on the regional Technical Management Team that makes recommendations on dam and reservoir operations for the Columbia River, said BPA coordinates with other federal agencies to manage downstream flows from the dam. During the chum spawning phase, the flows below the dam are operated to maintain a specific water surface elevation range during the day. Currently, the U.S. Army Corps of Engineers holds the river below the dam between 11.3 and 13 feet above sea level during daylight hours.

For these operations to occur, water is released 350 miles upstream from Grand Coulee Dam, operated by the Bureau of Reclamation. Norris said management of the system is a balance of long-term water management and hourly operations to accomplish such a precise operation at Bonneville Dam when the water is released so far upstream. 

At BPA, the Geomatics and Geographic Information Services teams have been able to accurately map historical chum spawning locations, and they provide critical information to help river operators protect the redds. These maps focus on historical spawning sites near Ives Island that are directly influenced by operations at Bonneville Dam.

Coordinating with the Pacific States Marine Fisheries Commission's chum monitoring team, Geomatics' land surveyors measure the location, elevation and adjacent water elevation of the chum redds. This information is essential to accurately identify the water surface elevation required to protect the chum when they emerge from their eggs. The Geographic Information Services team then adds that data to a three-dimensional model of the chum spawning areas.

“The GIS visualizations and data have facilitated important changes to how chum operations are managed during periods of low flows in the Columbia River," Norris said.

BPA has also helped fund and maintain off-channel habitat for chum spawning below the dam. Hamilton Creek is a prime example. Feeding into the spawning habitats around Ives Island, Hamilton Creek flows through the town of North Bonneville. A channel of Hamilton Creek was disconnected during the construction of Bonneville Dam's second powerhouse, but the channel still experiences upwelling groundwater after sufficient rainfall has occurred. Chum salmon were found to successfully spawn in this old channel.

In 2011, BPA funded a project to improve the channel and increase available habitat for spawning chum, including the creation of a second fork in the channel. The channel, called Hamilton Springs, provides chum with perfect spawning conditions. A natural filling spring, Norris said the channel is unaffected by operations at Bonneville Dam. In Hamilton Springs, chum salmon emerge at a rate 10 times higher than fish spawned in the mainstem spawning areas.

“BPA has awarded contracts to the State of Washington and others to improve chum salmon habitat. It is encouraging to see the work contribute to the increase in returning adults," said Executive Vice President for BPA environment Fish and Wildlife Scott Armentrout. “We will continue to build on this success and future work will add more opportunity for this species. I am grateful for the hard work BPA staff and contractors have done to make this possible."