Columbia River Chum Salmon

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RELATED INFORMATION • Summer Chum Salmon Conservation Initiative (SCSCI) Report Series • Recreational Salmon Fishing • SalmonScape • Salmonid Stock Inventory (SaSI)

Abundance

The annual historic run size to the Columbia River was estimated to be 1,392,000 chum salmon. In 1951 the chum salmon run size on the Washington side of the Columbia River was estimated at 25,000 adults. Since 1959, the population has been relatively stable with the annual minimum chum salmon run size ranging from 300 to 5,700 adults. Preliminary data from 1999 would suggest that the minimum run size is estimated to be near 3,000 adults. Current run size is less than 3% of historic run size, and is less than 12% of the 1951 run size.

Distribution

Chum Salmon were distributed from the mouth of the Columbia River to Walla Walla River. Most of the historic distribution was confined to below Celilo Falls, which is near River Mile 200 on the Columbia River located just upstream of The Dalles Dam.

Current distribution is similar to the historic distribution, with annual runs of chum salmon passing Bonneville Dam. No chum salmon have been observed above The Dalles Dam in more than 10 years. However, before the mid 1980's chum salmon were occasionally observed above The Dalles Dam.

Chum salmon distribution in Lower Columbia River tributaries is often limited to the lower 1/3 of the mainstem and tributaries in this area due to the high gradient nature of Lower Columbia River tributaries.

Populations

Male chum salmon with spawning colors Female chum salmon with spawning colors

Historically every major and some minor tributaries to the Columbia River had chum salmon populations. On the Washington shore, a 1951 assessment identified thirteen self-sustaining populations with run size estimates above 300 fish.

Currently, two population centers exist for chum salmon. The lower is located in the Grays River area and is likely maintained by populations using Crazy Johnson and Gorley Creeks, which are tributaries to the lower Grays River.

The second population center is located below Bonneville Dam and consists of spawners in Hamilton Creek, Hardy Creek, and the mainstem of the Columbia near Ives Island.

Observations of chum salmon still occur in most of the thirteen basins/areas that were identified in 1951. However, there are usually less than 10 fish observed in these areas. It is unclear if these are self-sustaining populations or are composed of strays from other more productive areas.

If the origin of fish in these other basin are composed of primarily strays, then the number of self-sustaining populations on the Washington shore has decreased from thirteen to two during the last 50 years.

In 1999 WDFW located another Columbia River mainstem spawning area for chum salmon located near the I-205 bridge.

Life History

Male chum salmon battling for dominance on the spawning grounds

Entry of adults into freshwater at the mouth of the Columbia occurs from October through December. Entry into Grays River peaks in November. At Hamilton and Hardy Creeks entry is later, peaking in December.

Peak spawning time is from mid-November to early-December on Grays River. Spawning peaks later for the Hamilton and Hardy populations and its peak is generally in late December.

Emergence is likely to occur between February and April. Outmigration occurs from March through May of the same year. Peak outmigration from Hardy Creek occurs in April.

Age at maturity ranges from three to six. Most chum salmon return as age 4 fish. Jacks (age 2) are rare.

The southern extent of chum salmon is only to the mid-Oregon Coast. Since Columbia River chum salmon are near the lower limit of their range, they may be less productive and more vulnerable to extinction risk.

Hatcheries

Historic release of hatchery chum salmon have occurred within this region. The only hatchery program currently operating in this region is the Grays River/Chinook River program. Its purpose is to develop a local broodstock for rebuilding chum populations near the Grays River area and to lessen extinction risk due to catastrophic events. WDFW is finalizing a Hatchery and Genetic Management Plan for this program that will provide more details.

Habitat

Self-sustaining populations of chum salmon are primarily found in modified habitats. Some habitats were specifically modified to increase chum salmon production such as the Gorley Creek and Hamilton Creek spawning channels.

Habitat modification has also occurred in Hardy Creek with major channel moving and in Ives Island area during the construction of the Bonneville Dam Second Powerhouse. Although the intent of these projects was not to increase chum salmon abundance, we have observed relatively high levels of groundwater flow in the spawning gravel used by chum salmon in these modified areas.

Crazy Johnson Creek, a tributary to the lower Grays River, has not been modified to any large extent. A channel modification project to the Grays River was completed to reduce the risk of the Grays River migrating back into the lower portion of Crazy Johnson Creek.

All self-sustaining population chum population in the lower Columbia have habitat conditions that favor high egg to fry survival. All spawning areas have springs, which promote high water exchange through the redd. The literature suggest that chum often prefer these sites. Second, these sites are located in areas that are not at risk to bed scour. Once eggs are deposited, it is unlikely that they will wash out. Other historical spawning areas in the Lower Columbia River are at a high than historic risk for bed scour and/or sedimentation.

The most concentrated development has occurred with the lower 1/3 of Columbia River tributaries, which overlaps totally with the historic range of chum salmon. Armoring of steam banks and lack of functional side/overflow channels (flood plain connectivity) have increased the risk of egg scour and eliminated side channel habitats which chum salmon have shown a preference for spawning.

Since most of historic chum spawning area in the lower Columbia River tributaries is located in alluvial reaches just below the high gradient transport reach, sediment from upslope activities, such as logging and road building, is deposited in these reaches. The level of fine sediment in gravel is likely higher than historic conditions and above conditions found in properly functioning habitat.

The Columbia River is migration corridor for chum salmon smolts. Historic outmigration flows from the Columbia River have been estimated to be near 500,000 cfs as compared to current estimates of 300,000 cfs or less in most years. In addition, the turbidity during the historic spring peak was likely higher than it is today. Alteration of the migration corridor has increased predator habitat and the predation rates since fish take longer to migrate and are more easily observed by native and non-native predators.

There have been major changes in the estuary habitat of the lower Columbia River. Sherwood et al . 1990 estimated the tide flats, swamps, and wetland in the Columbia River estuary has been reduced by 40% between 1870 and 1970. The Corps of Engineers has created Rice Island from dredge spoils, which has been the primary breeding ground for the largest colony of Caspian terns in the world. Predation on chum salmon is unknown but significant predation by terns does occur on other salmonids.

During periods of low ocean productivity it is likely that only the populations that use most productive freshwater habitats can remain productive.

Gorley Creek, an artificially created spawning channel which supported ~25% of the chum salmon in the Grays River, was lost due to flooding in December 1999. If survival of spawners in the West Fork of the Grays River and in the mainstem is low due to bed scour and sedimentation, the Gorley channel may have contributed up to 50% of the natural production in the Grays River.