Chum Salmon

Oncorhynchus keta

Description

Chum salmon belong to the family Salmonidae and are one of eight species of Pacific salmonids in the genus Oncorhynchus. Chum salmon grow to be among the largest of Pacific salmon, second only to chinook salmon in adult size, with individuals reported up to 42 lbs (19 kg) in weight. Average size for the species is around 8-15 lbs (3.6-6.8 kg). Chum salmon are semelparous (they spawn only once and then die). They spawn in freshwater, and exhibit obligatory anadromy (adults migrate from the ocean to freshwater streams to spawn and die), as there are no recorded landlocked or naturalized freshwater populations. The chum salmon is best known for the canine-like fangs and striking body color of spawning males: a calico pattern, with the anterior two-thirds of the flank marked by a bold, jagged, reddish line and the posterior third by a jagged black line. Females are less flamboyantly colored and lack the extreme dentition of the males.

Behavior

Chum salmon usually spawn in coastal streams. Juveniles out-migrate to seawater almost immediately after emerging from the gravel that covers their redd (spawning bed). This ocean-type migratory behavior contrasts with the stream-type behavior of coastal cutthroat trout, steelhead, coho salmon, and most types of chinook and sockeye salmon, which usually migrate to sea at a larger size, after months or years of freshwater rearing. This means that survival and growth in juvenile chum salmon depend less on freshwater conditions than on favorable estuarine and marine conditions.

Another behavioral difference between chum other salmon that rear extensively in freshwater is that chum salmon form schools, presumably to reduce predation, especially if their movements are synchronized to swamp predators. Age at maturity appears to follow a latitudinal trend, in which a greater number of older fish occur in the northern portion of the range.

Age at maturity has been investigated in many studies, and in both Asia and North America it appears that most chum salmon mature between three and five years of age, with 60-90% of the fish maturing at four years of age. However, a higher proportion of five-year-old fish occurs in the north, and a higher proportion of three-year-old fish occurs in the south: British Columbia, Washington, Oregon.

Habitat

Chum salmon usually spawn in the lower reaches of rivers typically within 60 mi (96 km) of the ocean. Redds are usually dug in the mainstream or in side channels of rivers. In some areas, particularly in Alaska and northern Asia, they typically spawn where upwelling groundwater percolates through the redds.

Chum salmon are believed to spawn primarily in the lower reaches of rivers because they usually show little persistence in surmounting river blockages and low falls. However, in some systems, such as the Skagit River in Washington, chum salmon routinely migrate over long distances upstream, as far as 100 mi (160 km). In two other rivers, the species swims a much greater distance. In the Yukon River, Alaska, and the Amur River, between China and Russia, chum salmon migrate more than 1,500 mi (2,400 km) inland. Although these distances are impressive, both of these rivers have low gradients and are without extensive falls or other blockages to migration. In the Columbia River basin, there are reports that chum salmon may historically have spawned in the Umatilla and Walla Walla Rivers, more than 180 mi (288 km) from the sea. However, these fish would have had to pass Celilo Falls, a web of rapids and cascades, which presumably were passable by chum salmon only at high water flows.

During the spawning migration, adult chum salmon enter natal river systems from June to March, depending on characteristics of the population or geographic location. Groups of fish entering a river system at particular times or seasons are often identified by the season in which they "run," and run timing has long been used by the fishing community to distinguish sea-run populations of salmon, steelhead, and sea-run cutthroat trout. In Washington, a variety of seasonal runs of chum salmon are recognized, including summer, fall, and winter-run populations. Fall-run chum predominate, but summer runs are found in Hood Canal, the Strait of Juan de Fuca, and in southern Puget Sound. Only two rivers have chum returning so late in the sason that they are designated as winter-run, and both of these are in southern Puget Sound. Adult chum salmon spend their time feeding at sea. However, not much is known about this pelagic stage of their life history.

Distribution

Chum salmon have the widest natural geographic and spawning distribution of any Pacific salmonid. This is primarily because its range extends farther along the shores of the Arctic Ocean than that of the other salmonids. Chum salmon have been documented to spawn from Korea and the Japanese island of Honshu, east around the rim of the North Pacific Ocean, to Monterey Bay in southern California. The range in the Arctic Ocean extends from the Laptev Sea in Russia to the Mackenzie River in Canada. Historically, chum salmon were distributed throughout the coastal regions of western Canada and the United States as far south as Monterey, California. Presently, major spawning populations are found only as far south as Tillamook Bay on the northern Oregon coast.

Chum salmon may historically have been the most abundant of all salmonids. Prior to the 1940s, chum salmon comprised almost 50% of all salmonids in the Pacific Ocean.

The National Marine Fisheries Service has identified four genetically distinct populations of chum salmon (or Evolutionarily Significant Units; ESU). Two of the four are listed as threatened: Hood Canal summer-run chum and Columbia River chum. The other two populations (Puget Sound/Strait of Georgia and Pacific Coast) are distinct populations but are not considered in danger of extinction.

Puget Sound/Strait of Georgia ESU: Not threatened: The Puget Sound/Strait of Georgia ESU includes most U.S. populations of chum salmon outside Alaska. It includes all chum salmon populations from Puget Sound and the Strait of Juan de Fuca. This region also includes Canadian populations from streams draining into the Strait of Georgia. Chum salmon from the west coast of Vancouver Island are not considered part of this ESU, in part because available genetic information suggests these fish are distinct from Puget Sound/Strait of Georgia fish. Chum salmon populations in the Puget Sound/Strait of Georgia ESU have four recognized summer-run populations and two recognized winter-run populations.

Pacific Coast ESU: Not threatened: This region includes all natural chum salmon populations from the Pacific coasts of Washington and Oregon, as well as populations in the Strait of Juan de Fuca west of the Elwha River. This ESU is defined primarily on the basis of life-history and genetic information. Coastal populations form a coherent group that show consistent differences between other fall-run populations in Washington and British Columbia.

The spawning escapements for this population appear to be increasing, to about 35,000 spawners on the Washington coast. The harvest of chum salmon from coastal fisheries combined had averaged 96,000 fish per year from 1988-1992. This suggests a total abundance level on the order of 150,000 adults.

Hood Canal Summer-Run ESU: Threatened: This ESU includes summer-run chum salmon populations in Hood Canal in Puget Sound and in Discovery and Sequim Bays on the Strait of Juan de Fuca. It may also include summer-run fish in the Dungeness River, but the existence of that run is uncertain. Distinctive life-history and genetic traits are the most important factors in identifying this ESU.

Hood Canal summer-run chum salmon spawn from mid-September to mid-October. Fall-run chum salmon spawn from November through December or January. Run timing data from as early as 1913 indicated temporal separation between summer and fall chum salmon in Hood Canal, and recent spawning surveys show that this temporal separation still exists. Genetic data indicate strong and long-standing reproductive isolation between chum salmon in this population and other chum salmon populations in the United States and British Columbia. Hood Canal is also geographically separated from other areas of Puget Sound, the Strait of Georgia, and the Pacific Coast.

In general, summer-run chum salmon are most abundant in the northern part of the range, where they spawn in the mainstreams of rivers. Farther south, water temperatures and stream flows during late summer and early fall become unfavorable for salmonids. These conditions do not improve until the arrival of fall rains in late October/November. Presumably for these reasons, few summer chum populations are recognized south of northern British Columbia. Summer-run chum salmon populations from Washington must return to fresh water and spawn during periods of peak high water temperature, suggesting an adaptation to specialized environmental conditions that allow this life-history strategy to persist in an otherwise inhospitable environment. Therefore, these populations contribute substantially to the ecological/genetic diversity of the species as a whole.

Genetic data indicate that summer-run populations from Hood Canal and the Strait of Juan de Fuca are part of a much more ancient lineage than summer-run chum salmon in southern Puget Sound.

Although summer-run chum salmon in this region have experienced a steady decline since the late-1960s, escapement in 1995-96 increased dramatically in some streams. Spawning escapement of summer-run chum salmon in Hood Canal numbered over 40,000 fish in 1968, but was reduced to only 173 fish in 1989. In 1991, only seven of 12 streams that historically contained spawning runs of summer-run chum salmon still had escapements. Then in 1995-96, escapement increased to more than 21,000 fish in northern Hood Canal, the largest run since the late 1960s.

Summer runs of chum salmon in the Strait of Juan de Fuca did not demonstrate the marked declining trend that has characterized the summer-run populations in Hood Canal in recent years, although they are at very low population levels. Further, though escapement of summer-run chum salmon to Salmon Creek increased in 1996, the other two populations in the Strait of Juan de Fuca did not show similar increases, and the overall trend in the strait populations was one of continued decline.

Of the 12 streams in Hood Canal that had supported spawning populations of summer chum salmon in recent times, five may have become extinct by 1994, and six of the remaining seven showed strong downward trends in abundance. However, in 1995 and 1996, new information demonstrated substantial increases of returning summer chum to some streams. Several factors may have contributed to the dramatic increase in abundance, including hatchery supplementation, reduction in harvest rate, increase in marine survival, and improvements in freshwater habitat.

Columbia River ESU: Threatened Historically, chum salmon were abundant in the lower reaches of the Columbia River and may have spawned as far upstream as the Walla Walla River, over 300 mi (480 km) inland. Only remnant chum salmon populations still exist in the lower Columbia River. They are few in number, low in abundance, and of uncertain stocking history. Genetic data are available for only two small Columbia River populations, which differ substantially from each other as well as from all other chum populations.

During the first half of the twentieth century, commercial fishers harvested as many as 500,000 chum salmon a year. Today, there may be a few thousand, perhaps up to 10,000, chum spawning annually in the Columbia River basin. The chum salmon run size in the Columbia River has been relatively stable since the run collapsed in the mid-1950s. The minimal run size in 1995 was 1,500 adult fish.

Threats

The present depressed condition of many populations of naturally reproducing chum salmon throughout its range is the result of habitat degradation, water diversions, excessive harvesting, and artificial propagation. These factors exacerbate the adverse affects of competition, predation, drought and poor ocean conditions. Habitat modification is a large factor that affects the chum salmon.

Chum salmon depend less on freshwater habitats than some other Pacific salmonids. However, their spawning areas still extend up to 50 miles (80 km) upstream in many rivers, and their requirements for successful spawning and rearing, such as cold, clean water and relatively sediment-free spawning gravel, are similar to those of other Pacific salmon.

Alterations and loss of freshwater habitat for salmonids have been extensively documented in many regions, especially in urban areas or habitat associated with construction of large dams. Since about 1975, a major issue in stream restoration has been the role that large woody debris plays in creating and maintaining Pacific salmon spawning and rearing habitat. Descriptions of pre-development conditions of rivers in Washington and Oregon that had abundant salmonid populations suggest that even big rivers had large amounts of instream woody debris. This debris not only blocked most rivers to navigation, but also contributed to trapping sediments and nutrients, impounding water, and creating many side channels and sloughs. Many streams consisted of a network of sloughs, islands, and beaver ponds with no main channel. For example, portions of the Willamette River reportedly flowed in five separate channels, and many coastal Oregon rivers were so filled with logjams and snags they could not be ascended by early explorers.

Besides clearing rivers for navigation, extensive stream improvements were accomplished to facilitate log drives. Historically, some of the more adverse impacts on the estuarine and freshwater habitats used by chum salmon resulted from stream improvements in the 1800s and early 1900s, when logs were transported down streams and stored in main stems of rivers, lakes, and estuaries. These activities included blocking off sloughs and swamps to keep logs in the mainstream and clearing boulders, trees, logs, and snags from the main channel. Smaller streams required the building of splash dams to provide sufficient water to carry logs. Scouring, widening, and unloading of main-channel gravel during the log drive may have caused as much damage as the initial stream cleaning. Stream cleaning continued through the mid-1970s in many areas not only for flood control and navigation, but also as a fisheries enhancement tool. Debris in streams was viewed as something that would either impede or block fish passage and as a source of channel destruction by scour during storm-induced log-jam failures.

Stream modification with the most impacts on chum salmon are: (1) Water withdrawal, conveyance, storage, and flood control, resulting in insufficient flows, stranding, juvenile entrainment, and instream temperature increases; (2) logging and agriculture leading to the loss of woody debris, sedimentation, loss of riparian vegetation, habitat simplification; (3) mining, especially gravel removal, dredging, pollution; and (4) urbanization leading to stream channelization, increased runoff, pollution, habitat simplification.

Chum salmon generally spend only a short time relative to other salmonids in streams and rivers before migrating downstream to estuarine and nearshore marine habitats. Because of this, the survival of early life history stages depends more on the health and ecological integrity of estuaries and nearshore environments than it does for most other Pacific salmon. Another facotor that effects the survival of the chum salmon is harvest.

Incidental harvest in salmon fisheries in the Strait of Juan de Fuca and coho salmon fisheries in Hood Canal pose a significant threat for the Hood Canal summer-run ESU. Historically, summer chum salmon have not been a primary fishery target in Hood Canal, as harvests have focused on chinook, coho, and fall chum salmon. However, summer chum salmon have a run timing that overlaps with those of chinook and coho salmon, and they have been incidentally harvested in fisheries directed at those species. Prior to 1974, Hood Canal was designated a commercial salmon fishing preserve, with the only net fisheries in Hood Canal occurring on the aboriginal Skokomish Reservation. In 1974, commercial fisheries were opened in Hood Canal, and incidental harvest rates on summer chum salmon began to increase rapidly. By the late 1970s, incidental harvest rates had increased to 50-80% in most of Hood Canal.

Exploitation rates on summer-run chum salmon in Hood Canal have been greatly reduced since 1991 as a result of closures of the coho salmon fishery and of efforts to reduce the harvest of summer chum salmon. Between 1991 and 1996, harvests removed an average of 2.5% of the summer-run chum salmon returning to Hood Canal, compared with an average of 71% in the period from 1980-1989.

The Columbia River historically contained large runs of chum salmon that supported a substantial commercial fishery in the first half of this century. These landings represented a harvest of more than 500,000 chum salmon in some years. There are presently neither recreational nor directed commercial fisheries for chum salmon in the Columbia River, although some chum salmon are taken incidentally in the gill-net fisheries for coho and chinook salmon and there has been minor recreational harvest in some tributaries.

Predation by juvenile coho salmon is a primary another cause of mortality to chum salmon. Artificial propagation is another threat to the chum salmon.

For almost 100 years, hatcheries in the U.S. Pacific Northwest have produced chum salmon for the purpose of increasing the harvest and rebuilding depleted runs. Potential problems associated with hatchery programs include genetic alteration of indigenous, naturally reproducing populations, disease transmission, predation of wild fish, difficulty in determining wild stock status due to incomplete marking of hatchery fish, depletion of wild stock to increase brood stock, and replacement rather than supplementation of wild stocks through competition and continued annual introduction of hatchery fish. All things being equal, the more hatchery fish that are released, the more likely natural populations are to be impacted by hatchery fish. Similarly, the more genetically similar hatchery fish are to natural populations they spawn with, the less change there will be in the genetic makeup of future generations in the natural population.

Conservation and Recovery

The Northwest Forest Plan is a federal interagency cooperative program to coordinate ecosystem management strategy for federal lands administered by the U. S. Forest Service and Bureau of Land Management within the range of the Northern spotted owl, which overlaps considerably with the range of chum salmon.

The most significant element of the Northwest Forest Plan for ocean-run fish is an aquatic ecosystem conservation strategy that includes special land allocations, such as key watersheds and riparian reserves, to provide aquatic habitat refuge; and new watershed analysis, watershed restoration, and monitoring processes.

Several state conservation plans will also benefit the chum salmon: the Washington Wild Stock Restoration Initiative, which implements plans to monitor and evaluate critical populations of salmon and steelheads; Washington Wild Salmonid Policy, which provides habitat protection principles, escapement objectives, harvest management, and genetic conservation for all state agencies; and the Hood Canal/Strait of Juan de Fuca Chum Salmon Conservation Plan.

Exploitation rates on summer-run chum salmon in Hood Canal have been greatly reduced since 1991 as a result of closures of the coho salmon fishery and of efforts to reduce the harvest of summer chum salmon. Between 1991-1996, harvests removed an average of 2.5% of the summer-run chum salmon returning to Hood Canal, compared with an average of 71% in the period from 1980-1989. The harvest restrictions have included an array of specific measures endorsed by both state and tribal fisheries managers, including area closures, restrictions in the duration and timing of chinook and coho salmon fisheries, mesh size restrictions and live-release requirements in net fisheries, catch-and-release requirements for recreational fisheries, and selective gear fisheries that should minimize impacts to summer chum salmon.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

National Marine Fisheries Service. March 10, 1998."Proposed Threatened Status and Designated Critical Habitat for Hood Canal Summer-Run Chum Salmon and Columbia River Chum Salmon." Federal Register 63(46): 11774.

National Marine Fisheries Service. March 25, 1999."Threatened Status for Two ESUs of Chum Salmon in Washington and Oregon." Federal Register 64(57): 14508.

U.S. Fish and Wildlife Service. 2 August 1999. "Endangered and Threatened Wildlife and Plants; Listing of Nine Evolutionarily Significant Units of Chinook Salmon, Chum Salmon, Sockeye Salmon, and Steelhead." Federal Register 64(147): 41835-41839.