Sockeye Salmon

Oncorhynchus nerka

Description

Adult Oncorhynchus nerka (sockeye salmon) are typically bright red, with a green head. During the ocean and adult migratory phase they often have bluish backs and silver sides, giving rise to another common name, "bluebacks." The name "sockeye" is thought to have been a corruption of the Indian word "sukkai."

Behavior

Sockeye salmon exhibit a wide variety of life-history patterns that reflect varying dependency on the freshwater environment. With the exception of certain river-type and sea-type populations, the vast majority of sockeye salmon spawn in or near lakes, where the juveniles rear for one to three years prior to migrating to the ocean. For this reason, the major distribution and abundance of large sockeye salmon stocks are closely related to the location of rivers that have accessible lakes in their watersheds for juvenile rearing.

Growth influences the duration of stay in the nursery lake and is influenced by intra-and inter-specific competition, food supply, water temperature, thermal stratification, migratory movements to avoid predation, lake turbidity, and length of the growing season. Lake residence time usually increases the farther north a nursery lake is located. In Washington and British Columbia, lake residence is normally one or two years, whereas in Alaska some fish may remain three or four years in the nursery lake, prior to smoltification. Adaptation to a greater degree of utilization of lake environments for both adult spawning and juvenile rearing has resulted in the evolution of complex timing for incubation, fry emergence, spawning, and adult take entry that often involves intricate patterns of adult and juvenile migration and orientation not seen in other salmon species.

Upon emergence from the substrate, sockeye salmon alevins exhibit a varied behavior that appears to reflect local adaptations to spawning and rearing habitat. For example, lake-type sockeye salmon juveniles move either downstream or upstream to rearing lakes. Periods of streambank holding are limited for most juvenile sockeye salmon, as emergents in streams above or between connecting lakes use the current to travel to the nursery lake. Predation on migrating sockeye salmon fry varies considerably with spawning location. Sockeye salmon fry mortality due to predation by other fish species and birds can be extensive during downstream and upstream migration to nursery lake habitat, and is only partially reduced by the nocturnal migratory movement of some fry populations. Juveniles emerging in streams downstream from a nursery lake can experience periods of particularly high predation compared with other juvenile sockeye. Juvenile sockeye salmon in lakes are visual predators, feeding on zooplankton and insect larvae. Smolt migration typically occurs between sunset and sunrise, beginning in late April and extending through early July, with southern stocks migrating the earliest. Once in the ocean, sockeye salmon feed on copepods, euphausiids, and amphipod crustaceans, fish larvae, squid, and pteropods. The greatest increase in length is typically in the first year of ocean life, whereas the greatest increase in weight is during the second year.Northward migration of juveniles to the Gulf of Alaska occurs in a band relatively close to shore, and offshore movement of juveniles occurs in late autumn or winter.

Among other Pacific salmon, sockeye salmon prefer cooler ocean conditions. Lake-or river-type will spend from one to four years in the ocean before returning to freshwater to spawn. Adult sock-eye salmon home precisely to their natal stream or lake habitat. Stream fidelity in sockeye salmon ensures that juveniles will encounter a suitable nursery lake.

Habitat

On the Pacific coast, sockeye salmon inhabit riverine, marine, and lake environments from the Columbia River and its tributaries north and west to the Kuskokwim River in western Alaska. There are also sockeye salmon life forms that are non-anadromous, meaning that members of the form spend their entire lives in freshwater. Nonanadromous sockeye salmon in the Pacific Northwest are known as kokanee. Occasionally, a proportion of the juveniles in an anadromous sockeye salmon population will remain in their rearing lake environment throughout life and will be observed in the spawning grounds together with their anadromous siblings. "Residual sockeye" refers to these resident, non-migratory progeny of anadromous sockeye salmon parents.

Among the Pacific salmon, sockeye salmon exhibit the greatest diversity in selection of spawning habitat and great variation in river entry timing and the duration of holding in lakes prior to spawning. The vast majority of sockeye salmon typically spawn in inlet or outlet tributaries of lakes or along the shoreline of lakes where upwelling of oxygenated water through gravel or sand occurs. However, they may also spawn in suitable stream habitat between lakes; along the nursery lakeshore on outwash fans of tributaries or where upwelling occurs along submerged beaches; and along beaches where the gravel or rocky substrate is free of fine sediment and the eggs can be oxygenated by wind-driven water circulation. All of these spawning habitats may be used by the lake-type sockeye salmon.

Sockeye salmon also spawn in main-stem rivers without juvenile lake-rearing habitat. These are referred to as "river-type" and "sea-type" sockeye salmon. In areas where lake-rearing habitat is unavailable or inaccessible, sockeye salmon may utilize river and estuarine habitat for rearing or may forgo an extended freshwater rearing period and migrate to sea as underyearlings. Riverine spawn-ers that rear in rivers for one or two years are termed "river-type" sockeye salmon. Riverine spawners that migrate as fry to sea or to lower river estuaries in the same year, following a brief freshwater rearing period of only a few months, are referred to as "sea-type" sockeye salmon. River-type and sea-type sockeye salmon are common in northern areas and may predominate over lake-type sockeye salmon in some river systems.

Within the range of West Coast sockeye, there often exist populations of resident lake-type nonanadromous sockeye salmon. Non-anadromous sockeye salmon are commonly referred to as "kokanee," whose parents, for several generations back, have spent their whole lives in freshwater. Several native and introduced populations of kokanee within the geographic range of West Coast sockeye salmon may be genetically distinct and reproductively isolated from one another and from other salmon populations. It has long been known that kokanee can produce sea-type young. However, the number of sea-type out-migrants that successfully return as adults is typically quite low.

A portion of the juvenile anadromous sockeye salmon will occasionally remain in their lake rearing environment throughout life and will be observed on the spawning grounds together with their anadromous cohorts. These fish are defined as resident sockeye salmon to indicate that they are the progeny of anadromous sockeye salmon parents, spend their adult life in freshwater, but spawn together with their anadromous siblings.

Distribution and Threats

In considering the ESU (Evolutionarily Significant Units) status of resident forms of sockeye salmon, the key issue is the evaluation of the strength and duration of reproductive isolation between resident and sea-type forms. Many kokanee populations appear to have been strongly isolated from sympatric sockeye salmon populations for long periods of time.

The National Marine Fisheries Service has identified seven evolutionary significant units for the sockeye salmon, and has listed the Ozette Lake ESU as threatened and the Snake River ESU as endangered.

(1) Okanogan River: This ESU consists of sock-eye salmon that return to Lake Osoyoos through the Okanogan River via the Columbia River and spawn primarily in the Canadian section of the Okanogan River above Lake Osoyoos. The Okanogan River sockeye is distinguished by a) the very different rearing conditions encountered by juvenile sockeye salmon in Lake Osoyoos, b) the tendency for a large percentage of 3-year-old returns to the Okanogan population, c) the apparent one-month separation in juvenile run-timing between Okanogan and Wenatchee-origin fish, and d) the adaption of Okanogan River sockeye salmon to much higher temperatures during adult migration in the Okanogan River.

(2) Lake Wenatchee: This ESU consists of sock-eye salmon that return to Lake Wenatchee through the Wenatchee River via the Columbia River and spawn primarily in tributaries above Lake Wenatchee. The Lake Wenatchee sockeye salmon population is distinguished by: a) Very different environmental conditions encountered by sockeye salmon in Lake Wenatchee compared with those in Lake Osoyoos, b) the near absence of 3-year-old sockeye returns to Lake Wenatchee, and c) the apparent one-month separation in juvenile run-timing between Okanogan and Wenatchee-origin fish.

(3) Quinault Lake: This ESU consists of sockeye salmon that return to Quinault Lake and spawn in the main-stem of the upper Quinault River, in tributaries of the upper Quinault River, and in a few small tributaries of Quinault Lake itself. The Quinault Lake sockeye salmon is considered a separate ESU based on its unique life history. Historical estimates ranged between 20,000-250,000 in the 1920s; the five year average 1991 to 1995 is estimated at 32,000 adults.

(4) Baker River: This ESU consists of sockeye salmon that return to the barrier dam and fish trap on the lower Baker River after migrating through the Skagit River. They are trucked to one of three artificial spawning beaches above either one or two dams on the Baker River and are held in these enclosures until spawning. Sockeye salmon in this population enter the Quillayute River in May through September and hold in the Sol Duc River before entering Lake Pleasant, usually in early November, when sufficient water depth is available in Lake Creek. Historical estimates in 1900 were 20,000; the five year average 1991 to 1995 is estimated at 2,700 adults.

(5) Lake Pleasant: Sockeye salmon in this region enter the Quillayute River in May through September and hold in the Sol Duc River before entering Lake Pleasant, usually in early November, when sufficient water depth is available in Lake Creek. Spawning occurs on beaches from late November to early January. Sockeye salmon in Lake Pleasant are smaller than other salmon populations, weighing no more than 3 lbs (1.4 kg). In some brood years, a majority of Lake Pleasant sockeye spend two years in freshwater prior to migrating to sea. In the 1930s, more than 500,000 sockeye fry were released into Lake Pleasant, but these hatchery fish do not seem to have altered the genetic integrity of the wild population. Sockeye escapement to Lake Pleasant was 760-1,500 fish during the early 1960s.

(6) Ozette Lake: Threatened. This ESU consists of sockeye salmon that return to Ozette Lake through the Ozette River and currently spawn primarily in lakeshore upwelling areas in Ozette Lake. Minor spawning may occur below Ozette Lake in the Ozette River or in Coal Creek, a tributary of the Ozette River. Sockeye salmon do not presently spawn in tributary streams to Ozette Lake, although they may have spawned there historically. Genetics, environment, and life history are the primary factors in distinguishing this ESU. Ozette Lake sock-eye salmon are genetically distinct from all other sockeye salmon stocks in the Northwest, and Ozette Lake kokanee are the most genetically distinct salmon stock in the contiguous United States. However, Ozette Lake kokanee are closely allied to several sockeye salmon stocks on Vancouver Island.

Kokanee are very numerous in Ozette Lake and spawn in inlet tributaries, characteristics and the degree of genetic differentiation from other sockeye salmon populations. The distinctive early river-entry timing, protracted adult-run timing, long three-to 10-month lake-residence period prior to spawning, unusually long spawn timing, and genetic differences from other coastal Washington sockeye salmon are important factors in identifying this ESU. In addition, the relative absence of red skin pigmentation and the presence of an olive-green spawning coloration by the majority of the Quinault stock appear to be unique among major sockeye salmon stocks in Washington. Historical records estimate a few thousand sockeye in 1926, and a few hundred in the mid-1960s. The 1992-1996 average escapement was about 700.

Threats to the Ozette Lake ESU: The declines in sockeye salmon are likely the result of a combination of factors, including introduced species, predation, loss of tributary populations, decline in quality of beach-spawning habitat, temporarily unfavorable oceanic conditions, excessive historical harvests, and introduced diseases.

Recent hatchery production in Ozette Lake has been primarily from local stock, with the exception of 120,000 Quinault Lake sockeye salmon juveniles released in 1983. The release of 14,398 kokanee/sockeye salmon hybrids in 1991-1992 may have had deleterious effects on genetic integrity of the ESU because Ozette Lake kokanee are genetically dissimilar to Ozette Lake sockeye salmon. Sockeye salmon on the West Coast of the United States have experienced declines in abundance in the past several decades as a result of natural and human factors. Forestry, agriculture, mining, and urbanization have degraded, simplified, and fragmented habitat. Water diversions for agriculture, flood control, domestic, and hydropower have greatly reduced or eliminated historically accessible habitat. Studies indicate that in most western states, about 80-90% of the historical riparian habitat has been eliminated. Further, it has been estimated that, during the last 200 years, the lower 48 states have lost approximately 53% of all wetlands and the majority of the rest are severely degraded. Washing-ton's and Oregon's wetlands are estimated to have diminished by one-third. Sedimentation from land use activities is recognized as a primary cause of habitat degradation in the range of West Coast sock-eye salmon.

Sockeye salmon have supported important commercial fisheries through much of their range. Harvest restrictions to protect sockeye in the Columbia River basin have reduced harvest rates for these sockeye. Sockeye salmon from the Washington coast and Puget Sound are harvested in Puget Sound and near-shore fisheries targeting larger sockeye populations originating in British Columbia.

Introductions of non-native species and habitat modifications have resulted in increased predator populations in numerous river and lake systems, thereby increasing the level of predation experienced by salmonids. Predation by marine mammals is also of concern in areas experiencing dwindling sockeye run sizes.

Natural climatic conditions have served to exacerbate the problems associated with degraded and altered riverine and estuarine habitats. Persistent drought conditions have reduced the already limited spawning, rearing, and migration habitat. Further, climatic conditions appear to have resulted in decreased ocean productivity which, during more productive periods, may help offset degraded freshwater habitat conditions.

In an attempt to mitigate the loss of habitat, extensive hatchery programs have been implemented throughout the range of sockeye on the West Coast. While some of these programs have been successful in providing fishing opportunities, the impacts of these programs on native, naturally reproducing stocks are not well understood. Competition, genetic introgression, and disease transmission resulting from hatchery introductions may significantly reduce the production and survival of naturally spawned sockeye. Furthermore, collection of native sockeye for hatchery broodstock purposes may result in additional negative impacts to small or dwindling natural populations.

Harbor seals migrate up the Ozette River into Ozette Lake and have been seen feeding on adult sockeye salmon off the spawning beaches in Ozette Lake. The numbers of seals and of salmon taken by each seal is unknown. Seal predation on sockeye salmon at the river mouth and during the salmon's migration up the Ozette River may also be occurring. The upriver migration of harbor seals to feed on adult sockeye occurs commonly in British Columbia, occurring 100 mi (160 km) upriver on the Fraser River at Harrison Lake and up to 200 mi (320 km) inland on the Skeena River. Sockeye migrate up to Ozette Lake in less than 48 hours, and the majority of the adults travel at night. Given the precarious state of West Coast sockeye salmon stocks, including Ozette Lake, any marine mammal predation may have a significant effect on particular stocks, and these effects need to be more fully understood.

Outside the Olympic National Park, virtually the entire watershed of Ozette Lake has been logged. A combination of past overfishing and spawning habitat degradation associated with timber harvest and road building, have been major causes of this stock's decline.

The exotic plant, reed canary grass, has been encroaching on sockeye spawning beaches in Ozette Lake, particularly on the shoreline north of Umbrella Creek, where sockeye spawning has not occurred for several years. This plant survives over-winter submergence in up to 3 ft (1 m) of water and may possibly provide cover for predators of sock-eye salmon fry. Suitable lakeshore spawning habitat for sockeye salmon is reported to be extremely limited in Ozette Lake. High water temperatures in Ozette Lake and River and low water flows in the summer may create a thermal block to migration and influence timing of sockeye migration. Water temperatures in late-July and August in the Ozette River near the lake outlet have exceeded the temperature range over which sockeye are known to migrate.

(7) Snake River: Endangered. The Snake River sockeye salmon shares its spawning habitat, Red-fish Lake, Idaho, with kokanee, which are non-mi-grating sockeye salmon that spend their entire lifespan in the lake. Studies have indicated that kokanee and the sockeye do not interbreed. Adult Snake River sockeye salmon enter the Columbia River in June and July and ascend the river system at the rate of about 13 mi (21 km) per day. Fish do not feed once they enter freshwater, but live off their accumulated body flesh. Those fish that complete their spawning journey usually arrive at Redfish Lake, Idaho, in August, and take four to eight weeks preparing to spawn. During this period the fish develop a reddish orange body color, the females swell with maturing eggs, and the males develop hooked jaws. In October, females construct nests, known as redds, in gravel areas of the eastern shoreline of the lake. Using her tail, the female digs a depression in the gravel and deposits between 50-100 eggs, which are then fertilized by sperm released by the male. The process continues until the female has deposited about 2,000 eggs. The adults die within a few weeks of spawning. The eggs incubate in the redds until April or May, when the young sockeye emerge. They remain in the gravel and feed from attached yolk sacs. After exhausting this food source the young fry swim up from the gravel and begin to feed on plankton.

In late April or early May, after spending one or two years in Redfish Lake, the juvenile sockeye, now known as smolt, begin their migration to the Pacific. While migrating, fish undergo chemical changes that will allow them to survive in a saltwater environment. Those that successfully reach the Pacific disperse widely for one to three years before attempting the return journey to spawn. Snake River sockeye salmon inhabit both salt-and freshwater at different stages of their life histories. Successful reproduction requires loose gravel that can serve for the construction of redds. Juvenile sockeye require unobstructed passage to the ocean and a water flow strong enough to bring them to saltwater in time to coincide with their physiological changes.

Historically, Idaho's sockeye salmon are known from lakes in the Stanley basin of the Salmon River and the Snake River basin. In the Stanley basin they were produced in at least five lakes: Redfish, Alturas, Stanley, Yellow Belly, and Petit. They also spawned in Big Payette Lake on the North Fork Payette River and in Wallowa Lake on the Wallowa River. For centuries sockeye salmon were a staple food resource of the Shoshone and Bannock Indian tribes. In the late 1800s miners and other settlers arrived in the area and began taking sockeye for food. Between 1870 and 1880 several commercial sockeye fisheries operated at Payette Lake, and plans were made to establish a cannery at Redfish Lake. In the early twentieth century construction of dams on the Salmon and Payette Rivers sharply reduced sock-eye salmon in the Snake River basin.

Today the Snake River sockeye salmon is almost extinct in the wild. Only Redfish Lake has supported a spawning sockeye population and the number of fish returning in recent years has steadily approached zero. Access to other lakes in the Stanley basin which have supported the sockeye in the past have been blocked by irrigation diversions and fish barriers. The Sunbeam Dam, which initially blocked access to the Stanley basin lakes in 1913, was partially removed in 1934 and sockeye populations began to recover. By 1942, 200 sockeye spawned in Redfish Lake. The population increased yearly and reached a peak of almost 4,500 in 1955.

However, the construction of a series of hydropower dams on the lower Snake River in the 1960s created additional obstacles to migration and the population began a steady decline. By 1989 only two fish returned to Redfish Lake. None were seen the following year and in 1991 only four fish returned.

Threats to the Snake River ESU: While many factors have contributed to the decline in the Snake River sockeye salmon, including predation, drought, and overharvesting, the overwhelming threat to this race of salmon, as for all Pacific Northwest salmon, is the network of hydroelectric dams and irrigation projects that has obstructed the fishes' passage and disrupted the historic pattern of spring water flows. Out-migrating juveniles must deal with eight hydropower dams along the lower Snake and Columbia Rivers. Studies have found that 77-96% of migrating juveniles die on their voyage to the ocean. Upstream-migrating adults also face high mortality because of the dams; between 34-57% percent of adults never reach their spawning ground.

Conservation and Recovery

Although there have been a number of attempts to institute a program to conserve Pacific coast salmon and steelhead, the most comprehensive was mandated by the Pacific Northwest Electric Power Planning and Conservation Act of 1980. This federal law established the Northwest Power Planning Council, which in turn developed a Fish and Wildlife Program with provisions to conserve the Snake River sockeye and other salmon runs. Conservation methods, which involved increased spring water releases from the dams, have met with only limited success, mainly because the timing and amount of releases are not mandated and have been resisted by hydropower producers, who would have to forgo some electrical generation. Attempts to capture juvenile sockeye and transport them around the dams have failed because most have died from the stresses of handling, transport, and overcrowding.

Most experts believe that the only way to promote the recovery of the Snake River sockeye and other threatened salmon runs is to greatly speed up water flow during the spring migration. This would require the drawing down of reservoirs behind the four lower Snake River dams: Lower Granite, Little Goose, Lower Monumental, and Ice Harbor. Water dedicated to salmon conservation would then be used to replenish the reservoirs. This long-term solution would involve the modification of existing fish passage facilities and, since it would also require changes in irrigation practices, river transportation, and patterns of recreational use such as boating and fishing, would encounter significant political opposition and require a lengthy phase-in period. And perhaps more importantly, any change in operation of the hydro-electric dams could affect the production and pricing of electricity in the region.

In the short term, while these issues are being debated, efforts to conserve the Snake River salmon will involve the production of hatchery-spawned fish and strategies to increase the spring flow from available sources. The Idaho Department of Fish and Game and the Shoshone-Bannock Indian tribes, with funding from the Bonneville Power Administration, has begun a hatchery program to increase sockeye production. Young sockeye from Redfish Lake have been trapped and placed in a hatchery. The only female in the group of four fish that returned to the lake in 1991 was captured to conserve the genetic traits of the wild sockeye in hatchery-raised fish.

While the extremely low number of Snake River sockeye have led many researchers to conclude that the run is functionally extinct already, they hope that conservation policies and methods developed for this species will help preserve other imperiled Pacific salmon runs in the future. Researchers have recently identified 101 Pacific salmon runs that they regard as at "high risk of extinction" and another 58 runs that are at "moderate risk."

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

Bjornn, T. C., D. R. Craddock, and D. R. Corley.1968. "Migration and Survival of Redfish Lake, Idaho, Sockeye Salmon, Oncorhynchus nerka." Transactions of the American Fisheries Society 37: 360-373.

Chapman, D. W., et al. 1990. "Status of Snake River Sockeye Salmon." Final Report for Pacific Northwest Utilities Conference Committee. 101 SW Main Street, Suite 810, Portland, Oregon 97204.

National Marine Fisheries Service. 20 November 1991. "Endangered Status for Snake River Sock-eye Salmon." Federal Register 56(224): 58619.

National Marine Fisheries Service. 28 December 1993. "Designated Critical Habitat: Snake River Sockeye Salmon, Snake River Spring/Summer Run Chinook Salmon, and Snake River Fall Chinook Salmon." Federal Register 58(247): 68543.

National Marine Fisheries Service. 10 March 1998."Proposed Threatened Status for Ozette Lake and Designated Critical Habitat for Ozette Lake, Washington Sockeye Salmon." Federal Register 63(46): 11750.

National Marine Fisheries Service. 25 March 1999."Threatened Status for Ozette Lake Sockeye Salmon in Washington."Federal Register 64(57): 14528.

Nehlson, W., J. E. Williams, and J. A. Lichatowich.1991. "Pacific Salmon at the Crossroads: Stocks at Risk from California, Oregon, Idaho, and Washington." Fisheries 16 (2):4-21.