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Photo by Scott Root
Photo Copyright Scott Root
Sockeye Salmon (Kokanee)
Oncorhynchus nerka
NatureServe conservation status
Global (G-rank): G5
State (S-rank): SNA
- Reason: First introduced in Utah in 1922 and stocked regularly since then. Occurs naturally in northeastern Asia and northwestern North America.
External links
General information
Spending its entire life in freshwater, the kokanee salmon, Oncorhynchus nerka, is a landlocked form of the sockeye salmon. Kokanee salmon are a popular nonnative game fish in Utah; they have been introduced and become established in Flaming Gorge Reservoir, Strawberry Reservoir, and several other water bodies in the state.
Kokanee salmon are silvery-blue for most of their lives, but turn a bright red color in the fall of their last year, prior to spawning. Kokanee salmon spawn over gravel beds, and they will often dig pits (called redds) in the gravel to receive their eggs. Much like sockeye salmon, each kokanee salmon returns to the area of its birth to spawn. Also similar to the sockeye salmon, kokanee salmon live for three to four years and die after spawning is complete. In Utah, kokanee salmon eggs hatch in the spring, usually in April.
The kokanee salmon diet is composed primarily of small animals, with large zooplankton being a food item of choice.
Phenology
Kokanee: feeding generally heaviest from sundown to dark (Sigler and Sigler 1987). Young sockeye feeding heaviest in afternoon, lightest at night and early morning (Pauley et al. 1989).
Species range
During oceanic feeding and maturation, this salmon ranges throughout the North Pacific Ocean, Bering Sea, and eastern Sea of Okhotsk north of 40 degrees north latitude; there is considerable intermingling of Asian and North American populations, and of North American populations from Bering Sea and Gulf of Alaska streams; the range shifts southward for winter, northward during warmer months. Natural lake populations occur in Japan, former USSR, Alaska, Washington, Idaho, Oregon, Yukon, and British Columbia. Anadromous forms occur in Asia from Hokkaido, Japan, to the Anadyr River (spawning mainly on the Kamchatka Peninsula); in North America, anadromous populations range from the Sacramento River, California, north to Point Hope, Alaska (common in north, rare south of Columbia River drainage). Major Alaskan spawning areas are in tributaries and lakes of the Kenai, Chignik, Naknet, Kuichak, Wood, and Kodiak Island river systems. South of Alaska in the Pacific Northwest, the major spawning river is the Fraser River system in British Columbia, with smaller runs in the Baker, Columbia, Cedar, Quinalt, and Ozette rivers in Washington. The Fraser River includes a number of important nursery lakes (Cultus, Adams, Harrison, Horsefly, Shuswap, and Quesnel) and many tributaries that support the major portion of the Pacific Northwest population. In eastern Washington, major nursery lakes for Columbia River are Lake Wenathchee and Osoyoos Lake. In western Washington, major nursery lakes are Quinalt Lake, Ozette Lake, Baker Lake, and Lake Washington. In a 1996 survey of populations in the contiguous U.S., one healthy native stock was identified (Wenatchee River, Washington). The kokanee (lake-stream form) has been introduced in many western states and elsewhere, but most transplants have been unsuccessful in establishing self-sustaining populations.
Migration
Anadromous forms migrate from ocean waters up coastal streams and rivers to spawn in natal waters; spend 1-4 years (usually 2 years) in ocean, 2 years in freshwater; ascend river, spend 1-8 months in lake, then move to natal spawning area. Many non-anadromous populations move from lakes into tributary streams to spawn, some remain in lakes. Enters spawning rivers from late spring to midsummer, depending on the population.
Habitat
Nonbreeding adult sockeye salmon are oceanic, with many occurring in nutrient-rich waters of Alaska and the arctic. Kokanee do best in large, cold, mountain lakes (Sigler and Sigler 1987), where the presence of well-oxygenated water is essential (Sublette et al. 1990).. Water temperatures above 60 degrees F (about 15.5 C) lead to significant mortality, especially among the young (see Sublette et al. 1990). Young are not often found in estuarine or inshore waters after reaching the marine environment (Pauley et al. 1989).Kokanee usually spawn in tributary stream of lake, often in riffle over gravel substrate; sometimes along gravelly shore of lake where seepage outflows, springs, or wind-induced waves occur. Sockeye move up coastal rivers and spawn in streams. Female constructs a redd (several nesting pockets) in gravel (usually) or sand bottom.
Food habits
Kokanee feed on zooplankton. Young sockeye eat primarily planktonic crustaceans. At sea, young sockeye feed on zooplankton, small fishes and insects; as they grow they eat more fish.
Ecology
Life cycle of sockeye similar to kokanee except sockeye matures in the ocean rather than lakes. Kokanee often travels in large schools. (Sigler and Sigler 1987). Two studies each reported survival rate of 4-20% for marine portion of life cycle (see Pauley et al. 1989). Northern squawfish and rainbow trout may be important predators on young in some lakes. Schools of young in lakes disperse as dusk approaches, reform after dawn (Pauley et al. 1989). In Montana, the introduction of opossum shrimp (MYSIS RELICTA) was followed by an abrupt decline in the kokanee population, apparently due to zooplankton decline caused by shrimp predation (Spencer et al. 1991).
Reproductive characteristics
Anadromous forms migrate from ocean waters up coastal streams and rivers to spawn in natal waters. They spend 1-4 years (usually 2 years) in the ocean before ascending streams (mainly in summer but some stocks as early as winter). Many stocks spawn in fall (peak often in October or November), but spawning extends into winter in some areas. Spawning sites often are in gravel riffles, sometimes along gravelly shores of lakes where seepage outflows, springs, or wind-induced waves occur. Eggs hatch in 6-9 weeks, depending on temperature, and larvae emerge 2-3 weeks later. Sockeye fry move upstream or downstream to nursery lakes, where the young spend 1-2 years (up to 3 or rarely 4 years in some areas of Alaska; usually 1 year in British Columbia) before going to sea, usually in spring; some populations use stream areas for rearing and may migrate to the sea soon after emergence. Many non-anadromous (kokanee) populations move from lakes into tributary streams to spawn, though some remain in lakes. They enter spawning streams from late spring to midsummer, depending on the population. Kokanee spawn in different areas from August to February, at temperatures of 40-55 F.
Threats or limiting factors
Decline is due to dams that blocked migration, mainstem passage mortality at Columbia and Snake river dams, overutilization in commercial fisheries, and habitat modification (see Nehlsen et al. 1991). Sockeye in the Deschutes River (Oregon) were largely eradicated by dam construction (small anadromous run is maintained by incidental passage of smolts from a resident kokanee population) (Nehlsen et al. 1991). In the Puget Sound area, decline of the Baker River sockeye population has been attributed to upstream and downstream passage problems as a result of dam construction (Nehlsen et al. 1991). Lake Ozette sockeye run on the Washington coast declined because of logging and overfishing in the 1940s and 1950s (Nehlsen et al. 1991).The decline and persistent low abundance of the Rivers Inlet population in British Columbia apparently was due to poor marine survival, and not due to a decline in juvenile abundance (McKinnell et al. 2001).
References
- Biotics Database. 2005. Utah Division of Wildlife Resources, NatureServe, and the network of Natural Heritage Programs and Conservation Data Centers.
