Red salmon, Kokanee salmon, Blueback salmon, Sockeye
The kokanee salmon (Oncorhynchus nerka), also known as the kokanee trout, little redfish, silver trout, kikanning, Kennerly's salmon, Kennerly's trout, or Walla, is the non-anadromous form of the sockeye salmon (meaning that they do not migrate to the sea, instead living out their entire lives in freshwater). There is some debate as to whether the kokanee and its sea-going relative are separate species; geographic isolation, failure to interbreed, and genetic distinction point toward a recent divergence in the history of the two groups. The divergence most likely occurred around 15,000 years ago when a large ice melt created a series of freshwater lakes and rivers across the northern part of North America. While some members of the salmon and trout family (salmonids) went out to sea (anadromous), others stayed behind in fresh water (non-anadromous). The separation of the sockeye and the kokanee created a unique example of sympatric speciation that is relatively new in evolutionary terms. While they occupy the same areas and habitats during the breeding season, when ocean-going sockeye salmon return to freshwater to spawn, the two populations do not mate with each other in some regions, suggesting speciation.
The name kokanee means "red fish" in the Sinixt Interior Salish language, and "silver trout" in the Okanagan language.
The sockeye salmon is sometimes called red or blueback salmon, due to its color. Sockeye are blue tinged with silver in color while living in the ocean. When they return to spawning grounds, their bodies become red and their heads turn green. Sockeye can be anywhere from 60 to 84 cm (2 ft 0 in – 2 ft 9 in) in length and weigh from 2.3 to 7 kg (5–15 lb). Two distinguishing features are their long, serrated gill rakers that range from 30 to 40 in number, and their lack of a spot on their tail or back.
Kokanee are native to many lakes in the western United States and Canada including Alaska, Washington, Oregon, California and Idaho in the United States and British Columbia and Yukon in Canada. Populations of kokanee are also found in Japan and Russia. Additionally, kokanee have been introduced to many other lakes in the United States including in those states mentioned above as well as in Montana, Wyoming, Nevada, Utah, Colorado, Arizona and New Mexico in the west, as well as in New England, New York and North Carolina in the east. Kokanee have also been introduced to lakes in southern Alberta and Saskatchewan in Canada.
Sockeye salmon use patterns of limnetic feeding behavior, which encompasses vertical movement, schooling, diel feeding chronology, and zooplankton prey selectivity. They can change their position in the water column, timing and length of feeding, school formation, and choice of prey to minimize the likelihood of predation. This also ensures they still get at least the minimum amount of food necessary to survive. All of these behaviors contribute to the survivability, and therefore fitness of the salmon. Depending on location and threat of predation, the levels of aggressive feeding behavior can vary.
Sockeye salmon, unlike other species of Pacific salmon, feed extensively on zooplankton during both freshwater and saltwater life stages. They also tend to feed on small aquatic organisms such as shrimp. Insects and occasionally snails are part of their diets at the juvenile stage.
While size range of kokanee is often lake-specific and depends on many factors, in typical populations the kokanee grows to an average size of 23–30 centimetres (9–12 in) with an average weight of 0.45 kilograms (1 lb). In bodies of water with more favorable conditions it can reach a size of up to 51 centimetres (20 in) and weigh 1.4–2.3 kilograms (3–5 lb). The largest documented kokanee, caught by hand in Lower Arrow Lake in British Columbia in 2015, weighed 5.5 kilograms (12.1 lb). Adult kokanee can be found in open water where the thermocline is around 10 °C (50 °F). They can have anywhere between 29–40 gill rakers. As a fish that inhabits freshwater throughout their lifecycle they are often smaller than their sea-going sockeye relatives, due to less food availability. Size is the most significant morphological distinction between the kokanee and the sockeye, but gill raker count can differ from sockeye salmon as well. The main food source of this fish is plankton. “Kokanee have blue backs and silver sides and unlike other salmon and trout, except chum salmon, sockeye and kokanee lack distinct dark spots on their backs and tail fins. In addition, when compared to other trout, they have finer scales, larger eyes, and deeply forked tail”.
The typical life cycle of the kokanee is similar to that of other salmon. They are born in a stream and migrate down to a lake where they will spend most of their adult lives. Kokanee typically live for four years in a lake before heading back to spawning grounds to spawn and die. However, population longevity can vary between 2–7 years. A kokanee can spawn in a variety of different time periods called runs. Individual populations can have multiple runs associated with the kokanee in a lake and occur from August to February. Some kokanee have been seen spawning in April. The female kokanee creates a nest called a redd. She will lay around 1,000 eggs, depending on food availability. Eggs hatch within 110 days, and the juveniles swim out to the lake.
During spawning, the males turn bright red and develop a humped back and an elongated jaw similar to the male sockeye salmon. Females also don a dark red hue during the breeding season, which also corresponds with the breeding season of sockeye salmon.
Competition with introduced lake trout can lead to a decline in kokanee populations during the summer. Lake trout are predatory and will eat young kokanee. Predation by lake trout accounted for 83 percent of the 88 percent decline in kokanee populations in Lake Chelan, Washington. Other factors such as pollution, habitat loss, and warming global temperatures put the kokanee at risk in some areas.
Some kokanee populations have declined in the US and Canada, while others thrive. The kokanee's status is variable among different locations under the Endangered Species Act. They are listed as threatened in Ozette Lake in Washington State. Other kokanee populations in Washington State have shown genetic distinction, but attempts by the Lake Sammamish Kokanee Work Group to get the Lake Sammamish kokanee listed as a separate species and therefore endangered failed the US Fish and Wildlife criteria to be listed as a distinct species. The current IUCN red list standing of sockeye salmon (Oncohynchus nerka), which does not distinguish kokanee, is of least concern.
Even so, King County, Washington, in partnership with US Fish and Wildlife, has issued conservation measures to save the fish that once numbered in the thousands. As few as 150 fish spawned in 2007–2008 marking a critical need for conservation of the state's kokanee population. Currently, restoration of streams, habitats, hatchery breeding, and a ban on fishing for kokanee has caused an increase in native kokanee populations.
Lakes in Canada have also seen a decline in native kokanee, with numbers dropping from 2,800 fish to just 88 fish in 2007 in the Kluane National Park and Reserve. The park has outlawed fishing of kokanee, and it is illegal to possess a kokanee salmon. Conservation efforts have been largely successful with 4,660 kokanee spawning in the park in 2015. It is unclear as to why the kokanee population crashed in the mid and late 2000s.
