Kokanee salmon

Kokanee Trout (Oncohynchus nerka)

The kokanee, also known as the little redfish, silver trout, kikanning, silver salmon, 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 and live out their entire lives in freshwater like their Sockeye relatives). 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 divergence recently in the history of the two groups. The divergence most likely occurred around 15000 years ago when a large ice melt created a series of freshwater lakes and rivers across the Northern part of North America connected to the ocean. While some members of the Salmon family (salmonids) went out to sea (anadromous), others stayed behind (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 breeding season (when ocean-going sockeye salmon return), they do not mate with each other in some regions suggesting speciation.

Distribution

Kokanee are found in the Northern US in Alaska, Washington, Idaho, and Oregon up through British Columbia and the Yukon. There are subdivisions of the kokanee found in Japan and Russia as well. The kokanee was introduced to Northeastern states and some Southern States in the US including New England, Montana, North Dakota, Wyoming and to Utah, Nevada and parts of Canada

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Genetic and Morphological Diversity

There is debate as to whether the kokanee has enough genetic distinction to be classified as a subspecies or a separate species from the sockeye. Genetic evidence suggests that the evolution of landlocked Sockeye has occurred more than once with different Kokanee populations showing genetic differences between populations. Most evidence points to events that land-locked the lake-type Sockeye (these sockeye breed in lakes and streams), which evolved into the non-anadromous form. Genetic evidence from Kokanee in the Fraser River Drainage and Columbia River Drainages showed ancestors of the kokanee came from the lake-type sockeye (which spawns in streams and lakes, rather than tributaries like the sea-type Sockeye. This Sockeye is still anadromous and spends most of its adult life out at sea). The data also suggests that the kokanee may have evolved back into its lake-type anadromous form at some point in recent history, although there is a lack of interbreeding between Kokanee and Sockeye in the drainage systems. It is important to note that genetic distinction between sockeye and kokanee that cohabitate the same spawning grounds varies from region to region with some populations showing distinct divergence, while others show very little divergence. Studies done in Okanagan Lake in British Columbia and Lake Sammamish suggested that the genetic diversity between the lake-type sockeye and kokanee marked the divergence of two species as cohabitating Sockeye and Kokanee did not interbreed, although interbreeding was possible to produce viable offspring with characteristics between the kokanee and sockeye parents

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There is some morphological divergence between kokanee and sockeye. The most noticeable difference is size. Kokanee are much smaller than sockeye due to less nutrient availability in freshwater. Other morphological differences include higher gill raker counts in Kokanee, failure to develop the changes that allow Sockeye to transition from fresh to salt back to fresh water, and poor swimming ability compared to sockeye. Kokanee egg size also points to a divergence between Kokanee and Sockeye. Kokanee are considerably smaller than Sockeye and should theoretically have smaller eggs in order to increase fecundity. Instead, egg size varies even though the energetic cost of larger eggs can limit Fecundity of Kokanee populations. Studies have found some physiological differences in the kokanees’ ability to extract carotenoids (that provide red pigmentation during breeding) from food better than sockeye due to sexual selection pressures and mate choice. Again, the degree of morphological variation, such as gill raker count, can vary from population to population.

The Japanese Kokanee, also known as the kunimasu salmon or black kokanee is considered a subspecies of the Sockeye salmon by some and occurs naturally in lakes Akan and Chimikeppu on Hokkaido Island. The creation of a dam caused the extermination of the fish by changing lake acidity and the kokanee was believed to have gone extinct in the 1940s. In 2011 a few fish were found in an isolated lake in Mount Fuji. The Japanese Kokanee varies from its sea-going sockeye relative in a few ways. The Kokanee breeds in March at a depth of 30-40 feet while Sockeye salmon breed in the fall and have a different number of gill rakers than sockeye13. In addition, the black kokanee is much darker in color than the Sockeye or any other Kokanee populations. The fish has been introduced to different lakes around the island for commercial fishing practices. It seems that captive breeding programs for strict commercial use, introduction of non-native Kokanee populations from Canada, and a population crash have decreased the diversity of genetic distinctions between the black kokanee and its sockeye relatives in addition to causing a decrease in native Kokanee populations.

Identification, Life Cycle, and Development

Kokanee grow on average, about 9-12 inches and weight on average 1 pound, but can reach a size of up to 20 inches and weigh 3-5 pounds. The largest Kokanee caught in Washington State weighed 6.25 pounds. Adult Kokanee are found in open water where the thermocline is around 50 degrees Fahrenheit. They can have anywhere between 29-40 gill rakers. As a freshwater-based fish, they are much 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. Spawning 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 will create a nest called a redd. She will lay around 1000 eggs, depending on food availability. Eggs hatch in 110 days and juveniles swim out to the lake. During spawning, the males turn bright red, and develop a humped back and elongated jaw similar to the male Sockeye salmon. Females also dawn a dark red hue during breeding season, which 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% of the 88% 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.

Conservation

Some Kokanee populations have declined in the US and Canada, while other thrive. The Kokanee’s status is variable among different locations under the Endangered species act. They are listed as Endangered in Snake River Idaho and 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 the kokanee is listed under the Sockeye Salmon (Oncohynchus nerka) is of least concern. Even so, King County Washington in partnership with US fish and wildlife has issued conservation measures to save the little red fish that once numbered in the thousands. As few as 150 fish spawn 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 2800 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 4660 kokanee spawning in the park in 2015. It is unclear as to why the kokanee population crashed in the mid and late 2000s.