Twenty years ago Mission Creek provided a spawning and rearing environment for 80 - 90% of the tributary spawning Kokanee of Okanagan Lake.
One of the major projects in the Okanagan to help restore Kokanee populations is the Mission Creek Spawning Channel. The channel was developed to restore favorable conditions for Kokanee spawners. Clean gravel and special fencing was installed to direct Kokanee into the best spawning areas. It was hoped that these efforts would increase egg and fry survival rates from 5 % in the wild to 80 % in the channel. To date, the channel has not been as successful as hoped. In 1992, 36,000 Kokanee used the spawning channel, but by 1995 this number dropped to 5,000.
In addition to costly enhancement projects such as the one at Mission Creek, the Province of British Columbia imposed a ban on Kokanee fishing in Okanagan Lake in 1995. Scientists believe that this ban will be in effect until at least the year 2001. To avoid Kokanee over-fishing in nearby lakes, the Province also reduced catch limits from 5 to 2 Kokanee per day on Wood and Kalamalka lakes.
Kokanee reductions in Okanagan Lake
Kokanee populations have been of great interest in the past two decades because many lakes that support them have undergone dramatic losses in Kokanee numbers. Okanagan Lake, British Columbia, Canada, is one of many lakes in which this has happened. Declining numbers are most often noted in the number of Kokanee that spawn each year. It is believed that almost one million Kokanee spawned in Okanagan creeks in the 1970s. This number declined to 101,000 by 1994.
There are a number of factors responsible for the decline in Kokanee numbers. Many of these factors destroy Kokanee spawning habitat. Scientists believe that of all Okanagan spawning habitat that existed 100 years ago, only 10 to 20 % remains today. Declining Kokanee populations are due to:
Over-fishing. It has been suggested that Okanagan Lake has been over-fished to a point where the Kokanee population has dropped, although this is not well documented. Over-fishing has likely played a part in the Kokanee fishery collapse, but it has probably been minimal. In 1988, biologists estimated that over 200,000 Kokanee were caught from Okanagan Lake. Normally this number would be acceptable for a lake the size of Okanagan, but with such limited spawning habitat, this count is considered very high. A similar situation occurred in the west arm of Kootenay Lake during the mid-to-late 1970s. The fishery there was many times larger than that of Okanagan Lake. In a study of the fishery collapse, over-fishing did appear to have a major effect, but several other factors contributed to the decline.
Logging Activities. Logging mainly affects Kokanee populations by impacting their spawning grounds. A number of stream characteristics, important to Kokanee, may be altered due to logging practices:
Stream Modification. Many tributaries (streams) of Okanagan Lake have undergone some form of stream modification in recent decades. For example, the Okanagan River was diked and channeled during the late 1950s in an effort to reduce flooding in the Penticton area. Mission Creek in Kelowna was also channeled for a major portion of its lower reach. This resulted in effective flood control. Stream modification destroys Kokanee spawning habitat in several ways:
Lakeshore Development. Although shore- spawning Kokanee are not well documented, lakeshore modification has likely affected their numbers. The development of lakeshore has resulted in the destruction of spawning beds along it. Man-made beaches and road-building alongside the lake have probably destroyed much of the habitat for shore-spawning Kokanee.
Water Use. The Okanagan Valley relies heavily on water for agricultural and domestic uses. Several streams have significant amounts of water removed for these purposes. In addition, many streams travel through residential areas where storm sewers empty into them. These uses have negatively affected Kokanee spawning habitat:
Mysis relicta. Mysis relicta, commonly referred to as opossum or mysis shrimp, was introduced into Okanagan Lake in 1966. These organisms were introduced in hopes of boosting the productivity of the lake, providing extra forage for game fish and enhancing the fisheries industry. Decisions for the introduction were based on several other North American and northern European lakes that observed increased productivity within a few years after the introduction of Mysis relicta. In the beginning , fish populations rose variably for the lakes, but then began to collapse. Scientists discovered that Mysis relicta is a good prey item for large Kokanee, but not for Kokanee aged less than one year. The shrimps are too large for small Kokanee to handle. The major food source for young Kokanee in Okanagan Lake is a small zooplankton species called Daphnia, otherwise termed the "water flea." Unfortunately, Daphnia is also the pref erred food item for Mysis relicta. This leads to competition for the same food source, but the shrimps are more efficient predators than the Kokanee. They feed during the night, whereas the Kokanee do not, and they have a rapid generation time. The shrimps have few predators and normally inhabit different zones of the lake than the Kokanee. It is unknown if Mysis relicta populations have stabilized in Okanagan Lake. If they continue to rise, the Kokanee population will continue to drop.