Story and Photography By Barry Bartlett
If kokanee salmon are a key indicator species to the well-being of large aquatic ecosystems in the Columbia Basin, then the health of lakes, reservoirs and spawning tributaries in the region appears to be progressing well.
Hydro-acoustic (sonar) surveys conducted in Arrow Lakes Reservoir, Kootenay Lake, Lake Revelstoke Reservoir and Kinbasket Reservoir estimate that the total abundance of in-lake kokanee increased to nearly 65 million fish in 2002, says Harald Manson, senior fisheries biologist for the Columbia Basin Fish & Wildlife Compensation Program (CBFWCP).
In addition, well over two million kokanee spawners were counted last fall in the Canadian portion of the Columbia and Kootenay River systems. CBFWCP is a joint initiative between BC Hydro and the Ministry of Water, Land & Air Protection (MWLAP) to conserve and enhance fish and wildlife populations in the region affected by the construction of BC Hydro dams.
Manson notes that kokanee, which are landlocked sockeye salmon, are also the primary prey of adult bull trout and rainbow trout and an important food source for burbot and the endangered white sturgeon. For example, Kootenay Lake's world-renowned Gerrard rainbow trout are known to consume upwards of 200 kokanee a year.
Kokanee stocks in Kootenay Lake have recovered to reach a near historic level of 35 million fish in 2002 compared to 21 million in 2001. CBFWCP has been conducting an ongoing experimental fertilization project to restore lake productivity in the North Arm impacted by the impoundment of nutrients behind Duncan Dam.
The fertilization of the North Arm with a mixture of liquid nitrogen and phosphorus was initiated in 1992 after research confirmed the lake was on the verge of an ecosystem collapse and kokanee abundance had declined to an estimated seven million fish. Scientists have been monitoring the water quality to measure ecosystem response to fertilization levels and make adjustments as necessary.
Manson says scientists have learned that the appropriate amount of phosphorus to dispense into the North Arm is around 48 metric tonnes per year.
"Too much phosphorus can cause the growth of undesirable blue-green algae while too little phosphorus results in an insufficient green algae food source for zooplankton to support the target kokanee population of 25-35 million fish."
Kokanee spawning escapement in the North Arm decreased from 595,000 in 2001 to 464,000 in 2002. But with the increase in kokanee abundance to 35 million, biologists are expecting spawner numbers to rebound over the next few years toward the target of 750,000 spawners in the North Arm annually.
The fertilization of the North Arm is having some residual benefits throughout the lake. However, the South Arm, impacted by the construction of Libby Dam in Montana, continues to experience decreased spawning runs with less than a total of 5,000 spawners reported for all streams.
The increase in kokanee abundance from fertilization continues to have a positive impact on the Kootenay Lake sport fishery. Results from the 2001 Kootenay Lake Rainbow Trout Survey conducted for MWLAP - Nelson Fisheries Branch with funding by the Habitat Conservation Trust Fund indicate an increase in trout numbers coinciding with the fertilization program and high rainbow trout harvest rates in the late 1990's.
Kokanee abundance in Arrow Lakes Reservoir remained at the 2001 level of 20 million fish in 2002.
The number of kokanee spawners to the Hill Creek Spawning Channel increased to a nine-year high of 195,000 and compared to 137,000 in 2001.
In addition, an aerial survey conducted on 28 Arrow Lakes Reservoir tributaries totaled about 650,000 spawners.
When the experimental fertilization project was initiated in 1999, in-lake kokanee abundance was estimated at 3-6 million with 90,000 spawners at Hill Creek and 394,500 spawners in 28 Arrow tributaries.
Glen Olson, who operates a fishing charter and conducts creel surveys for CBFWCP on the Arrow Lakes Reservoir, says the 2002 sports fishery was excellent. "Overall, the fishing for rainbow trout and bull trout in 2002 was excellent," says Olson, adding "there were lots of rainbow trout caught that were between 12 and 17 pounds."
While the two experimental fertilization projects are contributing significantly to restoring the Arrow and Kootenay Lake ecosystems, Manson notes that other factors play a vital role as well including the level of natural nutrient loading from tributaries and sunlight at critical times of the year.
The completion of BC Hydro's Mica Dam in 1973 and Revelstoke Dam in 1984 created the Kinbasket and Revelstoke reservoirs. Provincial fisheries managers introduced kokanee to the Kinbasket Reservoir with 366,000 kokanee fry and 257,000 eggs between 1982 and 1985. By 1991 the kokanee population in Kinbasket Reservoir had grown to 2.28 million with another 50,000 colonizing Revelstoke Reservoir, primarily by entrainment through Mica Dam. In 2002, hydro-acoustic surveys estimated kokanee abundance in Kinbasket reached 7.95 million and more than doubled in Revelstoke Reservoir over 2001 to 1.48 million fish.
However, MWLAP Ecosystem Specialist Dale Sebastian, who conducts the annual hydro-acoustic surveys as part of BC Hydro's Large River & Reservoir Sustainability Indexing, suspects high water flows in 2002 led to an entrainment of more kokanee than normal from Kinbasket into Revelstoke Reservoir. He cautions the 1.48 million fish may be more than the reservoir is able to support.
The successful establishment of healthy kokanee populations in Kinbasket and Revelstoke reservoirs is good news to Hugh Smith, BC Hydro's Manager of Environmental & Sustainability Policy and representative on the CBFWCP Steering Committee.
"The construction of dams and creation of reservoirs changed the natural system and impacted water quality, food chains and fish species. With initiatives like the fertilization projects and spawning stream enhancements, these changes are now being addressed," explains Smith.
"But the reservoirs also offer opportunities to establish new food chains which are benefiting species such as rainbow trout and bull trout which were impacted by the dams and, as a by-product, creating new sport fisheries." Smith anticipates the critically-imperiled upper Columbia white sturgeon species will also benefit because kokanee are an important food source for adult sturgeon, particularly the kokanee spawners that die each fall.
Anecdotal information suggests that the sturgeon as well as burbot wait off the mouths of tributaries during spawning runs and feed on spent kokanee as they are washed out of the streams.
An estimated 265,000 kokanee spawners were counted in fall 2002 in an aerial survey of tributary streams to the upper Columbia River and the widely-fluctuating Kinbasket Reservoir. This number is down from 400,000 in 2001 but within the average annual range.
Kokanee spawning escapement in tributary streams to the upper Kootenay River flowing into Koocanusa Reservoir has increased steadily since 1997. The 2002 aerial survey estimated nearly 500,000 spawners in 2002 compared to 385,000 in 2001.
Kokanee were introduced into Lake Koocanusa, created by Libby Dam, in the late 1970's and have developed into an international fishery as well as a primary food source for bull trout. While more than half of the 144-km Lake Koocanusa is in Montana, over 95% of kokanee production occur in tributaries on the B.C. side of the border.
CBFWCP Program Manager Maureen DeHaan says the annual kokanee abundance and spawner surveys are helping to track trends over the long term, identify potential problems and measure the effectiveness of the fertilization projects and spawning tributary enhancements.
Wayne Stetski, WLAP Kootenay Regional Manager and representative on the CBFWCP Steering Committee, notes that the partnership between WLAP and BC Hydro through the Compensation Program is helping the province manage both aquatic and terrestrial ecosystems in the Columbia Basin for the benefit of residents and the fish and wildlife species impacted by BC Hydro dams. CBFWCP is funded $3.2 million annually in perpetuity by BC Hydro. The two fertilization projects are long term and expected to continue as long as the dams impound nutrients.
END NOTE: Barry Bartlett is the Public Communications Coordinator for the Columbia Basin Fish & Wildlife Compensation Program. He’s based in Nelson, British Columbia and can be reached at: barry.bartlett@bchydro.bc.ca
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