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Natural
History
Arrow Lakes is now being fertilized also in the hopes of stimulating the food chain and preserving the trophy rainbow and bull trout stocks for which the Arrow Lake is renowned. Zooplankton Copepod zooplankton with egg sacs
Mysids In 1949, mysid shrimp (Mysis relicta) were introduced into Kootenay Lake as an intermediate food source for rainbow trout as they grew and switched from eating Daphnia (zooplankton) to eating kokanee fry. An increase in the number and size of kokanee in the 1960’s was mistakenly attributed to the introduction of the mysid shrimp, which were thought to be acting as a food source for the kokanee. This resulted in the unfortunate introduction of mysids to hundreds of lakes in North America and Scandinavia. The mysids can be detrimental because, although some are eaten by kokanee, they also compete with the kokanee for plankton, their primary source of food. Mysid shrimp, Mysis relicta
Average annual mysid density in the Upper and Lower Arrow were 32 and 63 individuals per square meter, respectively, while Kootenay Lake had a density of 120 individuals per square meter. Although the mysid shrimp competition did not cause the collapse of the Arrow Lakes ecosystem, it could have been a direct contributor to the decline of the kokanee populations. Fish The Columbia Basin supports 27 native species of fish including rainbow trout, bull trout, kokanee, mountain whitefish, burbot and white sturgeon, as well as a number of smaller fish, some of which are now officially endangered (see Endangered Species). Changes to the physical structure of the system have eliminated the spawning migrations of several of these and caused other changes that have diminished the productive capacity of aquatic systems (see above). Consequently, many of the fish populations are currently in a state of stress (not to say crisis), and this is occupying considerable management attention (see Ecosystem Management). The Columbia and its tributaries contain one of the most distinctive fish faunas in North America (Miller, 1965, in McPhail and Carveth, 1992), all of which probably survived the Pleistocene glaciations (see Earliest Beginnings) somewhere within the Columbia system. Nine Columbia species (35%) are endemic, i.e., they evolved within the system. No other drainage system in British Columbia contains this number of endemic species, and it is these Columbia endemics that set the B.C. freshwater fish fauna apart from that in the rest of Canada (McPhail and Carveth, 1992). Because of the mountainous terrain, there are barriers (falls and rapids) on most upper Columbia tributaries, above which only trout or char occur. In the lower Columbia and Kootenay system, where the gradient lessens, the environment is more benign and the number of species increases until, near the U.S. border, all 27 native species and numerous exotics (see below) are present, either in the main rivers or their tributaries (McPhail and Carveth, 1992). However, the upstream distribution of a number of species of dace and sculpins has been limited by Bonnington Falls, on the Kootenay River below Kootenay Lake, and the 3-5 metre vertical drop where the Pend d'Orielle River enters the Columbia River (McPhail and Carveth, 1992). In addition to the native species, some 16 exotic species (37%) now occur in the Columbia Basin. This is a higher proportion of introduced species than in any other river system in British Columbia (McPhail and Carveth, 1992). Most exotics (brook trout, brown trout, lake trout, broad whitefish, carp, goldfish, tench, brown catfish, black catfish, pumpkin seeds, black crappie, largemouth bass, smallmouth bass, yellow perch and walleye) are found in the lower Columbia and Okanagan drainages. One of these, largemouth bass, has become a sports fish (for example, at Duck Lake in the East Kootenay), but the others are mainly pests, or potential pests. Brief notes on the major sports fish follow: Kokanee (Oncorhynchus merka) Kokanee, landlocked sockeye salmon, are present in large lakes and rivers throughout the Columbia Basin. They have small mouths and eat mainly zooplankton, preferring a diet of about 90% Daphnia. Kokanee feed during the day, hunting their food by sight. They will prey on mysid shrimp if possible, but the mysids feed in the dark and migrate down during the day to where no light penetrates and kokanee can't see them. In their night feedings, mysids are competitors for the limited zooplankton prey. Kokanee are a popular sport fish, and the main prey item for bull trout and large rainbow trout. Kokanee show the first response to a decrease in lake productivity, so their numbers reflect the health of the ecosystem (Ney, 1996). The trend in Kootenay Lake kokanee numbers echoes dam construction, mysid introduction, fertilizer plant operations and lake fertilization, increasing in the1960s when the Kimberley fertilizer plant was fully operational, peaking in the early 1970s, dropping in the 1980s and declining steadily from 1986 to 1991. In 1991 kokanee numbers were about 150 fish per hectare. Research indicated a worsening crisis and convinced scientists and fisheries managers to proceed with fertilization on a trial basis. Since fertilization began in 1992, kokanee numbers have increased to their 1998 population density of 600 - 1000 fish per hectare, totalling 25 - 30 million kokanee in Kootenay Lake. There are roughly five million kokanee in the Arrow Lakes. They are found at depths between five and 35 m and preferably at temperatures between seven and 13.5 degrees C. Bull Trout (Salvelinus confluentus) Formerly called Dolly Varden
trout (actually a char), bull trout are now recognized as
a separate species. A consumate By providing more food (kokanee) for the resident Gerrard rainbow and bull trout populations in Kootenay Lake, fertilization has resulted in larger and more numerous stocks, benefiting the local sports fishery. Overall, both rainbow and bull trout in Kootenay Lake have been increasing by two pounds per year since fertilization began in 1992, with anglers now recording rainbow and bull trout as large as 29 pounds. A similar trend is hoped for in Arrow Lakes. Bull trout raised at the Hill Creek Hatchery are released in Arrow Lakes at the mouths of various creeks. In 1996, for example, 29,077 bull trout were released into Snow, Illecillewaet, Hill and St. Leon Creeks. This program has been scaled back until fertilization has proven successful. Cutthroat Trout (Oncorhynchus clarki lewisi) Isolated populations of Westside cutthroats, a separate subspecies, occupy specific parts of the Columbia drainage. Blocked from migration by impassable falls, they have become so distinct that another species designation, O. c. alpestris, has been proposed (but not widely accepted) for those in the Revelstoke area, such as those in Akokolex Creek (McPhail and Carveth, 1992). Sometime after BC's last Ice Age, they occupied extensive ranges in the Columbia Basin in the absence of vigorous predators (such as bull trout). As the ice melted, the water level dropped, and natural dams, formed by massive ice chunks or terminal moraines, washed out. This isolated certain populations behind falls, while the rest occupied the lower elevation water ways. Later, predators accessed the system from downstream and eliminated all the fish below the falls. Thus, the populations above the falls diverged, evolving to succeed in their unique habitat. Thus, a legacy of variety remains in our native fish species, including unique ones like these relic populations of cutthroat trout. Kootenay Trout Hatchery raises Westslope (Yellowstone) cutthroat trout to stock the area's smaller lakes. In 1996, for example, 33 lakes, primarily in the East Kootenays, were stocked with a total of 119,500 cutthroats for sport fishing. Gerrard Rainbow Trout (a race of Oncohyrnchys mykiss) 22 pound (below) and 15 pound (right) Gerrard Rainbow Trout caught on Arrow Lakes Photos coutesy of Glen Olson Fishing ChartersThe Gerrards, named for an abandoned mining town near their spawning grounds at the outlet of Trout Lake, are a giant race of rainbows that made Kootenay Lake famous for its fishing. However, fishing, nutrient overloading from a fertilizer plant, nutrient starvation because of power dams (Duncan, Libby) and the inappropriate introduction of an exotic crustacean (mysid shrimp) brought them to the edge of extinction, with only a few hundred breeding females observed from the early 1980s and onwards. The Gerrard rainbow trout have responded well to the fertilization of Kootenay Lake, achieving sizes of up to 29 pounds in 1998 and returning to spawn in greater numbers every year. Kootenay Trout Hatchery raises the Gerrard stock to release into smaller lakes in the East and West Kootenays and other parts of BC. In 1996, 16 lakes were stocked with 183,465 Gerrard rainbow trout. That year, a total of 1,002,628 rainbow trout (various stocks) were raised at the Kootenay Trout Hatchery and used to stock 113 different systems. Yellowfin Rainbow Trout (a race of Oncohyrnchys mykiss) The yellowfins, native only to Arrow Lakes, began disappearing soon after construction of the Keenleyside, Mica and Revelstoke dams, apparently having lost spawning habitat and nutrients. An estimated 3,000 adult were lost following dam construction (Pieters et al., 1998). They may be further threatened by the introduction of Gerrard rainbows into Arrow Lakes in the 1980s. These fish were large, up to 14 kg, with distinctive yellow colouration on their bellies, pectoral, pelvic and anal fins (Pieters et al., 1998). According to local anglers, a remnant population remains, yet they have proven elusive to fisheries biologists. Thus, attempts to preserve and enhance the stock have been unsuccessful so far. Burbot or Ling Cod (Lota lota) Ling cod caught on Arrow Lakes
White Sturgeon (Acipenser
transmontanus) White sturgeon are huge, long-lived fish, up to 800 kg in weight and over 100 years old (Cannings, 1993). A resident of large, cool rivers, they formerly occurred in the entire Columbia River, migrating from the ocean to spawn in its upper reaches. Until recently, because of dams, they are only found below Keenleyside Dam below Corra Linn Dam in the Kootenay system. In 1999, however, a small population has been found spawning in the Columbia River below Revelstoke Dam. They formed the basis of a commercial fishery for caviar in the early 1900s, and they still provide excellent eating where it is legal to catch them. They are not known to have spawned in these systems "...since the construction of the hydroelectric dams" altered their spawning habitat (Haas, 1996), and they may be further challenged by toxic chemicals and overfishing. According to Larson, 1998, "...construction and operation of hydropower systems have severely impacted white sturgeon populations in the Columbia River basin. Dams have not only blocked upstream spawning and feeding migrations, but they have also altered and/or destroyed much of the spawning habitat. Dams and their associated reservoirs have also altered food availability, natural flow patterns, and water temperatures." For more information: http://www.worldstar.com/~dlarson/SturgeonoftheColumbia.htm References
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Copyright © Royal
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Suspicions
that something was wrong with Arrow Lakes itself, rather than
the hatchery or some other problem, were fueled by the discovery
that the survival of fry (baby fish) counted migrating out
from the hatchery and again returning as adults was also declining
precipitously (Figure 2, left). This suggested that, once
in the lake, the fish were not getting enough to eat to grow
and to escape their predators. Possible alternative explanations,
such as a marked increase in predator populations or a disease,
were ruled out by intensive research that began in cooperation
with the University of British Columbia, the Ministry of Environment,
Lands and Parks, BC Hydro and Columbia Basin Fish and Wildlife
Compensation Program.
The
entire food chain in lakes is based on algae. The algae found
in the aquatic ecosystem are more technically known as phytoplankton,
meaning plants suspended in water. Phytoplankton are photosynthetic,
meaning they use the energy of the sun to convert carbon dioxide
into high-energy carbohydrates. When consumers graze upon
algae, the energy held in the carbohydrates is transferred
to the consuming animal, which are then consumed by the next
level of the food chain, and the energy is passed on again.
Algae thus provide the energy for all other growth in the
lakes and streams.
Zooplankton
are microscopic animals suspended in water. Zooplankton are
heterotrophic which means they cannot make their own food
and must, therefore, consume plants (herbivores) or animals
(carnivores). Zooplankton are able to move about minimally
to secure food or to migrate diurnally through the water column
(moving up and down daily), occupying both the limnetic zone
where sunlight penetrates and the dark profundal zone. Zooplankton
are consumed in the light-filled limnetic zone by larger zooplankton,
insects, and kokanee, which hunt visually, or in the profundal
zone by crustaceans such as Mysis shrimp, decomposers and
bottom feeders living there.
When
fertilizing, mysid shrimp were an ecological wild card, leaving
scientists unable to predict whether the shrimp would out-compete
the kokanee for the new zooplankton food source expected.
It is now believed that the shrimp graze on the zooplankton
in the productive limnetic layer at night and then migrate
down in the water column during the day where the kokanee
are less able to hunt them. Kokanee hunt by sight in the limnetic
layer during the day. The mysids show no growth trend as of
yet, but they are being carefully monitored lest they suddenly
upset the ecological apple cart.
predator,
bull trout have a large head, sharp teeth, and a relatively
small, narrow body. They are blue-listed in British Columbia
("vulnerable") and are of management concern for
various threats, including logging and hydroelectric development.
For example, an estimated 4,000 adult spawners were lost to
the Revelstoke dam alone (Pieters et al., 1998).
Ling
cod are considered primarily a coarse fish, although they
are sought for food periodically. They are fished by jigging
in ling holes where they swarm in small groups. They have
elongated bodies, brown/yellow colouration and wide flat heads.
Ling are predatory, with a diet consisting mostly of other
fish. Ling cod are common in lakes throughout the Columbia
Basin and all of North America.