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The 1985 kokanee spawning run in the Flathead system was the strongest in five years. Escapement to the Flathead River system was 147,000 fish, including 123,000 in McDonald Creek and an estimated 20,000 in the main stem. Enumeration of spawners and redds in the Flathead River was hindered by high fall flows and early freezing in November. The upstream spawning migration from Flathead Lake began in late August. Schools of kokanee were seen six miles above the lake on September 4. We counted 1,156 redds in Flathead Lake, distributed primarily along the southeastern shore. An unusually high proportion (90 percent) of lakeshore spawning occurred in the zone above minimum pool, where egg mortality is very high because of exposure from drawdown. Escapement to the Swan River was 1,350 fish. Four year old (III+) fish comprised 95 percent of the spawning run in the Flathead system. This continues a five-year trend toward dominance of the III+ year class. The age composition of spawners has varied considerably for the past 15 years. The average size of spawning fish was 365 mm, which is identical to the average size of the parent year class in 1981. One of the goals of managing Flathead kokanee is to produce mature fish 300-330 mm in length. In the main stem Flathead River, pre-emergent survival was 80 percent. Survival in McDonald Creek, unaffected by hydroelectric operations, was 83 percent. Sampling showed few hatched alevins, probably due to unusually cold winter temperatures. Egg survival at Blue Bay, a spawning area on Flathead Lake where redds are concentrated below minimum pool, varied in relation to depth and dissolved oxygen concentration in the substrate. Eggs survived 78 days at 2,880 feet where dissolved oxygen was 5.7 mg/l. Eggs survived 35 days at 2,870 feet where dissolved oxygen concentration averaged 2.9 mg/l. Low dissolved oxygen contributed to poor survival to emergence at all elevations in Blue Ray. Experiments in Skidoo Bay confirmed that survival of eggs above minimum pool depends on redds being wetted by groundwater seeps. After 40 days exposure by drawdown, eggs in groundwater seeps showed 86 percent survival, whereas outside of the groundwater seeps eggs survived less than six days. These results confirm that exposure by drawdown is the primary factor that limits kokanee reproductive success in redds above minimum pool. We surveyed the west and south shoreline of Flathead Lake to locate potential kokanee spawning habitat. We found conditions which could support incubating eggs at two sites in South Ray and two sites on the west shore of the lake. Seven other sites on the west shore were not suitable due to low groundwater discharge or low dissolved oxygen. In all these areas suitable substrate existed only within the drawdown zone. The lake should be drafted earlier in the fall, and filled earlier in the spring to improve recruitment from lakeshore spawning. We conducted creel surveys during 1985, and estimated that anglers caught 192,000 kokanee. Anglers harvested 49,200 fish during the ice fishery in Skidoo Bay, 129,000 fish during the summer fishery on the lake, and 13,800 during the fall river fishery. Estimated fishing pressure for the year exceeded 188,000 angler hours. The abundance of mysid shrimp in Flathead Lake, measured at six index stations, increased to 130/mIf in 1986. My & Is increased tenfold from 1984 to 1985, and about threefold from 1985 to 1986. Monitoring of mysid shrimp and zooplankton populations in Flathead Lake is supplementing an investigation of the growth and survival of juvenile kokanee. Kokanee and mysid shrimp feed primarily on planktonic crustaceans. This work was designed to detect a potential decline in kokanee recruitment or growth brought about by competitive interaction with mysid shrimp. Fluctuation in adult kokanee year class strength is in part attributable to the negative effects of hydroelectric dam operation on reproductive success in the main stem Flathead River and in Flathead Lake. Our results show that egg survival in the river has improved in response to stabilized discharge from Hungry Horse Dam. Drawdown exposure continues to limit egg survival in lakeshore redds. Study of the variability in growth and survival of young-of-the-year fish in Flathead Lake will further the understanding of factors which cause fluctuation in the kokanee population.
Studies of kokanee reproductive success in the Flathead system from 1981 to 1987 have assessed the losses in fish production attributable to hydroelectric operations. We estimated that the Flathead Lake shoreline spawning stock has lost at least 50,000 fish annually, since Kerr Dam was completed in 1938. The Flathead River spawning stock has lost 95,000 spawners annually because of the operations of Hungry Horse Dam. Lakeshore spawning has been adversely affected because Flathead Lake has been drafted to minimum pool during the winter when kokanee eggs are incubating in shallow shoreline redds. Egg mortality from exposure and desiccation of kokanee redds has increased since the mid 1970's. When the lake was drafted more quickly and held longer at minimum pool. Escapement surveys in the early 1950's, and a creel survey in the early 1960's have provided a baseline to which the present escapement levels can be compared, and loss estimated. Main stem Flathead River spawning has also declined since the mid 1970's when fluctuating discharge from Hungry Horse Dam during the spawning and incubation season exposed redds at the river margin and increased mortality. This decline followed an increase in main stem spawning in the late 1950's through the mid 1960's attributable to higher winter water temperature and relatively stable discharge from Hungry Horse Dam. Spawning escapement in the main stem exceeded 300,000 kokanee in the early 1970's as a result. Spawning in spring-influenced sites has comprised 35 percent of the main stem escapement from 1979 to 1986. We took that proportion of the early 1970's escapement (105,000) as the baseline against which to measure historic loss. Agricultural and suburban development has contributed less significantly to degradation of kokanee spawning habitat in the river system and on the Flathead Lake shoreline. Their influence on groundwater quality and substrate composition has limited reproductive success in few sites. Studies of the effects of hydroelectric operations on the reproductive success of kokanee in the Flathead system have been ongoing since 1980. Results of these studies have been published in a series of annual progress reports which are detailed in Appendix G. The reports summarize spawning site inventories and spawning escapement, egg and alevin mortality rates and the mechanisms by which water level fluctuations influence mortality, creel surveys, and investigation of the population dynamics of Flathead kokanee. The Region 1 offices of the Montana Department of Fish, Wildlife and Parks distribute this material to the scientific community and the general public. Until recently, it was considered feasible to recover losses to the Flathead kokanee fishery by enhancing and diversifying natural reproduction. But the establishment of opossum shrimp (M. relicta) in Flathead Lake has reduced the availability of zooplankton forage in the spring and summer, and may reduce the viability of juvenile kokanee. In 1986, research was redirected to quantify this competitive interaction and to investigate artificial means of enhancing the kokanee fishery. The average density of mysid shrimp in Flathead Lake has increased to 108/m2 in 1987, and at some locations density exceeds 500/m2. Mysid grazing pressure has delayed the pulse of zooplankton production in the spring and reduced zooplankton standing crop in the summer. Cladocerans such as Daphnia thorata, the preferred food of kokanee of all ages, are the most markedly affected species. The peak density of D. thorata in the summer has declined from 4.8/liter in 1983 to O.9/liter in 1987. Growth rates of underyearling and yearling kokanee have declined, apparently as a result of the reduction in their food supply. Spawning escapement has also declined, falling from 150,000 in 1985. to 25,000 in 1986, to 600 in 1987. Fry-to-adult survival has declined from 2.5 percent to near zero. The causes of high mortality, and which age-classes are most susceptible, are not completely understood, but the observed decline in juvenile growth rate implicates mysid-induced change in the trophic ecology of Flathead Lake. These biological changes in the Flathead system wi11 delay the formulation of a recovery plan for kokanee. Three scenarios represent the possible alternatives for such a plan. If mysid-induced changes in kokanee survival do not persist, or are limited in scope, we can proceed with enhancement of natural kokanee reproduction. This alternative includes protection of main stem spawning with stable fall and winter discharge from Hungry Horse Dam, and enhancing spawning in other tributaries. If the increase in wild fry mortality is limited, main stem flows can be tailored to optimize production from wild escapement and the kokanee fishery can be supplemented with hatchery-produced fry.
This study was undertaken to assess the effects of the operation of Hungry Horse Dam on the kokanee fishery in the Flathead River system. Studies concerning operation of the dam on the Flathead River aquatic biota began in 1979 and continued to 1982 under Bureau of Reclamation funding. These studies resulted in flow recommendations for the aquatic biota in the main stem Flathead River, below the influence of Hungry Horse Dam on the South Fork. Studies concerned specifically with kokanee salmon have continued under Bonneville Power Administration funding since 1982. This completion report covers the entire study period (September 1979 to June 1985). Major results of this study were: (1) development and refinement of methods to assess hydropower impacts on spawning and incubation success of kokanee; (2) development of a model to predict kokanee year class strength from Flathead River flows; and (3) implementation of flows favorable for successful kokanee reproduction. A monitoring program has been developed which will assess the recovery of the kokanee population as it proceeds, and to recommend management strategies to maintain management goals for the kokanee fishery in the river system.
Koktneesalmon (Oncorhvnchusnerka), the land-locked form of sockeye salmon, were originally introduced to Flathead Lake in 1916. My 1933, kokanee had become established in the lake and provided a popular summer trolling fishery as well as a fall snagging fishery in shoreline areas. Presently, Flathead Lake supports the second highest fishing pressure of any lake or reservoir in Montana (Montana Department of Fish and Game 1976). During 1981-82, the lake provided 168,792 man-days of fishing pressure. Ninety-two percent of the estimated 536,870 fish caught in Flathead Lake in 1981-82 were kokanee salmon. Kokanee also provided forage for bull trout seasonally and year round for lake trout. Kokanee rear to maturity in Flathead Lake, then return to various total grounds to spawn. Spawning occurred in lake outlet streams, springs, larger rivers and lake shoreline areas in suitable but often limited habitat. Shoreline spawning in Flathead Lake was first documented in the mid-1930's. Spawning kokanee were seized from shoreline areas in 1933 and 21,000 cans were processed and packed for distribution to the needy. Stefanich (1953 and 1954) later documented extensive but an unquantified amount of spawning along the shoreline as well as runs in Whitefish River and McDonald Creek in the 1950's. A creel census conducted in 1962-63 determined 11 to 13 percent of the kokanee caught annually were taken during the spawning period (Robbins 1966). During a 1981-82 creel census, less than one percent of the fishermen on Flathead Lake were snagging kokanee (Graham and Fredenberg 1982). The operation of Kerr Dam, located below Flathead Lake on the Flathead River, has altered seasonal fluctuations of Flathead Lake. Lake levels presently remain high during kokanee spawning in November and decline during the incubation and emergence periods. Groundwater plays an important role in embryo and fry survival in redds of shoreline areas exposed by lake drawdown. Stefanich (1954) and Domrose (1968) found live eggs and fry only in shoreline spawning areas wetted by groundwater seeps. Impacts of the operation of Kerr Dam on lakeshore spawning have not been quantified. Recent studies have revealed that operation of Hungry Horse Dam severely impacted successful kokanee spawning and incubation in the Flathead River above Flathead Lake (Graham et al. 1980, McMullin and Graham 1981, Fraley and Graham 1982 and Fraley and McMullin 1983). Flows from Hungry Horse Dam to enhance kokanee reproduction in the river system have been voluntarily met by the Bureau of Reclamation since 1981. In lakeshore spawning areas in other Pacific Northwest systems, spawning habitat for kokanee and sockeye salmon was characterized by seepage or groundwater flow where suitable substrate composition existed (Foerster 1968). Spawning primarily occurred in shallower depths (