Vertical distribution and onshore movement of maturing kokanee were studied by means of extensive gill net sets in Nicola Lake between 1958 and 1961. In late spring of 1959 maturing kokanee were found largely in the upper 30 feet of the lake but gradually dispersed to occupy all depths to 100 feet by mid-summer. A diel vertical migration occurred in which maturing kokanee moved surfaceward during the day and downward at night in 1959. In 1961 the reverse condition was observed wherein kokanee avoided areas of bright illumination during the day but moved surfaceward at night. No effect on vertical distribution of kokanee by extensive and rapid fluctuations of the thermocline, initiated by wind induced seiches, was noted in 1959 or 1961. The 1961 vertical distribution appeared closely associated to light intensity. Seasonal and diel changes in diet were observed in 1959. Chironomid pupae were the dominant food organisms eaten in late spring and summer. Planktonic crustaceans were consumed in greatest numbers in late summer, autumn and spring. Kokanee captured in mid-summer in the surface water (0-25 feet) generally had been feeding on planktonic crustaceans whereas those taken from below 25 feet contained largely chironomid pupae and larvae. Onshore movement of mature kokanee toward a spawning stream was initiated by falling light intensity and intensified by strong onshore winds. Possible mechanisms of location of the spawning stream were investigated. Migration to an inlet spawning stream and movement within the stream were recorded at two traps, one situated at the stream mouth, the other 1000 feet upstream. Movement into the spawning stream occurred only at night and was unaffected by changes in stream temperature and flow. A significant correlation was found between daily number of kokanee entering the stream and strength of onshore winds. Differences in sex ratio of the spawning runs and length of mature kokanee were recorded and possible causal agents discussed. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)-Oregon State University, 1988. / Includes bibliographical references (leaves 74-80). Also available via the Internet.

Several aspects of kokanee (Onchorhynchus nerka) ecology were studied in the fluctuating, 80ha Porcupine Reservoir, Utah in order to determine optimum management strategies. In 1981, escapement was enumerated and estimates of egg deposition were made . An estimate of the resulting fry recruitment was also attempted and was successful up to the arrival of spring runoff. In 1982, escapement was enumerated and estimates of egg deposition were made, with subsequent estimates of egg deposition and percent survival to the advanced eyed stage. Age and growth rates were determined and survival rates estimated. Escapement for 1981 and 1982 was 5,463 and 7,113 kokanee, respectively, depositing an estimated 1,843,955 and 2,393,757 eggs, respectively._ The estimated fry recruitment to the reservoir for the 1981 spawning run was 57,000 fish up to the arrival of spring runoff and appeared to be only a fraction of the total number of fry in the river. From the 1982 spawning run, an estimated 2,265,507 eggs were actually deposited, of these an estimated 64.2% or 1,457,599 eggs were fertilized and survived to the advanced eyed stage. Kokanee growth rates were good. Fish mature and spawn at 34 months of age at an average total length of 364mm. Twelve month old kokanee average 124mm and 24 month old fish 257mm. The kokanee population continues to grow but at a decreasing rate and survival rates are declining. For every kokanee that estimated 8.2 progeny survived to spawn spawned in 1972, an in 1975 and for every spawning kokanee in 1979 an estimated 3.0 progeny survived to spawn in 1982. The kokanee is presently underharvested and appears to be at or near the carrying capacity of the reservoir. In order to acheive an optimum sustainable yield the spawning population should be reduced and maintained at approximately 2,000 fish ( 1,000 redds).

Lake Tahoe kokanee salmon have experienced decreasing mean adult size and fluctuating populations since 1970. We proposed to determine whether fish production was limited by spawning and incubation processes in Taylor Creek , or by growth constraints , or by mortality in the lake by studying egg-to-fry survival rates and early life history . Estimated egg-to-fry survival was 15. 9% for the 1994 brood year and 1.5% for the 1995 brood year. Egg-to-adult survival was 3.5% for the 1991 brood year and 5.9% for the 1992 brood year. Of the 35 possible survival scenarios, egg-to-fry survival was 7.5-20% and fry-to-adult survival (inlake phase) was 20-60%. The differing egg-to-fry survival rates corresponded to different stream temperature regimes during critical incubation periods. During and after the outmigration, fry inhabited the littoral zone, pelagic zone, and an estuarine environment created by a flooded meadow. Chironomids were the dominant prey in both 1995 and 1996 for fry in the littoral regions. Fry declined in the littoral zone approximately 30 days after peak outmigration during both 1995 and 1996. Juveniles and adults in the lake inhabited the upper 10 m of the water column and consumed primarily copepods for most of their limnetic life. Otolith analysis revealed that five year classes were present with the fifth year class representing 15.0% (1995) to 7.6% (1996) of the spawning population. Despite Lake Tahoe's low productivity, kokanee achieved greater size at age-4 than many other populations. Low densities (14.5 fish/hectare) and warmer winter temperatures may enable kokanee to reach greater size. Kokanee production may be limited by warm stream temperatures during spawning and early incubation in some years. Egg-to-fry survival is the most limiting factor. Enhancement of the kokanee population should focus on this phase of life history. Kokanee are not native to the Lake Tahoe Basin, which is considerably south of their historic range. Kokanee may be limited by inadequate adaptation to California's mild climate.

This study tracked the chronology and severity of Myxobolus cerebralis infection and related it to survival of age-0 kokanee to determine whether M. cerebralis represented a significant agent of morality in the population. Environmental conditions and losses to predation were identified and linked to age-0 kokanee survival to identify other sources of mortality in the population. We attempted to track survival of age-0 kokanee from the outmigration into the reservoir until the end of the first growing season in September of each year. The number of age-0 kokanee that entered the reservoir was calculated by obtaining estimates of total egg deposition and egg-to-fry survival for the 1999 brood year. Age-0 kokanee were primarily infected by the parasite after they had entered the reservoir in spring. Prevalence and severity increased rapidly throughout the summer and nearly all age-0 kokanee were infected by August of both years. In total, 495 age-0 kokanee were examined for clinical lesions associated with M. cerebralis in 1999 and 2000, but only one fish displayed a cranial abnormality in 2000. Low survival rates of age-0 kokanee from July through September were observed and coincided with increased prevalence and severity. However, because of high reservoir temperatures, low food levels, predation, and entrainment, evidence for M. cerebralis acting as a direct source of mortality on age-0 kokanee was elusive during our study. In age-1 and older kokanee we did not find any evidence that M. cerebralis had an effect on growth and overall condition of the fish. Infection severity and presence of clinical signs varied between years and were likely more related to limitations of the diagnostic techniques. Any effects that M. cerebralis may have had on kokanee are likely to occur during the first growing season and may impact the host's ability to cope with the other environmental stressors identified at Porcupine Reservoir. Despite high mortality rates, the kokanee population at Porcupine Reservoir was considered to be overabundant based on estimated densities and length distributions of spawning fish. M cerebralis did not appear to have significant effect on the abundance of the kokanee population but we were unable to determine whether or not the parasite was a source of direct mortality because of other potential sources of mortality.

I used incubation baskets containing viable eggs and spawning substrate to estimate the survival to emergence and time of emergence of kokanee salmon Oncorhynchus nerka at depths to 20 m in Flaming Gorge Reservoir, Utah-Wyoming. Traps on the incubation baskets captured fry emerging from a known quantity of eggs. Water drawn into a syringe from an intragravel pipe buried near each incubation basket was used to determine intragravel dissolved oxygen concentrations throughout the intragravel period. Water from control baskets without eggs did not have significantly greater dissolved oxygen concentrations than adjacent water. A jar associated with each incubation basket collected sediment to determine absolute and organic sedimentation during the study. Temperatures at the substrate water interface were used to describe degree-days accumulated before emergence. Survival to emergence ranged from zero to 66% and was most significantly related to mean intragravel dissolved oxygen concentrations. Survival to emergence, mean intragravel dissolved oxygen concentrations , and organic sedimentation decreased with depth.