Date of Award:

5-2002

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Department name when degree awarded

Fisheries and Wildlife

Committee Chair(s)

David A. Beauchamp

Committee

David A. Beauchamp

Abstract

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.

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