Date of Award:

1998

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Department name when degree awarded

Fisheries and Wildlife

Advisor/Chair:

David A. Beauchamp

Abstract

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.

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