Year of Award

2012

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Environmental Studies

Department or School/College

Environmental Studies Program

Committee Chair

Jack Stanford

Commitee Members

Bonnie Ellis, Vicki Watson

Keywords

Alaska, coho, floodplains, ponds, salmon

Abstract

Parafluvial ponds are discrete lentic habitats embedded in the alluvia of gravel bed rivers that are formed by flooding and persist in relation to floodplain geohydrology. On the expansive flood plains of the Kwethluk River, I observed thousands of juvenile salmon apparently trapped by surface disconnection of the ponds from the river. I was interested in whether the salmon could survive until flooding reconnected the ponds to the river. I sampled ponds along the river corridor to describe habitat quantity and juvenile salmon presence, growth, and diet. Furthermore, I looked at pond hydrology, temperature regime, and the role groundwater plays in pond ecology. Total ponds along the river corridor (145km) varied in space and time as the season progressed from spring (n=81), summer (n=166), and fall (n=175) revealing that they were persistent and ubiquitous from the headwaters to the lower river. Five fish species were found, of which three were Pacific salmon, and 51 invertebrate taxa with 15 unique to ponds. Salmon, primarily coho (Oncorhyncus kisutch), were most abundant in ponds. Fish populations ranged from 0 to 772 in the 12 main study ponds. The mean area of ponds was small (44.1m2), but this did not inhibit growth and high survival. Coho consistently fed on small invertebrates, predominantly Chironomids and Cladocera, and growth rates were as high as 1.35mm per week. Not only were fish able to grow, but population estimates were similar throughout the season indicating low mortality, and the annual bimodal occurrence of floods allowed juvenile salmon to actively move in and out of ponds. I concluded that juvenile salmon proactively occupy the shallow environments of parafluvial ponds because they function as nursery habitat that is commonly available on natural floodplain rivers like the Kwethluk.

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© Copyright 2012 Zachary Jon Crete