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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Land/Water Interfaces
DIEL PATTERNS OF EMERGENCE AND RETURN IN A WESTERN OREGON STREAM.
A.M. Farrand1, J.L. Li1, and S.L. Johnson2. 1Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon, 97331, 2USDA Forest Service, PNW Research Station, Corvallis, Oregon, 97331
We examined diel patterns of emergence and return to the stream of several species of mayflies, stoneflies and caddisflies at the H. J. Andrews Experimental Forest in the central Oregon Cascades. From June to September 2001, emergence and pan traps were set continuously along a 100m reach of Lookout Creek. Diel patterns were determined for two twelve-hour periods each week and seasonal patterns were derived by comparing weekly samples. Overall return rates were 25% for caddisflies, 48% for mayflies, and 42% for stoneflies. Overall emergence and return of mayflies and caddisflies were higher at night than during the day, whereas stoneflies were more common in daytime samples. Seasonal trends include an overall decrease in the total numbers of all three orders in both trap types. Densities of birds and spiders, common riparian insectivores, were also estimated. Spider densities increased during the summer and are potentially the dominant consumer of aquatic insects in the riparian zone. Bird numbers remained low throughout the study period.
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