HR: 1340h
AN: H53B-0469    [Abstracts]
TI: Boulder Clusters as Flow Refugia for Juvenile Salmonids and Aquatic Invertebrates in Steep Mountain Streams, Klamath Mountains, Northern California
AU: * Cover, M R
EM: mcover@nature.berkeley.edu
AF: Department of Environmental Science, Policy, & Management. University of California, Berkeley. , 137 Mulford Hall, Berkeley, CA 94720-3114 United States
AU: May, C L
H53B-0469 AF: Department of Earth and Planetary Science. University of California, Berkeley., 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Dietrich, W E
H53B-0469 AF: Department of Earth and Planetary Science. University of California, Berkeley., 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Resh, V H
H53B-0469 AF: Department of Environmental Science, Policy, & Management. University of California, Berkeley. , 137 Mulford Hall, Berkeley, CA 94720-3114 United States
AB: The availability of flow refugia and cover is an important factor affecting habitat suitability for fish and invertebrates, especially in steep, turbulent streams. In some channels, crevices beneath and between large rocks may be the only available flow refugia that allow rainbow trout (Oncorhynchus mykiss) to conserve energy and escape from high velocity flow during large storm events. Many aquatic invertebrates, especially large or crawling taxa, require cover that is provided by unembedded crevice space underneath large stones. To investigate the influence of channel type on habitat availability, we performed intensive surveys of crevice habitat for salmonids and benthic invertebrates in 12 reaches in Walker Creek, a 25 square km basin in the Klamath Mountains of Northern California. We identified four reaches in each of three channel types: plane bed (3.1% - 3.7% slope), step-pool (5.4% - 6.5% slope), and cascade (6.3% - 8.5% slope). We used 4 realistic fish models (5, 10, 15, and 20 cm length) to assess the size of crevices and presence of flow refugia associated with all cobble (64 - 256 mm) and boulder (> 256 mm) grains within five 0.5 m-wide diagonal transects. The total abundance of crevices was similar among plane bed (6.3 +/- 1.1 m-2) (Mean +/- SD), step-pool (6.2 +/- 0.25 m-2), and cascade (6.7 +/- 1.2 m-2) reaches. Small (5 cm) crevices made up the majority of crevices in all three reach types. While the presence of 5 cm and 10 cm crevices was not significantly different between the three channel types, there were significantly more large (20 cm) crevices in cascade (0.73 +/- 0.33 m-2) and step-pool (0.68 +/- 0.1 m-2) reaches than in plane bed (0.26 +/- 0.14 m-2) reaches (AVOVA, p < 0.05). Moderately sized (15 cm) crevices were more common in step-pool reaches (0.91 +/- 0.13 m-2) than either cascade (0.54 +/- 0.15 m-2) or plane bed (0.42 +/- 0.13 m-2) reaches. Based on these results we conclude that step-pool reaches provide the most favorable habitat for larger (15 to 20 cm) fish, probably due to the channel-spawning clusters of large cobbles and boulders that define this channel type. Understanding the processes that develop and maintain these open-framework clusters is important for basin-scale assessment of potential aquatic habitat.
UR: http://nature.berkeley.edu/~mcover
DE: 0408 Benthic processes (4804)
DE: 0483 Riparian systems (0744, 1856)
DE: 1813 Eco-hydrology
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: Fall Meeting 2005