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The study objective was to investigate the response of salmonid populations to disturbance in Oregon Coast Range streams in two rock types, basalt and sandstone. Salmonid abundance was estimated in a total of 30 km of channel in 10 Oregon Coast Range streams with similar basin areas (14–20 km2). These basins had a range of disturbance caused by timber harvest, fire, and salvage logging. Mean channel gradient in sandstone was 0.012 m/m, and pools were the dominant habitat type. Mean channel gradient in basalt (0.025 m/m) was twice that in sandstone, and riffles were the dominant habitat type. Mean percentages by length of pools, glides, and riffles were 47, 33, and 20%, respectively, in sandstone, compared with 24, 27, and 50% in basalt. Channel gradient and channel morphology appeared to account for the observed differences in salmonid abundance, which reflected the known preference of juvenile coho salmon Oncorhynchus kisutch for pools. Coho salmon predominated in sandstone streams, whereas stee...

Populations of coastal cutthroat trout Oncorhynchus clarki clarki were sampled in 16 Oregon headwater streams during 1991–1993. These streams were above upstream migration barriers and distributed among basins that had been logged 20–30 and 40–60 years ago and basins that had not been logged but had burned 125–150 years ago. The objective of our study was to characterize the populations and habitats of age-1 or older cutthroat trout within these three forest management types. Streams within unlogged basins had relatively low levels and a small range of trout biomass (g/m2). Streams in basins logged 40–60 years ago supported low levels but an intermediate range of trout biomass. Streams in basins logged 20–30 years ago supported the widest range of biomass, including the lowest and highest biomasses among all streams sampled. The variable that best explained the variation of trout biomass among all 16 streams was the amount of large woody debris (LWD). All streams were heavily shaded during at lea...

The objectives of this study were to examine the interactions of the riparian setting (logged vs. forested) and prey availability on the prey capture efficiency and growth of cutthroat trout, and to determine if the riparian setting influences the impact of trout predation on drift composition. Short-term relative growth rates of cutthroat trout, experimentally confined in stream pools, were greater in a logged than in a forested section of stream. Differences in growth rates were attributed to differences among pools in invertebrate drift density, and to differences in trout foraging efficiency that were related to differences between the sections in the amount of overhead shading and substrate crevices. Mean percentages of introduced prey captured by trout were greater in logged control pools and pools of both sections whose bottoms were covered with fiberglass screening to eliminate substrate crevices than in forested control pools and logged pools that were artificially shaded. A logarithmic relationship was found between trout foraging efficiency and surface light of pools. Drift density significantly increased relative to controls in pools from which trout were removed in the logged reach, but not in the forested section. This may result from .habitat features in the logged section that favor greater trout foraging success and the occurrence of behaviorally drifting prey taxa, which represent a predictable food supply for the trout.

The temperature and dissolved oxygen content of intragravel water were measured in three Oregon coastal streams between June 1968 and June 1969. In 1966, the watershed of one stream had been completely clearcut, and that of a second stream partially clearcut in staggered settings. A third watershed was left unlogged. Clearcut logging resulted in increased temperature of intragravel water in salmon and trout spawning beds and decreased concentrations of dissolved oxygen. The changes were related largely to reduced forest cover over the stream surface and to deposition of fine sediment in the gravel. No serious reduction in survival to emergence of coho salmon occurred along with the observed changes in temperature or dissolved oxygen. A decrease in the resident population of cutthroat trout after logging may have been related to these changes.

This paper describes a method of direct measurement of the primary production of the benthic algal community in the lotic environment hat eliminates calculations of diffusion and is adaptable to the various chemical analyses used to indicate rates of production. 'This technique was developedl at Oregon State University, Corvallis, and supported by Research Grant WP 423, Federal Water Quality Administration. Benthic algal communities have been shown to be highly productive and may be more so than phytoplankton in shallow embayments (Odum et al. 1959; Pomeroy 1959; Smalley 1959; Teal 1959). In the lotic environment the significance of the benthic primary community varies. In headwater streams, allochthonous material may be more significant as a primary food source than the benthic algae produced in the stream (Chapman and Demory This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 14:57:21 PM All use subject to JSTOR Terms and Conditions