Christine L. May

The Relationships among In-Channel Sediment Storage, Pool Depth, and Summer Survival of Juvenile Salmonids in Oregon Coast Range Streams

Abstract The influence of channel aggradation on water availability and salmonid survival was investigated during the summer dry season in two Oregon Coast Range streams. Deep pools and a deformable streambed of coarse gravel were present in highly aggraded stream reaches. However, these thick, highly porous alluvial deposits caused surface flow to become intermittent, which stranded fish in drying channels. In gravel-bed reaches with thinner alluvial deposits, pool depth was limited by the underlying bedrock, but pools were sustained by hyporheic flow throughout the summer dry season. In these moderately aggraded reaches, pool depth and area decreased throughout the summer, resulting in severe crowding of fish trapped in pools formed over small patches of exposed bedrock and isolated by dry, gravel-bed riffles. Bedrock-dominated stream reaches had slightly smaller pools but were most likely to contain continuous surface flow throughout the summer dry season; these reaches exhibited the smallest decreases...

Quantitative linkages among sediment supply, streambed fine sediment, and benthic macroinvertebrates in northern California streams

Abstract The absence of quantified relationships among sediment supply, stream channel conditions, and biological responses limits our ability to predict the cumulative watershed effects of management activities in forested mountainous watersheds. We addressed this uncertainty by testing whether increased sediment supply resulted in elevated levels of streambed fine sediment stored in pools and riffles and whether fine bed material was correlated with spawning-gravel quality and altered benthic macroinvertebrate assemblages in 6 streams of the Klamath Mountains, northern California. Sediment supply was estimated using 2 models: 1) an empirical model of landslide volumes based on terrain types present in a basin, and 2) a surface erosion model using a locally calibrated version of the universal soil loss equation. Riffle-surface fine sediment and the fractional volume of pools filled with fine sediment (V*) were both positively correlated with estimated sediment supply, whereas subsurface spawning-gravel permeability was inversely correlated with estimated sediment supply. Fine sediment levels were relatively low compared to published values. Reach-average values of riffle-surface fine sediment ranged from 4 to 16% and V* values ranged from 0.05 to 0.20. Based on established relationships between subsurface flow rates and salmonid egg survival, median predicted egg survival was quite low and ranged from 15 to 38%. Riffle-surface fine sediment and common benthic macroinvertebrate biological metrics were not correlated, but several taxa showed responses to riffle-surface fine sediment. Taxa that showed negative responses to fine sediment are hypothesized to be more available as prey for salmonids than taxa that showed positive responses. This relationship suggests that fine sediments might cause an overall reduction in prey availability for salmonids. Monitoring the effects of increased sediment supply in steep, forested streams should focus on fine sediment in pools and riffles, salmonid spawning-gravel quality, and specific macroinvertebrate taxa that are especially responsive to fine sediment. The linkages described in our paper can be used to make quantitative predictions of the cumulative watershed effects of management activities on stream conditions, salmonid habitat, and benthic macroinvertebrates.

River profile controls on channel morphology, debris flow disturbance, and the spatial extent of salmonids in steep mountain streams

Received 29 December 2011; revised 5 September 2012; accepted 17 September 2012; published 27 October 2012. [1] In the geologically and topographically diverse mountain ranges of the Pacific Northwest, a broad-scale means of prioritizing salmonid habitat conservation areas based on geomorphic process domains is examined. We propose that steepness and concavity indices derived from the relation between drainage area and channel slope provide a means of identifying basins that express different reach-scale morphologies, fish habitat capacity, and risk of episodic disturbance. Strongly concave river profiles that develop in mountainous terrain indicate that almost all of the relief in the drainage network occurs in headwater streams. In these basins a large proportion of the channel network has low-gradient morphologies, which provide favorable habitat for many salmonid species. The severity of pulse disturbances is also reduced because low-gradient main stem channels inhibit debris flow conveyance, and in these networks the distribution of fish can expand into tributaries, allowing for a spatial spreading of risk. In contrast, rivers with poorly concave or steeper profiles have a greater abundance of high gradient reaches that limit the distribution of fish to a small portion of the channel network and facilitate debris flow-passage. The combined influence of a limited spatial distribution of fish and an increased risk of debris flows may cause populations in these basins to be less resilient to pulse disturbances. A case example from the Klamath Mountains, an area with broad variation in the steepness and concavity of river profiles, was used to develop this approach and aid conservation planning for imperiled populations of anadromous salmonids.

Social hierarchies override environmental conditions in determining body coloration of brook trout

ABSTRACT Dynamic changes in body color are commonly used as a means of intraspecific communication and for crypsis. It is well established that subordinate fish signal to dominant fish by darkening their body color. Similarly, salmonids can adapt their body color to match their environment. What is not known is whether social interactions or environment plays a larger role in driving dynamic changes in body color, as these factors rarely occur in isolation. Experiments conducted in artificial stream channels with wild brook trout tested for the potential of color matching by varying light and dark substrates and included treatments with individuals as well paired cohorts to test for the effect of social hierarchies. Fish displayed a broad ability to adapt their coloration to match a range of substrates, with a strong preference for dark substrate. In paired trials, dominant fish matched light substrate more effectively while subordinates displayed darker coloration, resulting in subordinates being poorly matched to their surroundings. Mismatching the environment in order to send appropriate social signals could have negative consequences that further reduce fitness in subordinate fish.