PARENT SESSION
PM15 - Field Studies: Causal Relationships Between Exposure & Effect
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P362) Spatial Patterns in the Movement and Distribution of Salmonids - the importance of water quality refugia.
Guillen, George*,1, Magneson, Mark1, 1 U.S. Fish and Wildlife Service, Arcata, Califorinia, USA
ABSTRACT- During the summer of 2001 we conducted a study to evaluate the response of adult and juvenile fish populations to degraded water quality in the Klamath River, California. Our hypothesis was that emigrating juvenile salmonid fishes maximize exposure to suitable microhabitat within the river system through behavioral modification and selective utilization of water quality "refugia" surrounding the mouths of tributaries. Our assessment of the role of temperature is presented as an example. During the survey period elevated temperatures (>21C) were detected in the mainstem Klamath River. Populations of juvenile salmonids responded positively to cooler tributary temperatures by congregating in large schools at the mouths of these waterbodies. As temperature levels in selected tributaries converged with mainstem temperatures during late summer and/or lower flows the fish would disperse and/or emigrate. Movement of fish may have been accelerated in areas were temperature convergence and/or elevated tributary temperatures existed. Results of this study illustrate the problems with assumptions surrounding traditional exposure scenarios used to evaluate contaminant risk. Traditional exposure assessments fail to represent the complexity of exposure regimes in rivers and their effect on organism survival and population dynamics. These "islands" of suitable water quality are extremely important and provide suitable refugia for fish thereby increasing survival rates. At the same time, organisms are crowded and therefore more subject to other density dependent factors (e.g. disease). Ecological risk assessments must take into account small scale patterns in contaminants and water quality to properly characterize risk and survival probability.
Key words: salmon, temperature, fish, Klamath