Short communication: A climate-based index of historic spawning-stream hydrology

Kaeding, L.

gear Creek temperature revealed which is a key spawningoral trends in tservations have implications forReproductive success of stream-spawning Oncorhynchus fishes (Pacific salmon, rainbow trout, cutthroat trout and their allies) may be greatly affected by stream discharge or its covariate, stream temperature, during the spawning season. Because such data for the physical environment may not have been routinely collected as part of previous investigations of these fishes, identification of simple but robust indices of historic, seasonal stream discharge and temperature, using long-term climate data sets, would be important, especially to investigations of historic population dynamics. This study examined statistical associations among several climate variables and the spawning-season (approximately June) discharges and temperatures of Clear Creek, a Yellowstone Lake tributary used by spawning Yellowstone cutthroat trout, Oncorhynchus clarkii bouvieri (YCT), from the lake. Correlation analysis showed that total water-year degree-days (calculated on the basis of mean daily air temperature>0C) at Lake Village, on the lake’s north shore, was a robust index (both negative and positive, respectively) of consecutive, total semi-month metrics of creek discharge and temperature during the YCT spawning season. This study (and subsequent use of the Lake Village deree days metric as an environmental variable in a dynamic, age-structured model of the lacustrine–adfluvial YCT population of Cl) showed how exploratory analyses of the fragmentary but long-term and regionally unique data sets for Clear Creek discharge anda simple but robust index of climate variation important to understanding the historic dynamics of Clear Creek’s YCT population, stock of Yellowstone Lake. In addition, the extensive statistical associations among the climate variables, along with the tempwo key variables, broadly showed how climate varied across the Yellowstone Lake region during the past several decades. Those ob the historic, seasonal hydrology of all Yellowstone Lake tributaries used by spawning YCT.