A CLIMATE-BASED INDEX OF HISTORIC SPAWNING-STREAM HYDROLOGY

Reproductive 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>0 degrees C) 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 degree days metric as an environmental variable in a dynamic, age-structured model of the lacustrineadfluvial YCT population of Clear Creek) showed how exploratory analyses of the fragmentary but long-term and regionally unique data sets for Clear Creek discharge and temperature revealed a simple but robust index of climate variation important to understanding the historic dynamics of Clear Creek's YCT population, which is a key spawning stock of Yellowstone Lake. In addition, the extensive statistical associations among the climate variables, along with the temporal trends in two key variables, broadly showed how climate varied across the Yellowstone Lake region during the past several decades. Those observations have implications for the historic, seasonal hydrology of all Yellowstone Lake tributaries used by spawning YCT. Copyright (c) 2011 John Wiley & Sons, Ltd.