Thermal limitations on chinook salmon spawning habitat in the northern extent of their range

Abstract

Pacific salmon (Oncorhynchus) habitat models attempt to balance research efficiency with management effectiveness, however, model transferability between regions remains elusive. To develop efficient habitat models, we must understand the critical elements that limit habitat. At the northern edge of the geographic range for Chinook salmon, O. tschawytscha, water temperature is a probably a limiting habitat factor. This study investigated the spatial and temporal correspondence between water temperature and Chinook salmon spawning on the Chena River, Alaska. Water temperatures were monitored at 21 stations across 220 river kilometers during the 2006 and 2007 spawning seasons and compared to known thermal requirements for egg development. While an absolute upstream thermal boundary to spawning was not discovered, we describe potential temporal limitations in thermal conditions over the spawning season. Our results show that 98.5% of Chinook salmon selected spawning habitat in which their eggs have a 90% probability of accumulating 450 ATUs before freeze up. This suggests not only temperature conditions limit salmon spawning habitat, but also, as expected, water temperatures temporally limit accessible Chinook salmon spawning habitat at the northern edge of their range. This project documents new spawning habitat for the Anadromous Waters Catalog and broadens the geographical range of Chinook salmon thermal habitat research. It also contributes to the understanding of the processes that define salmon habitat, while providing a baseline for further investigations into water temperature in other thermal regimes.