• River features associated with chinook salmon spawning habitat in Southwest Alaska

      Jallen, Deena M.; Margraf, F. Joseph; Adkison, Milo (2009-08)
      Chinook salmon (Oncorhynchus tshawytscha) is a highly valued traditional, subsistence, and commercial resource in Southwest Alaska. Stream habitat availability is a major component influencing salmon productivity. The objective of this study is to identify river features associated with spawning habitat, and describe upper and lower boundaries of chinook salmon spawning on the Tuluksak River. River distances, elevation, salmon locations, spawning sites, and habitat observations were collected along 75 river kilometers of the Tuluksak River primarily within the Yukon Delta National Wildlife Refuge. Habitat and salmon observations were grouped into strata along the length of the river for comparison and analysis. Chinook salmon were observed spawning in the upper 45 river kilometers of the study area. Map-based observations of elevation and channel sinuosity correlate better with chinook salmon spawning than in stream habitat measurements along the Tuluksak River. The upper boundary of chinook salmon spawning in the Tuluksak River was outside of our study area. The lower boundary for chinook salmon spawning habitat on similar rivers might be determined by examining elevation, sinuosity, and channel features from remote images or maps prior to conducting field studies.
    • Thermal limitations on chinook salmon spawning habitat in the northern extent of their range

      Decker, Samantha Kristin Strom; Margraf, F. Joseph; Rosenberger, Amanda; Evenson, Matthew (2010-05)
      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.