Homing Vs. Straying: Spawning Patterns of Fluvial Yellowstone Cutthroat Trout in the South Fork Snake River

The South Fork of the Snake River (SFSR) is home to a robust population of fluvial Yellowstone Cutthroat Trout, (YCT) Oncorhynchus clarkia bouvieri.  Four main tributaries of the SFSR (Burns, Pine, Rainey, and Palisades Creeks) have been recognized as critical spawning areas for fluvial YCT by the Idaho Department of Fish and Game.  Weirs have been installed on these tributaries in order to protect the genetic integrity of fluvial YCT from introgression with Rainbow Trout Oncorhynchus mykiss.  The objective of this study was to determine the patterns of homing and straying of fluvial YCT within the main tributaries of the SFSR system. Homing was defined as an adult that returned to the same tributary over multiple years during the spawning season, whereas straying adults entered multiple tributaries over multiple years.  Of the 852 recaptured fluvial YCT, >98% demonstrated patterns of homing.  Since 2001, significantly fewer fluvial YCT have returned to spawn in Rainey Creek compared to the other tributaries.  The strong patterns of homing found in the study suggest that bolstering the YCT stock in Rainey Creek could potentially enhance fluvial YCT spawning in this tributary, provided that habitat (e.g. spawning or juvenile rearing habitat) is not a limiting factor.