Spatial Structure in the Spawning and Distribution Patterns of Snake River Finespotted Cutthroat Trout in the Upper Snake River

Potamodromous cutthroat trout express multiple life-history strategies that appear to be directly related to the physical habitat in which they evolved.  Although there is a substantial amount of information concerning the habitat use and distribution patterns of cutthroat trout that live in lakes and ascend tributaries to spawn, information about populations in lotic environments is less abundant.  Most of these studies have focused on the migration and spawning dynamics of cutthroat trout moving into tributaries to spawn.  In larger river systems, however, spatiotemporal relationships between physical characteristics of the habitat and life-history organization of cutthroat trout may be more complicated.  To better understand the life-history organization, distribution patterns, and habitat use of Snake River finespotted cutthroat trout Oncorhynchus clarkii behnkei in the upper Snake River, we implanted radio transmitters in 248 cutthroat trout and monitored movement patterns for 12 months.  A total of 122 cutthroat trout spawned in 2009 in 22 spawning areas.  The majority of spawning occurred in spring creeks or side channels of the Snake River, although two tributaries were also major spawning areas.  Distribution patterns of these spawners were spatially structured during the year spawning occurred.  As a consequence of this spatial structure, habitat use varied among individuals from different spawning areas.  In an effort to explain patterns of habitat selection, we are currently examining spatial relationships among available habitat, areas used for spawning, and the timing of life-history events.  Results will provide riverscape-scale insights into factors influencing distribution and habitat selection of potamodromous trout in a large river network.