Thursday, August 9, 2007 - 8:20 AM

COS 106-2: Fall home-range size and movement patterns of Columbia River redband trout (Oncorhynchus mykiss gairdneri) in a sagebrush desert stream

Chris A. Walser, Lucas F. Stringfield, and Nick Piccono. Albertson College of Idaho

The Columbia River redband trout (Oncorhynchus mykiss gairdneri) is the only trout native to sagebrush desert basins of southwestern Idaho.  The redband trout occupies 64% of its historic range (inland drainages of the Pacific Northwest) and is listed as a species of special concern in Idaho, Oregon, and Montana. The objective of this study is to determine redband trout fall home-range size and movement patterns; and to examine if individual fish exhibit a high degree of year-to-year stream reach fidelity.  In September 2005, radio telemetry tags were surgically implanted into 15 adult (>150-g) trout.  Fish were collected from a 7-km reach of Jordan Creek, a 4th order tributary of the Owyhee River basin in southwestern Idaho.  Trout were tracked weekly for 55-d.  Fish locations were incorporated into an ArcGIS database for analyses. Mean home-range size of redband trout was 397-m (SD=365-m; range=13-1041-m).  Total distance moved by all fish during the study ranged from 29-m to 1197-m (mean= 460-m; SD=374-m).  Median weekly distance traveled by fish during late September (median=6-m) was not significantly different from distances traveled during late October (median=28-m) (p=0.24, UA=89). The majority of fish (79%) moved downstream and the movement appeared to be associated with the availability of complex pools for over-wintering. To examine long-term fidelity of trout for the 7-km study reach, we PIT tagged 202 adult fish over a 4-y period.  Annual summer and fall surveys resulted in a 2.5% recapture rate, indicating the likelihood of extensive year-to-year movement of redband trout in this system.  Redband trout in Jordan Creek occupy a much larger fall home-range size and exhibit more extensive movements than other redband trout populations. Our results lend strong support for the development of population-specific Columbia River redband trout conservation plans.

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