State of Washington
DEPARTMENT OF FISH AND WILDLIFE
Ecological Interactions Team, 201 N. Pearl St. Ellensburg, WA 98926

Summary of Upper Yakima River Rainbow Trout Status
Estimates For Sep/Oct 2003

Abundance of Fish Over 4" in Length
Average number of Rainbow Trout per river mile: 677 fish.
Most abundant is the Lower Canyon section with 1129 / river mile.
Least abundant is the Thorp section with 244 / river mile.
Total estimate of Rainbow Trout abundance from Roza Dam to the Cle Elum River confluence: 39,218 fish.

Size
The average length of Rainbow Trout (fork length): 9.8".
The average length of Rainbow Trout over 10" (fork length): 11.5".
The Cle Elum section had the largest average sized fish (of fish > 10" FL).
The Thorp section had the smallest average sized fish (of fish > 10"FL).
The average sizes of rainbow trout decreases as you move upstream with the exception of Cle Elum. However, the average size of fish over 10" decreased, with the exception of Cle Elum. The largest Rainbow Trout observed this year was in the Cle Elum section and was 21.4" long (total length)

Distribution
The Lower Canyon and Ellensburg reaches contained the largest number of fish per mile in 2003.

The following equation was developed to calculate the weight of a mainstem Yakima River Rainbow Trout from a measured fork length (in inches). This equation is based on the lengths and weights taken from over 21,500 fish. With this technique, you can calculate the weight of a fish you caught while minimizing the amount of handling on that fish.

Weight in lbs. = 0.0005 x (measured fork length in inches) ^ 2.9298
WDFW Ecological Interactions Team

Many hand held calculators have a button labeled y^x . To use this function, you enter the fork length you measured into the calculator, then press the y^x button once, and enter 2.9298, then press the = button. Next press the multiplication, or X button once, and enter 0.0005 and then press the = button. The result is the weight of the fish in pounds. For example, the weight of a 14.5" Rainbow Trout would be:

Weight in lbs = 0.0005 x (14.5) ^ 2.9298 = 1.2634 or about 1.3 lbs


For more data see: Yakima River rainbow trout population. Also, detailed information including WDFW annual reports is available in PDF format at www.ykfp.org.