Using otoliths and scales to describe age and growth of Yellowstone cutthroat trout in a high-elevation stream system, Wyoming

Estimates of age and lengths at specific ages of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri Richardson) were made using otoliths and scales. Fish were sampled from 17 high-elevation streams in the Greybull River drainage, Wyoming. Variation in estimates of age within and among three readers were assessed using both structures. Variability among age estimates by individual readers was low for both structures. Estimates using otoliths were significantly less variable than were estimates based on scales both among readers and among estimates by individual readers. Otoliths were more accurate than scales for estimating the correct age of fish. Back-calculated estimates of fish lengths at given ages based on otoliths were significantly less than those based on scales, Hatchery fish grew faster than wild fish at younger ages. Overall, growth of wild fish was slower than in other areas where Yellowstone cutthroat trout are endemic. We predict that if otoliths were used instead of scales to assess age and growth of other trout species in high-elevation streams that similar differences in estimates based on the two structures would be observed.