Factors affecting growth of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri) in alpine lakes, of the Absaroka-Beartooth Wilderness, Montana

The purpose of this study was to determine factors responsible for poor growth of Yellowstone Cutthroat Trout in Kookoo Lake, an alpine lake in the Absaroka-Beartooth (A-B) Wilderness, and to examine factors related to the variation in growth rates of cutthroat trout in other A-B Wilderness lakes.The influence of these factors on growth rates should be considered when stocking alpine lakes.Major objectives of this study were to use historical data from 1956-1997 for 71 A-B lakes stocked with Yellowstone Cutthroat Trout to (1) establish mean age-length relationships, (2) correlate growth rates to stocking sequence, stocking density, and physical characteristics of alpine lakes, and to use field methods to (3) compare physiochemical and biological characteristics of two similar A-B lakes that exhibit contrasting growth rates.Based on stocking and gill net records obtained from the Montana Fish, Wildlife and Parks mean lengths were established for ages 1-10 for cutthroat trout.Stocking density, stocking sequence, lake elevation, depth, area, and volume were correlated with growth rates using stepwise multiple regression, and were examined for trends.Kookoo Lake and Triangle Lake were examined to establish profiles for temperature, dissolved oxygen, pH, nitrate, ammonia, phosphate, and chlorophyll-a concentration.Biological activity was compared using diel fluctuations of dissolved oxygen and pH.Heavy metal concentrations were noted at the surface and bottom.Light penetration was determined from Secchi measurements.Discharge was measured, and flushing rates calculated.Benthos and zooplankton were counted and identified.Fish were stocked in both lakes at 247/ha in 1994, but were absent from Triangle Lake in 1995.Growth and health of fish in Kookoo Lake was monitored through 1997.Stocking sequence (p=0.026),stocking density by area (p=0.003), lake elevation (p=0.007), and lake volume (p=0.025)correlated negatively with growth.Biological productivity was lower in Kookoo Lake compared to Triangle Lake as measured by dissolved oxygen flux(0.70 to 0.97 mg/L.h,respectively) and carbon dioxide flux(0.007 to 0.031 mg/L.h,respectively).Extremely high flushing rates of 2-9 d in Kookoo Lake caused a washout of nutrients and organisms lowering productivity when compared to Triangle Lake, although nitrogen levels were consistently higher in Kookoo Lake.The nitrogen:phosphorus atom ratios of Kookoo Lake (23:1-June 94, 20:1-July 94 and 9:1 August 94) indicated a mainly phosphorus limited system, while Triangle Lake was limited by nitrogen concentration's (3:1, 12:1 and 7:1).Zooplankton densities were five to ten times higher in Triangle Lake where the population was dominated by cladocerans, while the smaller Kookoo Lake population was dominated by copepods.The lower productivity of Kookoo Lake probably made the zooplankton population more susceptible to the high trout stocking density initially used, resulting in an altered zooplankton community, excluding most cladocerans, and reducing population density.Growth rates are highly variable in alpine lakes with stocking density, stocking sequence, lake elevation, lake depth, lake area, and lake volume accounting for only 9.8% of difference in growth.This study indicates that flushing rate also has an impact on productivity in alpine lakes.Further study of flushing rate and other factors that may influence growth is needed.Adjustments of trout stocking V