8097

• UCREFRP Catalog Number: 8097
• Author: American Fisheries Society.
• Title: Proceedings of the 18th Annual Meeting, Colorado - Wyoming Chapter, American Fisheries Society.
• USFW Year: 1983.
• USFW - Doc Type: March 2-3, 1983.
• Copyright Material: NO

THE BROWN TROUT FISHERY IN DILLON RESERVOIR,
COLORADO, 1979-1980

JAMES A. DAVIS
GRADUATE RESEARCH ASSISTANT

CLARENCE A. CARLSON
PROFESSOR IN FISHERY BIOLOGY

DEPARTMENT OF FISHERY AND WILDLIFE BIOLOGY
COLORADO STATE UNIVERSITY
FORT COLLINS, COLORADO 80523

ABSTRACT

Mean length and weights for brown trout (Salmo trutta)
collected from Dillon Reservoir and the Blue River were signifi-
cantly lower in 1980 than in 1979. Growth of brown trout 2-4
years of age was slowest and growth of brown trout 5-6 years of
age was fastest. The length-weight relationship was almost
identical in 1979 and 1980. Condition tended to decrease in
brown trout 2-4 years of age and increase in older fish. Female
brown trout outnumbered males during the 1979 and 1980 spawn-
ing migrations up the Blue River. Total number of brown trout
in the Blue River spawning migration has declined since 1977.
Total number of brown trout harvested from Dillon Reservoir
was estimated to be 2063 and 1407 in 1979 and 1980, respectively.
Catch per angler hour was 0.011 and 0.009 in 1979 and 1980,
respectively. Angler hours per season were 183,251 and 149,940
in 1979 and 1980, respectively. Brown trout spawning habitat
was 1.8% (936 m2) of the total Blue River study area (50,841 m2.
Much of the available spawning habitat was confined to small
areas along streambanks. Spawning substrate ranged 0.25-76 rom
in diameter with 16-64 rom the most abundant category.

INTRODUCTION

Historically, Dillon Reservoir has provided anglers with an opportunity
to catch trophy-sized brown trout (Salmo trutta). In recent years, local
anglers have voiced concern over the dwindling number of large brown trout
being harvested. In response, the Colorado Division of Wildlife initiated a
2-year study to determine the "status" of the brown trout population in
Dillon Reservoir. Three objectives were established: 1) to determine the
age, growth, sex ratio and total number of borwn trout in the spawning popu-
lation; 2) to determine the effect of harvest on mature brown trout; and 3)
to determine the amount of spawning habitat in the Blue River, a tributary
to Dillon Reservoir. This paper provides a report on that study.

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