8140

• UCREFRP Catalog Number: 8140
• Author: May, B. E., J. D. Leppink and R. S. Wydoski.
• Title: Distribution, Systematics and Biology of the Bonneville Cutthoat Trout,
• USFW Year: 1978.
• Copyright Material: NO

years in New Mexico (Jester and McKirdy 1966). It is believed that stream
habitat improvements can benefit trout populations in small streams in the
Intermountain West (Wydoski and Duff 1978).
Reproduction
The sex of all fish used for growth evaluation was determined by macroscopic
examination of the gonads. Males were judged to be mature if they had enlarged
testes or testes with residual sperm pockets. Females were judged to be mature
if they contained residual eggs from a previous spawning or had eggs that were
developing. The majority of cutthroat trout (57.3 percent of 68) in these two
collections were males; however, larger fish were selected during sampling in
September 1973 for electrophoretic analysis. Therefore, the June 1975 sample
was perhaps more representative of the sex ratio in which 43.6 percent of 39
trout were males.
Further reproductive analysis of the Birch Creek population was conducted
during the spring of 1977 in conjunction with an on-going management pro-
grams During that sampling, males comprised 50 percent of the fish observed.
Sex ratios for cutthroat from Trout and Birch creeks, Juab County, were similar
to Birch Creek, Beaver County (Hickman 1977).
No male cutthroat trout of Age Group I from Birch Creek were mature;
however, seven of eight males from Age Group II were mature. All males longer
than 134 mm (5.25 inches) in total length were mature. No females were mature
in Age Groups I and II. Females were first mature in Age Group III (1 year later
than males); the smallest mature female fish was 147 mm (5.7 inches) in total
length.
Three females in the September 1973 collection contained developing eggs
and were completing their third summer of life. These trout contained: Ninety-
nine eggs (2 mm diameter) in a fish 147 mm (5.7 inches) total length and
weighing 39 g (0.081bs.); 60 eggs (1.5 mm in diameter) in a fish 158 mm (6.25
inches) total length and weighing 45 g (0.09 lbs.); and 176 eggs (1.5 mm in
diameter) in a fish 176 mm (7.0 inches) total length and weighing 75 g (0.171bs.).
Spawning in Birch Creek began during early May and continued until June.
Water temperature was 6.7°C (44°F) during peak spawning activity. Spawning
was first noted in the lower reaches of the stream and then progressed upstream.
Water temperatures in the upper and lower stream reaches varied up to 2°C
(5°F). Hickman (1977) observed ripe cutthroat trout during late May and re-
ported that spawning was completed in Trout Creek mid- to late June.
MANAGEMENT IMPLICATIONS
When managing fish populations, biologists, administrators, and the public
must be prepared to accept variation, dynamic populations, a largely un-
controllable environment, the need for compromises, the need to deal in op-
timum rather than maximum results, and conflicting desires of the angling
public (Everhart et al. 1975). These variables would be the same in managing a
fishery for large rainbow trout or managing small and little known endemic
cutthroat fishery.
Past management efforts directed specifically toward Bonneville cutthroat
have been largely non-existent. When white settlers first entered the Bon-
neville Basin, S. c Utah abounded in all streams and lakes. Cutthroat trout
6Utah cutthroat trout management proposal for the Southern Region prepared January 1977;
approved February 1977 as an integral part of Southern Region fishery management.
19