8147

• UCREFRP Catalog Number: 8147
• Author: Scoppettone, G. G.
• Title: Interactions Between Native and Nonnative Fishes of the Upper Muddy River, Nevada.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: YES

NATIVE AND NONNATIVE STREAM FISH INTERACTIONS

601

south Fork

I~

Sampled for relative
abundence

Upper

N
~20
km

Las
Vegas
o

115

N
.
I

o
I

0.5

1

km

Warm
Springs
Area

Moapa National
Wildlife Refuge

FIGURE 1. - Warm Springs, Nevada, area showing stream reaches sampled for relative abundances of adult Moapa
dace, Moapa White River springfish, shortfin mollies, and western mosquitofish. Inset shows the relationship of
the Muddy River and Warm Springs area to the Colorado River.

mate (Ricker 1975) was used to calculate popu-
lation size from recaptures:

N = (M + 1)(C + 1).
R + 1 '

N is population number, M is the number of fish
marked, C is the number of fish captured for cen-
sus, and R is the number of fish recaptured.
Population estimates were made for each reach,
and data were expanded to represent the entire
nursery stream. At least 15% of each reach of each
nursery stream was sampled.
Moapa dace did not trap reliably, so mark and
recapture was unsuccessful. In December 1984, I
counted adult Moapa dace with the aid of mask

and snorkel. Adult fish (2:40 mm TL) were count-
ed by snorkeling in an upstream direction. They
were generally in open water and not so sensitive
to my presence that they were difficult to count.
As I moved upstream, displaced fish swam around
and downstream from me, and were not counted
twice.
Spatial overlap in microhabitat. -Spatial mi-
crohabitat use by Moapa dace and Moapa White
River springfish larvae, juveniles, and adults was
determined by quantifying position of the fish in
the water column in terms of depth and water
velocity. The same quantification was made for
juvenile and adult shortfin mollies and western
mosquitofish; larvae of these species were as-