9697

• UCREFRP Catalog Number: 9697
• Author: Bestgen, K.R., D.W. Beyers, J.A. Rice and G.B. Haines.
• Title: Factors affecting recruitment of young Colorado pikeminnow
• USFW Year: 2006.
• USFW - Doc Type: synthesis of predation experiments, field studies, and individual-based modeling.
• Copyright Material: YES

YOUNG COLORADO PIKEMINNOW RECRUITMENT

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FIGURE 2.- The Green River basin study area Primary spawning areas are in Yampa Canyon and Gray Canyon downstream of
river kilometer (RK) 251. Primary nursery habitat for age-O pikeminnow was the middle (RKs 34~515) and lower (RKs ~211,
where RK 0 is at the Colorado River confluence) Green River. Circles indicate cities.

(Figure 2). Spawning begins 4--6 weeks after peak
spring runoff, when water temperatures exceed 16-
180C, and extends up to 6 weeks (Nesler et al. 1988;
Tyus and Haines 1991; Bestgen et al. 1998). Embryos
deposited over cobble bars develop in interstitial spaces
for 4--6 d at temperatures of 18-260C (Han1IDan 1981;
Bestgen and Williaoas 1994). Emerging larvae, 7-9
mm TL, are transported by river currents 40-200 Ian or
more downstream to low-gradient valley reaches,
where they occupy shallow, low-velocity backwater
nursery habitats (Bestgen and Willianas 1994; Bestgen
et al. 1998) for the duration of the growing season
(Tyus and Haines 1991). Growth, survival, and
recruitment of early life stages of Colorado pike-
minnow in their first summer of life is the primary
focus of this paper.

Methods
Laboratory Experiments

Experiments were conducted in aquaria and in
mesocosms that simulated nursery habitat conditions,

so that size-dependent predator-prey interactions and
effects of turbidity, alternative prey, and predator
behavior could be described. The likelihood of a fish
larva being eaten by a predator is the product of at least
three probabilities: the probability of being encountered
by a predator, the probability of being attacked if
encountered, and the probability of being captured if
attacked (Gerritsen and Strickler 1977). We conducted
experiments to determine red shiner probability of
capture and encounter rates, so that the mM could be
constructed using data specific to the system and fishes
of interest. We present findings of some experimental
data in Methods to facilitate understanding and
st:J:earnline presentation of laboratory and modeling
results later.
Probability of capture.-Data !hat described the
probability that a Colorado pikeminnow larva would be
captured by a red shiner when an attack occurred were
collected by observing the outcome of predation events
in laboratory aquaria. A 6 X 6 factorial design was
used. The first factor, predator size (mean TL), had six