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

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Growth rate (mm TUd)

FIGURE 1O.-Frequency distributions (means of five
simulations) of growth rates of Colorado pikeminnow larvae
in the Green River, Utah, with and without size-dependent
predation by red shiners, as derived by an individual-based
recmitment model. Individuals in both cohorts were assigned
a growth rate by random draw from an initial distribution of
growth rates that had a mean of 0.4 rnrn/d (SD = 0.07).

in both simulations and the field, except for the middle
Green River field data in 1991.
The mean TLs of Colorado pikeminnow from field
data and ffiM simulations were generally similar across
river reaches and years (Table 1; Figure II). The
largest discrepancy was for the middle Green River,
1991, where mean length of Colorado pikeminnow
juveniles in autumn was 4.9 mm greater than predicted
from simulations. The ffiM simulations did not predict
the mode of late-hatching and relatively small
Colorado pikeminnow observed in field samples, but
simulated and field-collected fish had identical mean
11... Generally, length distributions were broader for
wild fish than for simulations, probably a result of
conservative estimates of the SD of growth rates used
in simulations.

Discussion
We used experiments, field observations, and
simulation modeling to produce a relatively compre-
hensive assessment of factors affecting recruitment of
early life stages of {;:olorado pikeminnow. Small-scale
laboratory experiments provided the basis for under-
standing a precise mechanism, size-dependent preda-
tion by red shiners on early life stages of Colorado
pikemirmow and allowed estimation of effects of
relevant field variables, such as turbidity and alterna-
tive prey, on predation. Field studies in the Green River
provided scale-appropriate observations of the entire
recruitment process for early life stages of Colorado
pikemirmow, including observations of timing and
intensity of spawning, effects of stochastic flow events,
and patterns of intra-armual variation in recruitment
and growth that were correlated with important but
uncontrolled envirornmental variables. Congruence of
recruitment hypotheses generated from laboratory

BESTGEN ET AL.

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Colorado pikeminnow TL (mm)

FiGURE 1 L-Size-distributions of age-O Colorado pike-
minnow captured in autumn in the middle (MGR) and lower
Green River (LGR), Utah, in 1991 and 1992 (black ban;)
compared with individual-based recruitment model simula-
tions (white ban;) that used drift-net captures of larvae as
cohort inputs.

experiments and field data were evaluated with a
model. The data-driven ffiM we developed integrated
numerous interacting factors, including seasonally
varying water temperature and predator-size dynamics,
and allowed evaluation of importance of those specific
mechanisms to the recruitment process that would not
be obvious from results of laboratory experiments or
field observations alone. The ffiM simulations pro-
duced predictions that were generally consistent with
field observations, even though we only considered