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<br />Transactions of the American Fisheries socrety 135:1722-1742, 2006
<br />@ Copyright by Ibe American Fisheries Society 2006
<br />001: 1O.1577{f05-171.1
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<br />[Article]
<br />
<br />Factors Affecting Recruitment of Young Colorado Pikeminnow:
<br />
<br />Synthesis of Predation Experiments, Field Studies, and
<br />
<br />Individual-Based Modeling
<br />
<br />K. R. BESTGEN* AND D. W. BEYERSI
<br />Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Coloradn Slate University,
<br />Fort Collins, Colorado 80523-1474, USA
<br />
<br />J. A. RICE
<br />
<br />Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695-7617, USA
<br />
<br />G. B. IlAINEs
<br />
<br />U.S. Fish and Wildlife Service, Colorado River Fishery Project,
<br />1380 South 2350 West, Vernal, Utah 84078, USA
<br />
<br />Abstract.-Predation experiments, field studies, and individual-based-model (IBM) simulations revealed
<br />factors that affected the swvival and recruitment of early life stages of endangered Colorado pikeminnow
<br />Ptychocheilus lucius in the Green River basin, Utah and Colorado. Small-bodied, nonnative red shiners
<br />Cyprinella lutrensis attacked Colorado pikeminnow larvae an average of once per minute, and predation
<br />success approached 30% in laboratory aquaria. Attack rate was also high in mesocosm experiments; turbidity
<br />and alternative prey reduced predation success. Distributions of hatching dates derived from otolith daily
<br />increment analysis showed that large cohorts of Colorado pikeminnow larvae that hatched in the Green River
<br />in early summer had low survival to autumn and that the few survivors were fast growing. Larvae hatched in
<br />midsummer or later had higher survival. Autumn juveniles grew 12-73% faster than summer juveniles, which
<br />suggested differential mortality of slow-growing fish. The ffiM simulations integrated size-dependent
<br />predator--iJTeY relationships, Colorado pikeminnow life history information, temperature-dependent pike-
<br />minnow growth, Green River predator size-structure dynamics, seasonally variable Green River water
<br />temperatures, and turbidity and alternative prey availability effects; the simulations showed that red shiner
<br />predation interacting with environmental variables may significantly reduce age-O pikeminnow recruitment in
<br />autumn. Recruitment and growth patterns from simulations and field observations were consistent and
<br />suggested that the ffiM is useful in evaluating management scenarios. Experiments, field studies, and
<br />predictive modeling provided consistent evidence that interacting effects of predation and environmental
<br />variables, including flow fluctuations, may structure intra-annual growth and recruitment patterns of age-O
<br />Colorado pikeminnow. Flow management to benefit growth and survival of young pikeminnow, particularly
<br />early hatching ones, and reduced nonnative predator abundance in Green River backwaters may enhance the
<br />Colorado pikeminnow populations.
<br />
<br />Recruitment is central to the population ecology of
<br />fish because the abundance and survival rates of young
<br />in a cohort can have a strong influence on year-class
<br />strength in later life (Hjort 1914; Thorson 1950;
<br />Roughgarden et aI. 1988). Factors that affect recruit-
<br />ment variation are of theoretical and practical interest
<br />(Hilborn and Walters 1992) and are often a focus of
<br />managers charged with resource conservation and
<br />recovery. Understanding the mechanisms that regulate
<br />recruitment is challenging because life history process-
<br />
<br />* Corresponding author. kbestgen@cnr.colostate.edu
<br />I Present address: 330 Smythe Drive, Williams Bay,
<br />Wisconsin 53191, USA.
<br />
<br />Received Iune 27, 200S; accepted March 28, 2006
<br />Published online November 30, 2006
<br />
<br />es such as the timing and success of reproduction,
<br />growth, and rates of survival and dispersal of young are
<br />influenced by biological and physical factors (Thorson
<br />1950; Connell 196I; Roughgarden et aI. 1985; Fogarty
<br />et aI. 1991; Magnuson 1991). For example, fluctuations
<br />in physical characteristics of rivers (e.g., discharge,
<br />water temperature, and sediment transport regimes) can
<br />influence timing of reproduction and habitat availabil-
<br />ity, which in turn affect growth and survival of early
<br />life stages offish (Welcomme 1979; Crecco and Savoy
<br />1985; Limburg 1996; Mion et aI. 1998). Biological
<br />processes such as predation, competition, and starva-
<br />tion can interact with physical factors and affect
<br />recruitment of young (May 1974; Hunter 1981; Houde
<br />1987; Bailey and Houde 1989). Because the impor-
<br />tance of physical and biological processes may shift
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