7872

• UCREFRP Catalog Number: 7872
• Author: Bestgen, K. R., et al.
• Title: Recruitment Models For Colorado Squawfish
• USFW Year: 1997.
• USFW - Doc Type: Tools For Evaluating Relative Importance Of Natural And Managed Processes - Final Report.
• Copyright Material: NO

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a function of the independent variables: predator TL, prey TL, (predator TL)2, (prey TL)2,
predator feeding strategy, water clarity, alternative prey, and second-order interactions.
red shiners exhibited different levels of predation that were not related to their size. We assumed
Predator feeding strategy was included as a predictor variable because each of the f ve groups of
these different behaviors represented the range of feeding strategies that were employed by
' groups of red shiners in the natural environment. A global model was fit using the method of
maximum likelihood, and model selection was by AIC. Model selection suggested that the best
' predictors of attack rate were prey TL, predator feeding strategy, water clarity, and alternative
' prey. Attack rate increased with larval size and was independent of red shiner size. Larger
' larvae- may be attacked more often than small ones because they aze more active and visible to
predators and because they aze energetically more profitable (Litvak and Leggett 1992, Bertram
' 1996). Cleaz water and the absence of alternative prey each increased attack rate 2-3-fold
' relative to conditions with turbid water or alternative prey present. The attack-rate equation had
the form:
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y = - 4.75 + 0.147•x, + 0.909•x2 + 1.157•x3 - 0.439 fs~ + 0.1036 fs2 - 4.45 fsj - 1.88 fs4
(4)

where: y =loge ((number of attacks• m2)• (larva• red shiner• 6 hour)'')
x, =prey TL,
x2 = 1 if water is clear; 0 if water is turbid,
x3 = 1 if alternative prey is absent; 0 if present,
fs, = 1 if simulating the feeding strategy of predator group 1; else = 0,
fs2 = 1 if simulating the feeding strategy of predator group 2; else = 0,
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