9592

• UCREFRP Catalog Number: 9592
• Author: Mueller, G. A., J. Carpenter and P. C. Marsh.
• Title: Cibola High Levee Pond Annual Report 2004.
• USFW Year: 2004.
• USFW - Doc Type: \
• Copyright Material: NO

and to consider the impact of other small-bodied non-natives on razorback larvae as well. We
have focused on non-natives that are common in the lower Colorado River.

This was the second year of predator/prey tank tests. In 2003, we tested red shiner, young of the
year (yay) and adult rainbow trout (Oncorhynchus mykiss), and yay bluegill (Lepomis
macrochirus) and bonytail (as a native "control" species) on razorback larvae <15 mm. We also
tested young channel catfish (Ictalurus punctatus), largemouth bass (Micropterus salrnoides),
and yellow bullhead (Ameiurus natalis) on larvae that were 15-30 mm. In 2004, we tested
predation on razorback eggs as well as on larvae <15 mm. Razorback sucker eggs and larvae
were supplied by USFWS while non-natives were captured nearby or purchased from
aquaculturists. All tests in 2004 were conducted at the Achii Hanyo Fish Facility. Details of the
experimental design can be found in our 2003 Annual Report (Mueller et al. 2003).

At least two control tanks (eggs or larvae with no predator) were used in each predator trial.
Trials ended when we removed predators and counted either the number of visible eggs or
surviving larvae. Weights, lengths, and gape measurements of predators were recorded at the
completion of experiments.

Egg Predation Experiments-We tested the ability of tadpoles and crayfish to prey upon
razorback sucker eggs. Our methodology was simple: we placed 20 eggs in 10-gal tanks with no
substrate, added either four tadpoles or two crayfish to treatment tanks, and measured predation
after a set time period. We used eggs in control tanks to determine if we could accurately count
eggs after 72 hours or if they disintegrated beyond recognition; this occurred to one egg in 1 of 6
control tanks used in these egg predation trials. During the experiment we provided tadpoles and
crayfish with alternative food sources, including lettuce, bloodworms, and live and frozen brine
shrimp. Razorback eggs were obtained from Willow Beach hatchery. We originally planned to
run both trials for 72 hours. However, crayfish consumed the eggs rapidly, so in order to obtain
instantaneous predation rates we ended these trials after six hours of exposure.

Egg predation experiments were conducted from 15-18 March (Table 1). Both species consumed
razorback eggs; predation averaged 74% for crayfish and 45% for tadpoles. In terms of
instantaneous predation rates, tadpoles consumed a mean of 0.03 eggs per tadpole per hour
(Table 2). Crayfish were more voracious, eating on average 1.1 eggs per crayfish per hour.

Lan-al Predation Experiments-Experiments on razorback larvae ran from 15-30 March 2004.
We tested predation capability of bullfrog tadpoles; young-of-year green sunfish, carp, and
channel catfish; and adult threadfin shad (Dorosomapetenense) and fathead minnow
(Pimephales promelas). All species that we tested consumed razorback sucker larvae. Mean
mortality of larvae ranged from ,::::10% in tanks with tadpoles, threadfin shad, and fathead
minnows, and 2:.70% for carp, green sunfish, and channel catfish. There was no consistent
relationship between gape size and consumption rate (Table 1). Mortality in the ten larval control
tanks was insignificant: one larvae died in a carp trial and one in a tadpole trial.
Compared to the other predator species used in 2004, bullfrog tadpoles were one of the largest
predators tested, in terms of both total length and biomass (Table 1). However, the tadpoles had a
small gape relative to their size, and they ate relatively few larvae. Their instantaneous predation
rates were nearly identical to threadfin shad and fathead minnows (Table 2). Threadfm shad is

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