9638

• UCREFRP Catalog Number: 9638
• Author: Mueller, G. A., J. Carpenter and D. Thornbrugh
• Title: Bullfrog Tadpole ‎(Rana Catesbeiana)‎ And Red Swamp Crayfish ‎(Procambarus ClarkII)‎ Predation On Early Life Stages On Endangered Razorback Sucker ‎(Xyrauchen Texanus)‎
• USFW Year: n.d.
• USFW - Doc Type: The Southwestern Naturalist
• Copyright Material: YES

June 2006 Notes 259
T,',R1,E I-Size of prey mid predator's (diameter of fish egg, total length of fish larva and tadpole, and
cephalothorax length of crayfish) and predation rates (number of individuals consumed/day) of bullfrog
(Rana catesbeiana) tadpoles and red swamp crayfish (Procarnbarus clarkii) preying on razorback sucker (Xy-
rauchen texanus) eggs and larvae in laboratory tank experiments.

Test Prey size (mm)
mean (range) Predator size (mm)
mean (range)
Tests n Number consumed
mean (95% CL,)
Egg-Tadpole 3.2 (2.7-3.5) 100 (84-116) 6 2.2 (12-2.9)
Egg-Crayfish 3.2 (2.9-3.5) 32.8 (26.3-40.6) 8 6.0 (2.7-9.4)
Larvae-Tadpole 11.5 (10,1-12.5) 100 (83-115) 7 1.4 (0.8-2.0)
Larvae.-Crayfish 18.5 (1.3.3-27.6) 48,5 (33.9-65.4) 12 3.5 (1.9-5.1)
Controls
Eggs 3.2 (2.7-3.5) 10 NA
Larvae 15.0 (10,1-27.6) 10 0.1 (0.0-0.3)
Mortality only
covered in a tub where razorback sucker were
held prior to data processing were used in a
preliminary experiment, rather than being dis-
carded. One hundred eggs were put into each
of 4, 38-L, aerated aquarium tanks in the lab-
oratory. Subsequently, 25 bullfrog tadpoles
were added to each of 3 tanks, leaving one
tank holding only fish eggs. The tanks were al-
lowed to sit unattended over the weekend and
were examined after 72 h. The fish eggs were
completely absent in tanks containing tadpoles
and were all present in the control tank.
Based on these preliminary results, we de-
signed a more structured and expanded series
of tests to examine whether bullfrog tadpole
and crayfish would eat razorback sucker eggs,
larvae, and fry. Additional bullfrog tadpoles
and crayfish were collected from Cibola HLP,
and razorback sucker eggs, larvae, and fry were
provided by Willow Beach National Fish Hatch-
ery. Experiments were conducted in 38-L, aer-
ated aquariums that were equipped with sepa-
ration screens that initially isolated predators
front prey. Substrate and cover were not pro-
vided to allow accurate counts of the number
of eggs and larvae remaining after a 24-h ex-
posure experiment. .
Tanks contained either 4 tadpoles, 2 cray-
fish, or no predators (control) and 20 razor-
back sucker eggs or larvae. Controls were used
to measure natural mortality of larvae and vis-
ibility or deterioration of eggs, because these
factors could influence consumption rates.
The number of tests and size of test organisms
was dictated by their availability. Shortages of
larvae made it necessary to use larger (>14
mm) fry for some crayfish experiments. Pred-
ators and prey were measured for total length
(fish, tadpoles) and cephalothorax length
(crayfish) (Table 1). Separating screens were
gently removed to start the experiment, and
remaining prey were counted at the end of 24
h. These 24-h experiments indicated that, tad-
poles consumed an average of 2.2 eggs/d (n =
6 tests) and 1.4 larvae/d (n = 7 tests), while
crayfish ate an average of 6.0 eggs/d (n = 8
tests) and 3.5 larvae/d (n = 12 tests) (Table
1). Only 3 of 200 control fish died during the
experiments (n = 10 tests).
I field MonitMng-Sparv ling activities of ra-
zorback sucker and bonytail (Gila elegans), an-
other native fish found in the Cibola HL.P,
were recorded using underwater video equip-
ment. During this monitoring, bullfrog tad-
poles and crayfish were commonly observed
feeding among spawning fish. These filming
sessions were expanded to gain a better un-
derstanding of the relative abundance of bull-
frog tadpoles and crayfish among spawners.
Two 12-volt (VDC), black-and-white, under-
water video cameras were mounted on small
submersible tripods and aimed at the bottom.
These cameras were linked to surface monitors
and VHS recorders. Four areas were filmed: a
razorback sucker spawning area, a bonytail
spawning area, and 2 areas that were randomly
chosen that were not being used by spawners.
Recordings were reviewed using a VHS film ed-
itor and stopped at precise 5-minute intervals
to count tadpole and crayfish observed in that
single frame. Density estimates were calculated
from the number of organisms observed divid-