9488

• UCREFRP Catalog Number: 9488
• Author: Mueller, G. A., J. Carpenter, P. C. Marsh and C. O. Minckley.
• Title: Cibola High Levee Pond Annual Report 2003.
• USFW Year: 2003.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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rnm). We believe the larger fish were better at avoiding predators than their younger
cohorts.

There is ample evidence that crayfish can be effective competitors and predators of native
fishes (Minckley and Craddock 1961, Guan and Wiles 1997, Carpenter 2000). Crayfish
can be aggressive predators of fish eggs and juveniles (Horns and Magnuson 1981,
Savino and Miller 1991, Carpenter 2000). The tank tests supported previous literature.

These tests will be repeatednext year, using fish of the same size groups with complete
series of various sizes; hopefully we will also expand tests to include bonytail.

Table 5. Results of tanks tests examining predation rate of razorback sucker :fry by
crayfish in the presence and absence of protective cover.

Tank 1

Tank 2

Tank 3

Tank 4

Predation Loss

No Cover
Start
24 hours
48 hours
72 hours

(RZB length 16.2 rnm, crayfish 34 rnm)
20 20 20
20 4 6
20 0 0
20 0 0

20
15
5
3

0%
58.3%
91. 7%
96.7%

Deep Cover
Start
24 hours
48 hours
72 hours

(RZB length 16.1 rnm, crayfish 48.9 rnm)
19 20 20
19 20 16
19 13 10
19 9 4

20
16
6
5

0%
13.3%
35.0%
70.0%

Shallow Cover (RZB length 20.5 rnm, crayfish 54.7)
Start 20 20 20
24 hours 20 19 . 20
48 hours 20 18 18
72 hours 20 28 17

20
20
20
20

0%
1.7%
3.3%
8.3%

Potential Predators of Razorback Larvae. All tested predators consumed razorback
suckers. Larvae suffered 100% mortality in both rainbow trout tests; mortality was >85 %
in tanks with bonytail, red shiner, and yellow bullhead (Table 6). Bullfrog tadpoles and
Lepomis sp. (bluegill and/or redear <6 em) had low predation rates; this is likely due to
the smaller gape ofthese animals compared to other predators.

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