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An Amphibian Community After Fish Removal: A Tale of Four Ponds
Lee M. Gross and Stephen J. Mullin
Department of Biological Sciences, Eastern Illinois University.
Introduction
Habitat loss and fragmentation are important contributors
to population declines in many species. Maintaining suitable habitat has
become a priority for managing several amphibian species. The introduction
of predatory fish can alter amphibian communities structure (1,4,7).
Removing introduced fish can help restore suitable habitats for individual
amphibian populations (8), but long-term assessments of such removals are
lacking at the community level in the literature.
RotenoneTM is used commonly in fisheries management for the eradication of
exotic and introduced fish (5). The most effective application time for
RotenoneTM is in late fall or winter, when amphibians are not active, to
limit the impact on non-target organisms, and yet remove introduced fish.
Objective
1. Determine the impact of fish removal on an amphibian community.
A. Determine changes in community
structure
B. Determine changes in larval
recruitment
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Rana sylvatica |
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Rana catesbeiana |
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Ambystoma texanum |
Methods
Warbler Woods Nature Preserve (81.5 ha) contains secondary oak-hickory forest,
old agricultural fields with tree seedlings, and four ponds (3 permanent ponds,
and 1 ephemeral pond; labeled A,B,C, and D, respectively).
Drift fences with pit-fall traps were constructed around the majority of each
pond. Since May 2000, traps were monitored every 48 hours, from mid-February to
late-November.
Individuals collected from the traps were measured (snout-vent length [±1 mm],
tail length [±1 mm]), toe-clipped by cohort, and released.
RotenoneTM was applied in Ponds B and C in 2002 (Year 3) to remove fish, and
again in Pond B (Fig. 1) in 2003 (Year 4).
T-tests with a BACI design (6) were used for statistical analysis to test each
species’ abundance before and after fish removal in each pond.
An ANOVA was used to determine changes in juvenile recruitment pre and post fish
removal.
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Figure 1: RotenoneTM application in
pond B |
Results
Fish Removal Summary For Each Pond
Ponds A and D: Never contained fish (D is ephemeral, going dry on or before
August 2).
Pond B: Black Bullhead catfish (Ameiurus melas) removed after the third year.
Pond C: Bluegill (Lepomis macrochirus) & green sunfish (Lepomis cyanellus)
removed after the second year
The BACI analysis indicated differences in A. texanum abundance for pre- and
post-fish removal periods in ponds A and B (T = -2.78, P = 0.04), as well as
ponds A and D (T = -2.75, P = 0.04).
Juvenile recruitment in A. texanum was greater in mitigated ponds after fish
removal (F1,12 = 5.73, P = 0.034).
There were no differences between any pond combinations in all other species.
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Figure 2: The proportional species abundance for each of the four ponds,
for all seven years. Bufo fowleri, Acris crepitans, and Pseudacris
triseriata are represented by the “others” category. The red arrow
represents when the applications of RotenoneTM occurred. Years 1 and 7
comprise of partial data sets. |
Discussion
Amphibian populations are known to naturally
fluctuate through time.
Only A. texanum populations increased following fish removal. Other species
also exhibited trends in population fluctuation as a function of treatment type
(Fig. 2), even though these were not significant.
It is unlikely that all the changes experienced by each species were due to
natural population fluctuation. Fish had an influence on the amphibian community
before their removal.
Prey species such as B. americanus and R. catesbeiana are avoided by fish
(either due to unpalatability or predator gape limitation; 3,4,7). Both R. catesbeiana and
B. americanus were dominant in ponds B and C when fish were
present, but have diminished in abundance since the fish were removed (Fig. 2).
Other species – A. texanum, R. sylvatica, P. crucifer, and
H. versicolor – are
palatable to fish (3,4,7), and have increased their proportional abundance since
fish were removed (Fig. 2).
Recruitment of larval smallmouth salamanders improved in the 2 years following
fish removal; we suspect that similar improvements were experienced by other
amphibian species, except for B. americanus which is an inferior competitor at
the larval stage.
We do not believe that RotenoneTM had any negative impact on the amphibian
community due to the fact that R. catesbeiana tadpoles were still present at
time of application.
RotenoneTM is an effective way to remove fish from amphibian breeding habitat,
especially in situations where continued monitoring of its long-term effects is
possible.
References
1.
Baber & Babbitt, 2003, Oecologia 136:289-295.
2.
Chandler, 1982, Progressive Fish Culturists 44:78-80.
3.
Kats et al., 1988, Ecology 69:1865-1870.
4.
Kurzava & Morin, 1998, Ecology 79:477-489.
5.
McClay, 2000, Fisheries Management 25:15-21.
6.
Parker, 1986, Ecology 67:929-940.
7.
Smith et al., 1999, Freshwater Biology 41:829-837.
8.
Vredenburg, 2004, PNAS 101:7646-7650.
Acknowledgements
We thank the Illinois Department of Natural Resources for funding various
portions of this project. Special thanks goes to B. Bostrom, T.
Buhnerkempe, M. Diana, M. Fincel, A. Fornell, M. Olds, C. Powell, B. Towey,
D. Foster, and L. Walston for all their assistance in the field and
collecting data.
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