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Effects of nonnative fish on aquatic communities in small streams in the southwestern U.S.
Hall, David*,1, Steidl, Robert1, 1 University of Arizona, Tucson, Arizona
ABSTRACT- Introductions of nonnative fishes have had a range of adverse effects on native fish populations and likely has adverse effects on the entire aquatic vertebrate and invertebrate communities. We quantified the influence of nonnative fish on the abundance of aquatic macroinvertebrates and vertebrates in southeastern Arizona streams. We sampled during late spring, summer, and early fall 2001 to compare characteristics of aquatic organisms in two streams with nonnative fish and four streams without fish. We found relative abundance of macroinverterates to be three to six times higher in sites with no fish. In late summer, for example, relative abundance (mean no. individuals per sweep ± SE) of macroinvertebrates was 24 ± 3.5 in streams without fish compared to 7.6 ± 3.7 in streams with fish. Patterns for vertebrates were similarly strong. Leopard frog (Rana yavapaiensis) tadpoles were completely absent in sites with fish despite the presence of nearby source populations whereas in sites without fish relative abundance (mean no. tadpoles / trap day ± SE) was 0.6 ± 0.2. Relative abundance of tree frogs (Hyla arenicolor) was also lower in streams with nonnative fish. In late spring, for example, streams without fish had lower relative abundances (mean no. frogs observed/survey ± SE) of 9.4 ± 3.0 than streams with fish (1.4 ± 4.0). There were also other differences besides changes in abundance associated with the presence of nonnative fish. For example, size distributions of mud turtles (Kinosternon sonoriense) differed between streams with and without nonnative fish. Specifically, streams with fish had fewer fully grown turtles and fewer hatchlings. Further, streams with fish had a 10% fewer juvenile turtles than streams without fish. Because these aquatic systems are relatively small and discrete, restoration by effective removal of the nonnative fish is likely a feasible strategy.
KEY WORDS: nonnative fish, aquatic communities, aquatic macroinvertebrates, Rana yavapaiensis