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260 The Southwestern. Naturalist vol. 51, no. 2
<br />ed by a size estimate of the viewing area (the
<br />viewing area varied due to camera angle). Av-
<br />erage densities were multiplied by the total
<br />area of the pond to develop a simple estimate
<br />of population size.
<br />Twelve video sessions (2 h each) taken dur-
<br />ing daylight hours from 18 February to 17
<br />April 2003 were analyzed for the presence of
<br />bullfrog tadpoles and crayfish. Bullfrog tad-
<br />pole densities (n = 286 frames) averaged 2.1
<br />tadpoles/m2, with densities increasing (0.9 to
<br />3.7 tadpoles/m2) during the course of the
<br />study. Adult crayfish densities averaged <0.1
<br />crayfish/m2 (0.0 to 11.1 crayfish/m2) during
<br />the same period. The tadpole and crayfish
<br />community was estimated at approximately
<br />>48,000 tadpoles and >2,000 crayfish.
<br />Given that bullfrog tadpoles and crayfish
<br />consumed razorback sucker eggs and larvae
<br />under laboratory conditions, their abundance
<br />and presence among spawners at Cibola HLP
<br />suggests they might pose a threat to native fish
<br />eggs and larvae if their densities are relatively
<br />high. The intermittent recruitment of razor-
<br />back sucker at Cibola HLP might be attribut-
<br />able to bullfrog tadpole and crayfish preda-
<br />tion, because nonnative fish predators were
<br />rare (<O.I % of the 3,760 fish sampled) (Muell-
<br />er et al., 2005).
<br />Introduced bullfrogs and crayfish are wide-
<br />spread and abundant not only in the wild, but
<br />also in many culturing facilities (Bills and
<br />Marking, 1988; Kane et al., 1992). Bullfrog tad-
<br />pole predation of eggs and larvae of native an-
<br />urans and salamanders is well documented
<br />(Ehlrich, 1979; Kiesecker and Blaustein, 1997;
<br />Murray et al., 2004), but their threat to native
<br />fish is less recognized (Kane et al., 1992). Boyd
<br />(1975) suspected tadpole predation on fish,
<br />but Nguenga et al. (1997, 2000) were the first
<br />to document and measure toad (Bufo regulatis)
<br />tadpole consumption (17 fish/d) of African
<br />catfish (Heterobranchus longifilis). They found
<br />fish larvae were most vulnerable prior to de-
<br />veloping fins (<6 d).
<br />Crayfish predation on eggs of recreational
<br />and native fishes is well documented (Horns
<br />and Magnuson, 1981; Dorn and Mittelbach,
<br />2004). Evidence of crayfish feeding on live fish
<br />larvae is less common. In laboratory settings,
<br />crayfish fed on young lake trout (Salveninus na-
<br />maycush; Savino and Miller, 1991) and juvenile
<br />Gila chub (Gila intermedia), suckers (Catosto-
<br />mus), and speckled clace (RltinichthTS osculus)
<br />(Carpenter, 2000). Gut content analyses pro-
<br />vided evidence of P clarkii consuming Garnbu-
<br />sia in a freshwater marsh (Gutierrez-YLirrita et
<br />al., 1998). Introduced crayfish negatively im-
<br />pacted several benthic fish communities in
<br />British rivers via competition and predation
<br />(Guar and Wiles, 1997).
<br />Predator removal programs aimed at restor-
<br />ing razorback sucker recruitment. within the
<br />Colorado River basin have typically focused on
<br />the removal of large, nonnative fish predators
<br />(Mueller, 2005). When large predators that de-
<br />press nontraditional predators (i.e., preda-
<br />ceous insects, crustaceans, and amphibians)
<br />are removed, the latter typically increase in
<br />abundance (Horn et al., 1994; Mueller and
<br />Burke, 2005). These cause-and-effect reactions
<br />deserve closer scrutiny in predator control
<br />programs, because of the potential negative ef-
<br />fects the nontraditional predators might pose
<br />to the early life stages of fish.
<br />LITERATURE CITED
<br />Bius, T. D., AND L. L. MARKING. 1988. Control of
<br />nuisance: populations of crayfish with traps and
<br />toxicants. Progressive Fish-Culturist 50:103-106.
<br />BOYD, S. H. 1975. Inhibition offish reproduction by
<br />Rana catesbeiana larvae. Physiological Zoology 48:
<br />225-234.
<br />CARPENTER, J. 2000. Effects of introduced crayfish on
<br />selected native fishes of Arizona. Unpublished
<br />Ph.D. dissertation, University of Arizona, Tucson.
<br />DORN, N. J., AND G. G. MITTEL11ACIL 2004. Effects of
<br />a native crayfish (Orcon.ectes viriti.s) on the repro-
<br />ductive success and nesting behavior of sunfish
<br />(Lelvniis spp.). Canadian journal of Fisheries and
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<br />vae of the plains leopard frog (Rama blahi). Bul-
<br />letin of the Maryland Herpetological Society 15:
<br />25-26.
<br />GUAM, R. "Z., AND P. R. WILES. 1997. Ecological impact
<br />of introduced cravfish on benthic fishes in a Brit-
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<br />GUTIERREZ-YURRITA, P. J., G. S Nciio, M. A. BRovo, A.
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<br />red swamp crayfish Procambarus clarkii in natural
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<br />rary fresh-water marsh (Spain). Journal of Crus-
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<br />HORN, M. J., P. C. MARSH, G. MUELLER, AND T. BURKE.
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