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Jeff P_ 6- <br />258 <br />The Sbuthurestern. Naturalist <br /> <br />vol. 51, no. 2 <br />BULLFROG TADPOLE (RANA CATESBEIANA) AND RED SWAMP <br />CRAYFISH (PROCAMBARU.S CLARKin PREDATION ON EARLY LIFE <br />STAGES OF ENDANGERED RAZORBACK SUCKER <br />(XYRA UCHFN TEXANU.S) <br />GORDON A. MUELLER,* JEANETTE CARPENTER, AND DARREN Tt 1ORNBRUGH <br />United States Geological Survey, Box 250071)-8220, Denver, CO 80225 (GAM) <br />United States Geological -Survey, Fort Collins Research Center, 21.50 Centre Avenue, Building C, <br />Fort Collins, CO 800526 (JC) <br />Kansas State University, Division of Biology, 232 Ackert Hall, Manhattan, KS 66506 (DT) <br />*Correspondent: Gordan--LAluellerCusgs.gov <br />ABSTRacT-Bullfrog tadpoles (Rasta catesMana) and red swamp crayfish (T'vcartibarrrs clw-kii) are <br />widespread introduced taxa that are problematic throughout the western United States. Their <br />impact on native amphibians and crustaceans is well documented, but less is known regarding <br />their influence on native fishes. Predator-prey tank tests showed both species consumed eggs and <br />larvae of the endangered razorback sucker (Xyrauchen texanus) in a laboratory setting. Tadpoles <br />consumed 2.2 razorback sucker eggs/d and 1.4 razorback sucker larvue/d, while crayfish ate 6.0 <br />eggs/d and 3.5 larvae/d. Relatively high densities of bullfrog tadpoles and crayfish in razorback <br />sucker spawning areas suggest that these nonnative taxa might pose a threat to the recruitment <br />success of this and other imperiled native fish. <br />RcsustEN-Los renacuajos de la rana toro (Rana ca.tesbeiana) y una especie de cangrejo de rio <br />(Procambarus clarhii) son taxa no nativos problematicos con una distribuci6n geografica amplia en <br />el oeste de los Estados Unidos. Su impacto sobre anfibios y crustaceos nativos esta bien documen- <br />tado, pero su influencia sobre peces nativos es casi desconocida. Pruebas en tanques de depre- <br />dador-presa mostraron que ambas especies consumieron huevos y larvas del matalote jorobado <br />( `yrauchen texanus), una especie amenazada. Los renacuajos consumieron 2.2 huevos de X. tex- <br />an.us/dia y 1..4 larval/dia, mientras los cangrejos comieron 6.0 huevos/dia y 3.5 larvas/dia. Las <br />densidades relativamente altar de los ranacuajos de I1. catesbeiana y P. clarkii en zonas del desove <br />de X. texanus sugieren que estas especies no nativas tal vez sean una amenaza al exit.o de reclu- <br />tamiento de este y otros peces nativos amenazados. <br />Razorback sucker (Xyrauchen texanrts) is en- <br />demic to the Colorado River. Dramatic de- <br />clines in their number and range caused it to <br />be federally listed as endangered in 1991 (56 <br />FR 54957). The absence of young in the wild <br />has been attributed to predation by nonnative <br />fish (Minckley et al., 1991; Tyus and Sanders, <br />2000; Minckley et al., 2003). Recruitment levels <br />necessary to sustain populations have only oc- <br />curred in recent years in isolated ponds where <br />nonnative fishes are absent (Minckley et al., <br />1991; Minckley et al., 2003; Marsh and Pacey, <br />2005). <br />Cibola High Levee Pond (Cibola HLP) is a <br />2.3-ha human-made oxbow located on the low- <br />er Colorado River along the Arizona-Califor- <br />nia border and represents one isolated loca- <br />tion where sustainable recruitment has oc- <br />curred; however, survival of young razorback <br />suckers is intermittent. Nonnative fish are rare <br />(Mueller et al., 2005), suggesting other pred- <br />ators or factors might be responsible for the <br />periodic absence of young fish. For instance, <br />Horn et al. (1994) illustrated that razorback <br />sucker larvae are highly susceptible to odonate <br />nymphs and suggested they might also be vul- <br />nerable to other nontraditional predators. Our <br />discovery of bullfrog (Puma catesbeiana) tad- <br />poles and red swamp crayfish (Procambarus dar= <br />kii) among spawners prompted our curiosity <br />whether these introduced taxa could also <br />threaten early life stages of native fishes. <br />Laboratory Testsa-Large numbers of bullfrog <br />tadpoles and sexually ripe razorback suckers <br />were collected at Cibola HLP during routine <br />sampling in 2003. Several hundred eggs dis-