The Spread, Effect and Mitigation of Bullfrogs in the Western United States

1. The Spread, Effect and Mitigation of Bullfrogs in the Western United States Jennifer Spawn SWES 474 28 November 2006

2. The Origin of Bullfrogs • Bullfrogs are originally native to Europe • They were introduced to the Eastern U.S. • They are now considered “naturalized” • West of the Rocky Mountains they are still considered non-native

3. Where art thou, Bullfrog? • highly aquatic, but will use the land • migration • Found in both lentic and lotic freshwater environments • Mainly temperate and subtropical species • Like vegetation to hide in and lay eggs on

4. Ya’ll might make me act A’frog up in here • mostly nocturnal but are somewhat active during the day • Males are territorial • They will eat anything will fit in their mouths…including small children and pets • breathe through their skin

5. The Big, Bad Bullfrog • Bullfrogs have been in the West since the 1890’s • They were introduced as a sport animal • Because of their voracious appetite bullfrogs have been labeled a nuisance • They are out- competing the native anuran populations • With a decline in anuran populations already, natives are in much greater danger

6. A study by Hecnar and M’Closkey found a change in community composition in SE Canada As bullfrogs declined the native species flourished Interspecies competition was a factor A release of predation was found to be the leading cause of native species revival This study is the general consensus among biologists: bullfrogs are a negative keystone species in an ecosystem A study done by Hayes and Jennings indicates bullfrogs may not be the cause Habitat loss, fragmentation and pollution may also be factors Other predators may also be to blame Disease is also a major player Bottom line we really don’t have a clear answer…interspecific relationships are complex Are bullfrogs really that bad?

7. So what’s the deal here?(Arizona) • The native Ranid species in Arizona are all either threatened or are of special concern • In many areas native species are in direct competition with and predation by bullfrogs • However to say bullfrogs are the sole cause is irresponsible • Bullfrog populations are out of control in some areas

8. What’s the government doing? • The U.S. Fish and Wildlife Service is the main agency dealing with bullfrog effects • ESA • The Arizona Game and Fish Department also helps out • You can hunt bullfrogs if you want! • www.azgfd.gov

9. Specific Mitigation • Biological • Chemical • Mechanical • Integrated Pest Management

10. Biological Control • As of yet there is no really great biological control of bullfrogs • Large Mouth Bass, Diving beetles, Dragonfly larvae and water nymphs like to eat them • None species specific • But still, the bullfrog population is growing rapidly in some areas of the state

11. Chemical ControlRotenone • Rotenone is a chemical used primarily by fisheries • It does not allow cellular respiration • The electron transport chain is interrupted • Oxygen builds up in the blood and slows breathing until the animal dies • Adult bullfrogs do not have gills but diffuse oxygen across their skin…thus Rotenone should have an affect on adult bullfrogs

12. HOWEVER…it doesn’t !

13. Lessons from the San Rafael Valley • Rotenone was applied to kill bullfrogs • People were positioned around the tank to gig bullfrogs as they left the water • People were also positioned to rescue salamanders

14. Lessons from the San Rafael Valley • Rotenone although it breaks down by itself in about a week, must be neutralized with Potassium permanganate

15. Lessons from the San Rafael Valley • No bullfrogs were killed by Rotenone • We seined and put out traps and no bullfrogs were found dead • Frogs can also breathe using their mouths and lungs • However, if tadpoles were present they were certainly killed • The salamanders were harmed • It was expensive, smelly and inefficient compared to other methods

16. Mechanical or Physical Control Shooting Seining Hand Capture/Gigging Trapping

17. Seining

18. Hand Capture and Gigging • Frogs are pretty hard to catch during the day unless you have “frog eyes” and can sneak up on them • Hand capture at night with a flashlight is easier • The best way is to seine the frogs out of the tank or stream and either gig or smash them against a rock

19. Trapping • You can also use minnow traps to try and lure in frogs with some bait…

20. Integrated Pest Management • A combination of chemical and physical controls is the best solution • New technologies and solutions need to be pursued • More research about bullfrogs and their effects need to be done

21. In Conclusion… • Bullfrogs are a typical invasive species • They should not be made into this terrible monster • There needs to be a better way to control the population • Get a hunting license and go eat some frogs…you’ll help out wildlife all over AZ!

22. Sources • Clarkson, R.W., DeVos Jr, J.C. The bullfrog, Rana catesbeiana Shaw, in the Lower Colorado River, Arizona-California. Journal of Herpetology (20)1: 42-49. 1986 • Hayes, M.P., Jennings, M.R. Decine of ranid frog species in Western North America: are bullfrogs, Rana catesbeiana, responsible? Journal of Herpetology (20)4: 490-509. 1986 • Hecnar, S.J., M’Closkey, R.T. Changes in the composition of a ranid frog community following bullfrog extinction. American Midland Naturalist (137)1: 145-150. 1997. • Moyle, P.B. Effects of introduced bullfrogs, Rana catesbeiana, on the native frogs of the San Joaquin Valley, California. Copeia (1973)1: 18-22. 1973. • Roach, John. “Invading Bullfrogs Appear Nearly Unstoppable.” National Geographic News. 28 September 2004. <http://news.nationalgeographic.com/new/2004/09/0928_040928_bullfrog.html> 20 November 2006. • Ryan, M.J. The reproductive behavior of the bullfrog (Rana catesbeiana). Copeia 1: 108-114. 1980. • Spawn, J. Personal field notes pp.24-26. 18 July 2006.