Invasive African clawed frogs (Xenopus laevis) in Washington State: status, response efforts, and lessons learned

Eveline J Emmenegger¹Rebecca A Lavier^2,3Emily J Struck^4,5Vasilisa P Tyurina⁴Evan A Eskew^4,6Megan R Friesen^7,8Mark A Taylor²Emma K Bueren^1,9David R Kyle¹⁰Jesse M Schultz¹¹Allen Pleus¹¹Richard H Visser Ii¹¹Reed Ojala-Barbour¹¹Christopher D Anderson¹¹Jeffrey S Jensen¹²Martha Keller^13,14Thomas S Jenkinson¹⁵Katherine Haman¹¹Tony R Capps¹¹Kenneth I Warheit¹¹Timothy Quinn¹¹Justin Bush¹¹Max R Lambert^11,16*

• ¹Western Fisheries Research Center, United States Geological Survey (USGS), Seattle, United States
• ²Three Rivers Chapter, Trout Unlimited, Issaquah, WA, United States
• ³College of Fisheries and Ocean, University of Alaska Fairbanks, Fairbanks, Alaska, United States
• ⁴Pacific Lutheran University, Tacoma, Washington, United States
• ⁵Purdue University, West Lafayette, Indiana, United States
• ⁶University of Idaho, Moscow, Idaho, United States
• ⁷Saint Martin's University, Lacey, Washington, United States
• ⁸Wenatchee Valley College, Wenatchee, Washington, United States
• ⁹Indiana University, Bloomington, Indiana, United States
• ¹⁰Lake Washington Basin Program, Trout Unlimited, Issaquah, Washington, United States
• ¹¹Washington Department of Fish and Wildlife, Olympia, Washington, United States
• ¹²University of Washington Bothell, Bothell, Washington, United States
• ¹³Southwestern Native Aquatic Resources and Recovery Center, United States Fish and Wildlife Service, United States Department of the Interior, Dexter, Michigan, United States
• ¹⁴US Department of Agriculture, Kansas City, Missouri, United States
• ¹⁵California State University, East Bay, Hayward, California, United States
• ¹⁶The Nature Conservancy in Washington, Seattle, Washington, United States

The African clawed frog (ACF, Xenopus laevis), which is indigenous to sub-Saharan Africa, is an aquatic invasive species known to have severe ecological impacts on native fauna when introduced into non-endemic regions. In 2015, ACFs were detected in Washington State, U.S. for the first time, and the species is now documented at three cities across western Washington: Lacey, Bothell, and Issaquah. We catalogued the known ACF occurrences, early management efforts, biological data about the frogs, and status of these invasive populations at the three sites from 2015-2023. The ACFs appear to be established in at least three watersheds in the Puget Sound region despite substantial effort at eradicating them at one site. Presence of ACFs in watersheds that lack surface connectivity implies independent introduction events, and the capture of frogs in multiple subbasins in the same watershed may reflect the potential for further spread. Because the ACF is nocturnal and otherwise behaviorally and visually highly cryptic, other established populations may go undetected. Where the ACFs are largely confined to stormwater ponds -as many of our current observations suggest -eradication may still be possible, though a substantial, focused effort would be required. In addition, significant refinement of eradication approaches will be needed to ensure effectiveness in topographically and vegetatively complex Pacific Northwest aquatic environments.