Movement, Habitat, and Home Range of Introduced Bullfrogs (Lithobates Catesbeianus) on Mad River Gravel Ponds (Humboldt Co., CA, USA), With Implications for Hydro-Modification as a Method of Management

American Bullfrogs are a non-native, invasive species in California (USA), where they are known to have deleterious effects on many native species. Carnivorous adults prey on native amphibians and fish, while herbivorous tadpoles outcompete native tadpoles for algal food resources. Bullfrogs have been successful at colonizing old tailing ponds and other pools left over from mining activities, and these relict pools are common on many rivers in California. Information on the dispersal capabilities of Bullfrogs could help predict range expansions and inform management decisions. Unfortunately, this information is lacking from both their native and invaded range. From May to August of 2015, I used radio telemetry to track 29 Bullfrogs located in two gravel extraction sites (164 m apart) on the lower Mad River in western Humboldt County, CA. Four frogs (14%) switched between the two ponds over the three-month tracking period. I did not observe any frogs using the river channel or nearby seasonal wetlands. The mean home range size was 1600 square meters and did not differ by sex or age class. As a removal effort, both ponds were partially filled with gravel in September 2015 under the direction of the California Department of Fish and Wildlife (CDFW). In the following year, populations of Bullfrogs did not return to the survey area, even when the hydro-modified sites contained water, or when off-channel pools were present in the vicinity. Based on the timing of breeding and metamorphosis, as well as the lack of summer movements observed in this study, pond filling may be most effective as an eradication tool between the culmination of egg laying and the end of metamorphosis