American bullfrog management on Vancouver Island Errico, Claire
The American bullfrog (Lithobates catesbeianus) is an invasive amphibian native to the eastern region of North America that is now located throughout the south west coast of British Columbia due to ill-fated frog’s legs operations. Brought to Vancouver Island in the 1930’s, the American bullfrog has spread throughout the south island and threatens to establish in the Greater Victoria Water Supply Area causing concern among the area’s management team in regards to the impacts on water quality and native ecology. Proposed management strategies include eradication, habitat modification, education, and increased water treatment through filtration. There is very little information on the public health and turbidity impacts of the American bullfrog. There is no information on how high densities affect turbidity in their native range and in areas where they have established as invasive species. Much of the research on pathogens carried or distributed by the American bullfrog that is available is vague and is not directly tied to human health. There is preliminary research available that suggests that the American bullfrog can act as a carrier for E.coli., but that research has yet to progress further than controlled tests in well controlled situations. From a water quality perspective, there is not enough information at this point to justify management of the species. Little work has been done, likely because it is not seen as a threat to water quality parameters in its native range. However; ecologically, current research strongly suggests that the American bullfrog has a negative impact on the growth and development of the pacific tree frog (Pseudacris regilla) and the blue-listed northern red legged frog (Rana aurora) but these impacts may be mitigated through habitat modification (Govindarajulu, 2004). Due to the complex relationships between invaders and indigenous environments the biggest risk associated with bullfrogs on southern Vancouver Island is the potential for a trophic cascade of unknown impacts on ecosystem services if bullfrogs were to eliminate or severely reduce the population numbers of indigenous species. From the perspective of a responsible land and resource management, this threat to native species and predator-prey systems is enough to justify management of the species, especially regarding the vulnerable classification of the red-legged frog. Of the management options available, the recommended method is a combination of habitat modification, bullfrog population control, and education to protect native species and ecosystems and to prevent further dispersal of the species. Complete eradication and filtration treatment plants are not necessary at this point without solid information on the impacts of the species. The existing infrastructure and treatment regime of chlorination and UV treatment is sufficient to kill or neutralize any pathogenic or bacterial threat that may emerge as a result of bullfrog establishment within the watershed.
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