The American bullfrog is on the world’s top 100 invasive species list and can now be found in several B.C. locations. While many of us have never seen an American bullfrog, they are easy to identify. They have olive to bright green backs and creamy white underbellies mottled with grey or dark markings. And they’re big. They are North America’s largest frog, growing up to 800 grams and 20 centimetres in length.
The American bullfrog was initially introduced into coastal British Columbia for human consumption as it is known for its meaty legs. This cuisine trend never took off in B.C., and farmers released the frogs into the wild. The bullfrog was also a popular household pet and a favourite for outdoor ponds due to its ease of adaptation to any water habitat. When unwanted, pet owners would release these frogs into ponds and wetlands. These innocent acts of release have contributed to the current environmental issue without knowing the impact it would have. In addition, there have been bullfrogs that have migrated from Washington state into the Kootenays.
In 2015 a newly detected colony was found in the Kootenay region near Creston and reports are indicating they are spreading north. Vancouver Island, the Lower Mainland and the South Okanagan are also reporting colonies. In these new environments, bullfrogs lack their usual predators, like snapping turtles, to keep the population in check. These frogs also release an unpalatable toxic chemical from their skin, protecting them from predators.
While they prefer warm, weedy ponds or lakes, unfortunately they can also thrive in human-disturbed habitats. They are frequently found in ditches and slow-moving streams. These frogs can migrate up to 19 kilometres per year, contributing to the province’s invasive spread.
American bullfrogs can also transfer an infectious disease called chytrid fungus. The fungus thrives in cool, moist environments and feeds on living amphibians. The fungus consumes the keratin in the frog’s skin, causing it to thicken, preventing normal respiration. This fungus is directly responsible for declining amphibian populations. The bullfrog seems to be immune to the fungus.
The difference between the bullfrog and a native frog is that the bullfrog is larger and will eat almost anything that can fit in its mouth. The American bullfrog is an opportunistic predator and ambushes its prey. They are carnivorous and will eat amphibians, fish, rodents, snakes, turtles, songbirds, ducklings, and even each other. Evidence shows that new and increasing bullfrog populations are drastically affecting native and endangered frog species such as the northern leopard frog, the protected Pacific chorus frog, and Columbia spotted frog. They will either eat these protected species or their food.
Bullfrogs reproduce ten times faster than native frogs; therefore, the native frogs are being pushed out of preferred habitats. This is resulting in declining numbers of native frogs which is negatively impacting the ecosystem. These native frogs are an integral part of our ecosystem and food web. The smaller native frogs consume large amounts of insects and their tadpoles eat algae, which keeps waterways clean. These frogs and tadpoles are also an essential food source to predators such as dragonflies, fish, snakes, birds, beetles, and centipedes.
The Central Kootenay Invasive Species Society (CKISS) is just one group that is working to reduce American bullfrog populations. Last year CKISS safely removed many of these invasive frogs along the Kootenay River.
We can all do our part by not possessing, breeding, shipping, or releasing America bullfrogs in B.C. It is also important to not transfer tadpoles of any kind or to stock ponds with frogs from pet stores. When creating an outdoor pond, set up an attractive environment with water, shelter and insects to attract native frog species. Most importantly, raise awareness to avoid further spread into B.C.
Tara Gleboff is a second year Recreation, Fish and Wildlife students at Castlegar’s Selkirk College.