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Bullfrogs Invading Southern Vancouver Island

The American bullfrog is not native to Canada's west coast, but they can now be found in several lakes and ponds around Victoria, Duncan, Nanaimo and Parksville. Its distinctive bwum, bwum, bwum bass serenade is signalling big trouble for the Island's native frog species and aquatic ecosystems in general.

"The biggest problem is that bullfrogs eat other frogs. Actually, they'll eat just about anything," says University of Victoria graduate student Purnima Govindarajulu, who is studying the biology of the bullfrog invaders for her PhD. Insects, fish, snakes, small mammals and birds, even other bullfrogs, are all fair game. "Whatever they can fit into their huge mouths," she says.

To find out where the bullfrogs are, how fast they grow and what they're eating, Govindarajulu spends her summers stalking, catching, measuring and tagging her slippery subjects in Victoria-area ponds and lakes.
In Canada, bullfrogs are not naturally found west of Ontario. It was people - probably looking to enhance their aquatic gardens or farm frogs for their tasty legs - who brought the first bullfrogs to B.C.'s Lower Mainland and Vancouver Island several decades ago. The frogs have been spreading in leaps and bounds ever since.

"Their range on the Island is expanding by about five kilometres a year, mainly near urban areas," says Govindarajulu. So far, she's found them in several dozen local lakes and ponds.

Govindarajulu says the evidence is mounting that bullfrogs are supplanting native frog species. "Once bullfrogs get established they pretty much clean out the competition."