UVIC researcher studies B.C. bullfrog invasion
Big, green, bug-eyed aliens with huge appetites are invading southern Vancouver Island.
You can see -- and hear -- the invasion happening in several lakes and ponds around Victoria, Duncan, Nanaimo and Parksville this summer. The intruder is the American bullfrog, and 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 UVic 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, including Victoria's Elk and Beaver Lakes.
Govindarajulu says the evidence is mounting that bullfrogs are supplanting native frog species. "Once bullfrogs get established they pretty much clean out the competition," notes Govindarajulu, who frequently gives public talks -- through the UVic Speakers Bureau and the Capital Regional District's naturalist program -- on ways to minimize the impact of this impressive, but unwelcome amphibian.
"The easiest thing we can do is not move frogs around, which people still do, especially now that aquatic gardens and backyard ponds have become so popular," she says. "Wild frogs aren't going to stay in your backyard, they're going to hop away."
Although Govindarajulu releases the bullfrogs she captures in her study lakes, she will euthanize frogs discovered in new areas. Some people have difficulty understanding this, she says. "They get very irate and say I'm playing God, but my answer is that we've already played God. Bullfrogs don't belong here and they're endangering our native frogs. It's important to make that distinction."