Bullfrogs Invading Southern
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."