OTTAWA CITIZEN (Ontario) 31 July 03 There are no big, stupid bullfrogs (Jean Levac)
Natural Resources staff headed out to the shores of Mississippi Lake earlier this week to measure the frog population. Bruce Ward tagged along and explains why their work is important to the preservation of the area's amphibians.
It's nearly 9 p.m. and getting dark. This is the hour when male bullfrogs begin chorusing to attract mates, which is why biologist Chris Burns, net in hand, is standing aboard an airboat in the middle of a marsh.
Chris is at work on the annual bullfrog monitoring project carried out by the Kemptville district of the Ministry of Natural Resources, and Citizen photographer Jean Levac and I hitched a ride with him on Tuesday to get an up close look at the job.
The airboat is slowly skimming along the shoreline of McEwen Bay on Mississippi Lake, about 12 kilometres west of Carleton Place on Highway 7. The frogs could be singing an aria from Puccini's Tosca for all I know. The only sound I hear through my ear protectors is the roar of the airboat's engine. I can see a wall of insects off the bow, lit up by the boat's floodlights. I can see reeds, lily pads and rotting vegetation. What I can't see is any frogs.
Yet Chris has already netted seven frogs with the help of senior fish and wildlife technician Greg Borne, who is piloting the airboat.
The frogs are naturally wary, says Greg. "You don't get to be a big bullfrog by being stupid," he jokes. However, the bright lights and noise from the airboat can daze the frogs, making them easier to catch.
Sometimes Greg sees them first, which is amazing considering he's also watching for rocks and stumps protruding from the water -- less than a metre deep in the marsh. The airboat has no brakes or reverse gear, which can be a little tricky. It's powered by a car engine, which turns an aircraft propeller mounted directly behind Greg at the rear of the boat.
On the boat, the captured frogs are placed in containers according to size. "If you put big frogs and small frogs together, pretty soon you only have big frogs," says Greg. "I've pulled little frogs out of the jaws of a bigger one."
Back on shore, three other ministry employees -- Paula Norlock, Colin Langford and Tanya Murrant -- help catalogue the frogs, which are weighed and measured. The sex of each bullfrog is also noted by examining the tympanum or ear, a circular patch just above its front legs.
"You can generally tell if it's male or female by looking at the ear," explains Chris. "If the tympanum is larger than the frog's eye socket, it's male. If it's the same size or smaller, then the frog is female."
The frogs have a lifespan of about 10 years. They grow slowly, taking about four years to reach 18 centimetres.
The frogs are marked by getting a sort of scientific manicure from Colin. First, he dips one of the frog's toes in a cream, which freezes it temporarily. Using special scissors, he then clips off a tiny piece of its toe. The frog is not harmed. This is done so in future the bullfrogs can be identified as being previously captured.
The frogs are later released near the area where they were captured.
The team will work until 2 a.m., by which time they will have caught, marked and released about 40 bullfrogs.
Although mosquitoes are out in droves, none of them is wearing insect repellent. "If we did use bug spray, the frogs could absorb it through their skin, which is harmful," says Chris.
The team also monitors bullfrogs on the Tay Marsh in Perth as part of the ministry's long-term program. On both sites, Chris says, the bullfrog population appears to be declining over the past three years.
"This is really a global concern and there are many factors involved. The eggs, which are laid near the surface of the water, can be damaged by ultra-violent light, which is increasing because of the depleting ozone layer.
"There's also pollution and pesticides and their predators, including blue herons, and, of course, man."
People living near the marshes have reported fewer bullfrogs calling in the spring over the last few years, he says.
"But population fluctuations also occur naturally. The best way to determine population is to follow trends through time, and that's what we're doing."
There are no big, stupid bullfrogs