Raising Cain: Notorious cane toads invade Sanibel

10:22 AM, Aug 20, 2013   |    comments
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Sanibel, Florida (News-Press) -- One of the world's worst invasive non-native species has invaded Sanibel, and it's probably on the island to stay.

During a frog-call survey last month, herpetologist Chris Lechowicz of the Sanibel-Captiva Conservation Foundation heard the slow, low-pitched breeding call of cane toads.

Following the sound, Lechowicz found cane toads breeding in a temporary wetland near Middle Gulf Drive and Fulgar Street - these were the first cane toads documented on Sanibel.

"I was very surprised," Lechowicz said. "Cane toads are one of the things the biologists always said they never wanted to see here."

Natives of Central and South America, cane toads were introduced into Florida in the 1930s and 1940s to control sugar cane pests.

Those introductions failed, but the species became established and became a pest on Florida's southeast coast after the accidental release of about 100 cane toads by a pet dealer in 1957 at Miami International Airport.

Researchers don't know what year cane toads reached Southwest Florida, but the species has been breeding in the area for at least 10 years.

"There are scattered populations in Southwest Florida, here and there," said herpetologist Mike Knight, a member of the Florida Invasive Species Task Force. "It's not like they're widespread, common everywhere."

Major pest

Cane toads have also become pests in Hawaii, numerous Caribbean islands, Fiji and Australia - the cane toad is No. 16 on the Global Invasive Species Database Top 100 World's Worst Invasive Alien Species.

Also known as marine toads and giant toads, cane toads are typically 4 to 6 inches long but occasionally reach lengths of 8 inches; the native Southern toad, which is often mistaken for the cane toad, is 2 to 4 inches long.

"The problem with cane toads is their size," Lechowicz said. "They'll eat anything smaller than them."

That includes native frogs, toads, snakes, lizards, crabs, birds, small mammals and, potentially, sea turtle hatchlings.

Another concern is that cane toads secrete a toxin that can kill predators, including pets.

"They have a tendency to crawl up into dog bowls, which are like mini-ponds for them," Knight said. "Then Rover comes along, gets curious, bites the toad and gets a mouth full of poison."

Although cane toads were first documented on Sanibel in July, the species probably reached the island several years ago in mulch or plants from the east coast, Lechowicz said.

But nobody knew the new toads were on the island because they didn't breed, and, therefore, didn't make breeding calls.

"They don't like to lay eggs where there are fish because fish eat their tadpoles," Lechowicz said. "They like to lay eggs in shallow, temporary wetlands, and over the last two years, it hasn't rained much on Sanibel, so those wetlands weren't there.

"Then on July 4, we started getting a lot of rain, and the temporary wetlands filled up with water, which allowed the cane toads to breed. It's safe to say they're established in eight or nine locations."

One surprise was the discovery of thousands of cane toad tadpoles in a 5-foot by 100-foot water-filled puddle on the beach.

SCCF staff spent two days scooping tadpoles out of the puddle with nets.

"I don't know how many left before we got there," Lechowicz said. "A single female lays 35,000 eggs, and all those tadpoles could have been from one toad.

"What I'm worried about is all the places they've been breeding since July 4 that we don't know about."

Eradicating established cane toad populations is virtually impossible: Adults are only active at night and only make noise when they're breeding, so finding individual toads is very difficult, and poisoning breeding areas to kill tadpoles would kill native amphibians as well as other wildlife.

"There's a saying among people who deal with exotic species: You don't realize something's a problem until it's too late," Knight said. "You don't notice these things, and then suddenly, boom, a big, huge population makes an appearance and you say, 'Oh, we've got a problem.'"

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