USDA eyes poisoning iguanas; cost of lizard program going up again

Rat poison to kill the island’s iguanas? That’s what the United States Department of Agriculture says it’s considering using in its campaign to eradicate the lizards. Also, USDA officials said Friday, Nov. 20 that the cost of the program will increase by $30,000 next year.

Dr. Michael Avery, wildlife biologist with the USDA, told a crowd of more than 30 gathered in the Woman’s Club Room at the Boca Grande Community Center, that the agency has been conducting studies to determine what poisons would best kill the lizards. He said zinc phosphide was a product they determined would work.

One problem. It’s also lethal to mammals, birds and fish.

“We’re trying to develop bait and toxicant, because shooting and trapping are very useful but may not be able to do the whole job,” Avery said.

“We started with acetaminophen (otherwise known as Tylenol) as an oral toxicant and inserted it into maraschino cherries, but we weren’t totally successful in getting the animals to succumb. Zinc phosphide has proven to be very effective, as we’ve had virtually a complete mortality rate with just a very small amount.”

Avery said that zinc phosphide is activated when it comes in contact with the liquid in the iguana’s stomach, which turns it into phosphine gas. It is a common ingredient in rat poison.

“We think we have a good approach we can use, and have created an artificial bait that the animals will take and will be more usable in the field than cherries,” Avery said. “We’re still working on non-target animal hazard assessments, and it will require field trials to determine how other species respond to the bait that we have made.”

When asked by audience members how the poison affects other animals and people, Avery admitted it is very lethal to all.

“It is a toxicant that has a very broad spectrum … it’s bad for everything,” he said. “You have to be very careful of your formulation and your presentation. It’s why we go through several steps so we can send data to the EPA to satisfy their requirements.”

One audience member, former iguana trapper George Cera, asked Avery why they would use such a highly-lethal poison in an area that is a wildlife sanctuary, and also a place where many people walk their pets.

“The idea of throwing something around the island when people have pets, it doesn’t make any sense,” he said. “How can you guarantee other animals won’t eat this bait, and what happens to animals that would eat an iguana that has been poisoned by this stuff?”

Avery said that in a normal household dosage of rat poison, the ratio of zinc phosphide to other inert ingredients is two percent. USDA studies are based on 25 mg. concentrations, which, he said, is approximately half a percent.

“The amount we would be using is four times less on a percentage basis by weight of the bait itself,” Avery said. “And we wouldn’t just be throwing it on the ground, we would be presenting the bait in a way that exposes only the iguanas to it.”

Avery admitted they hadn’t figured out how to do that yet, and that even in the small amount he described using for iguanas, it could still be lethal to other animals and humans.

The island’s iguana tax board also passed a motion to accept the USDA contract for another year. The cost of the program will climb from $70,000 to $103,000.

“This is a recommendation made by the panel to the Lee County commissioners, a recommendation only,” Walker said. “This advisory committee doesn’t make decisions. The commissioners will decide whether they want to take our recommendation or not.”

Walker explained that the reason for the increase was due to the fact there was a limited amount of money in the program’s coffers last year because of additional money owed to Cera.

Avery, who is head of the department in Gainesville that researches all iguanas brought from the island, gave a report to the board, saying they have watched the lizards decrease in size from the time they started the program. The USDA started eradicating iguanas in Charlotte County in 2008, and in Lee County in 2009.

“There has been a length and mass decrease in both males and females since we started,” he said. “In Charlotte County we have seen a decrease in length of 33 percent. When we look at body mass, we see a 63 percent reduction from year one to year two. Lee County numbers look a lot like Charlotte County’s. We’re also seeing a 71 percent reduction in the size of the male iguanas’ testes, which reflects the size of the animal and its capacity to hold territories and monopolize females.”

What that means in layman’s terms is that because the number of larger iguanas has already been eradicated, the population has been reduced to smaller, less mature animals. Smaller animals produce fewer eggs in each clutch, which means there are fewer iguanas on the island.

Avery said in Charlotte County they have eradicated 1,900 iguanas during 2008 and 2009. In Lee County for 2009, they have killed 1,600.

In the first two years of the Lee County program, trapper Cera eradicated approximately 12,000 iguanas.

Libby Walker, Lee County’s director of public resources, asked another USDA employee, Bernice Constantine, whether he thought another year of trapping by that agency might bring a “maintenance” plan into play.

“Would it be fair to say that if we went forward with another year of working with the USDA, we could formulate a maintenance plan and figure out where we’re going in the next four or five years?” she asked.

“We need to take it one year at a time,” Constantine said. “That’s why Dr. Avery is doing the work he’s doing, keeping track of our success and, at some point, with the information from him, we can look at it. We should have some consistent data in a year or two.”

Cera was quick to respond.

“I think you can see by the numbers that you are already in the maintenance part of the program,” he said. “I don’t understand why the price has gone up, when you’re catching a lot less iguanas now.”

The board’s chairman, Ron Gutman, said that he believed the meeting gave the board a good idea of where the program is headed.

“Most people say we’re making good progress and that people are, by in large, pleased,” he said.

Charlotte County residents who have iguanas on their property that they would like to report to the USDA can call Mike Kennedy at (352) 284-5740. Lee County residents can contact Norm Schoch at (352) 258-9797.