Wednesday, 21 September 2011

Coquis Frog May be Leveling off in Hawaii

Unless you sleep in a soundproof chamber, you've probably already heard the news: The great Hawaii Island battle between man and coqui is over. The little, quarter-sized frogs have won.

But, researchers said this week, even as the Puerto Rican invaders continue to spread to new areas of the island, their population numbers are leveling off and even dipping back down slightly in areas where they have thrived.

On Thursday, coqui experts with the University of Hawaii and the state Department of Agriculture said state spending has ended for some projects aimed at population tracking and eradication efforts. The focus, they said, has shifted to keeping the coquis on island, and preventing their spread to the other Hawaiian islands and primary shipping destinations, like California.

"There just isn't much new to go on," said William Mautz, professor and chairman of the University of Hawaii at Hilo's Biology Department. "Much of the funding for working on coqui frogs has dried up, now that they've proven difficult to remove. They have continued to spread to parts of the island
that are wet, and they will continue to do so."

Mautz said Thursday that most likely the coqui's spread on the Big Island would primarily be dictated by altitude.

"They'll probably be limited to somewhere around 5,000 feet," he said.

"They're already up that high now in Volcano. It's not clear how much higher they might go."

While several different techniques have been identified to kill coqui frogs, nothing is perfect, Mautz added. Sprays containing baking soda or citric acid have been proven to be effective, he said, but they must make direct contact with the frogs in high enough concentrations to work. And in some environments, there are simply too many hiding places for the frogs.

"In some parts of the island, it's easier to control them (the coquis) than in others," he said. "In areas with lots of a'a lava, like Puna, they're very difficult to control. All the cracks, and channels and tunnels beneath the lava, where they can get underground and hide, those areas are the areas with the most dense populations. In areas with older soils, where they can't get underground, you have fewer, such as in the Kohala mountains."

As some populations of coqui frogs have settled in to their new habitats on the island, members of the public have reported spotting what they consider to be unusually large specimens of the frogs. But, Mautz said, that is just a result of the population becoming established.

"It's not true that the frogs are getting larger. What's going on is that the populations of the frogs are maturing, so there are more and more frogs that are living longer. They don't stop growing until 6 or 7 years old, so there are more large, adult frogs showing up with more frequency," he said.

The larger adult frogs may also explain why researchers have seen population numbers dip in some areas that have been overrun by the little chirpers.

"In many places, they appear to be not as dense as they were," Mautz said.

"Don't get me wrong. There's still plenty of them. But they have dipped a bit. It's a typical pattern for an invasive species. When they first become established, their population shows a spike."

Later, as the population reaches an equilibrium with its environment, the population growth hits a plateau. And, he said, larger adult coquis also tend to be cannibalistic.

"They'll eat younger, smaller frogs," he said. "They'll eat just about anything that's smaller than them."

While Mautz did not have recent population number counts, as funding for that program was discontinued a few years ago, he was able to say anecdotally that he and other experts had noted a drop in the population of coquis at Lava Tree State Monument, the area on the island with the highest
concentration of coquis.

"The frogs just don't appear to be as loud as they were six or seven years ago," he said.

Arnold Hara, an entomologist and extension specialist with the UH College of Tropical Agriculture and Human Resources, formerly worked with the project aimed at keeping track of coqui populations. But, he said after funding dried up, he moved on to direct containment efforts in the export of potted plants.

"My focus is now on treatments to prevent them from spreading to other islands and California," Hara said. "There's been interception of these frogs in California. They've had outbreaks in Disneyland and Hermosa Beach, among other areas.

"We admit that the Big Island is fairly well-infested and eradication is pretty much impossible. So, we're focusing on preventing the spread."

Using a Matson shipping container modified with shower nozzles, he gives plants that are to be shipped off island a hot shower. The temperature, he said, kills stowaway coquis and their eggs. According to Hara's most recent numbers, a total of 30,000 potted foliage plants were treated in the chamber during the month of June.

In addition to state funds no longer going toward coqui control, Hawaii County ceased its own coqui spraying program in April 2010, and in an unpopular move, attempted to auction off its 26 sprayers that it had been loaning out to different community groups following through with their own
control efforts. Public outcry led the county to cancel the auction and transfer the oversight of the equipment from the Mayor's Office to the Department of Research and Development's agriculture office.

from: HAWAII TRIBUNE-HERALD (Hilo) 21 August 11 (Colin M. Stewart)

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