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Computer model predicts change in fortunes for once-endangered manatee

Florida's manatee population is likely to double to 12,000 over the next 50 years, according to a controversial computer model — a sharp departure from the days when biologists feared manatees might go the way of the dodo.

The latest forecast, released Tuesday, comes from a U.S. Geological Survey computer model that led the federal government last month to take manatees off the endangered list and instead classify them as threatened.

But that model has been wrong before, environmentalists warn, and the latest version's flaws will likely play a crucial part in any federal lawsuit to overturn the government's decision.

Save the Manatee Club president Pat Rose said the computer model is not grounded in reality.

"I don't think it captures what is happening or what is likely to happen in Florida," Rose said, noting that it does not take into account the effects of climate change and other factors.

Even the model says the manatees' future is not entirely rosy. It anticipates that more manatees will be killed by boats than ever before, and more will be killed by Red Tide algae blooms, according to model designer Michael Runge.

It also predicts waterfront development will drive a major shift in where manatees live and drive them away, especially from the Tampa Bay area.

The manatee population is likely to plunge in the two areas where the majority of them now live, he said. One of those locations is the bay area, home to hundreds of manatees, especially in winter. They will lose habitat here, and thus lose the sea grass they need for food.

Instead of just dying off, though, the model predicts Florida's manatee population will shift northward, pushing into areas in North Florida where manatees are now rarely spotted, and increasing the number that call Crystal River home year-round.

"How are all those animals going to survive the winter?" asked Rose, a critic of both the computer model's results and the federal agency's decision to change the manatees' status.

Manatees are extremely sensitive to cold. In winter they seek refuge in the warmth of Florida's springs and power plant outfalls. But springs across the state have been losing their flow to overpumping of the aquifer, and older power plants are expected to shut down as new technology makes them obsolete.

Runge acknowledged that those factors could alter the manatees' future population.

Rose said he respects Runge's work, but questioned the notion of making a decision about the manatees' status based on what has been an evolving model.

For instance, a 2007 version of Runge's model said Florida had room for no more than 5,000 manatees. The most recent aerial survey found more than 6,000. So seeing the new version predict the population could double from 6,000 to 12,000 "was a surprise," Runge said. A larger population will survive more adversity.

"If the population can grow to 10,000 or more," he said, "then you can hit it with a lot of threats."

Federal officials said the model shows manatees are no longer teetering on the brink of extinction, and thus no longer fit the definition of an endangered species. The Save the Manatee Club strongly disagreed with that analysis.

Rose and other advocates opposed to the change pointed to the fact that more manatees were killed by boats last year than ever before. For the first time since officials started keeping track, the number of manatees killed by boats topped 100.

Runge said the model showed the number of manatees killed by boats will continue to rise. But as long as it stays in the same proportion to the overall death rate that it is now — about 25 percent a year — then it shouldn't affect their future viability, he said.

But if boat deaths grow beyond that 25 percent proportion, Runge said, the future of the species will once again be in doubt. The report on the modeling stated: "If the rate of watercraft-related mortality were to double, the risk of quasi-extinction would increase more than ten fold."

The latest model also predicted one other rising threat: A lot more manatees will be killed by an increase in Red Tide algae blooms in the future. Red Tide "will be more frequent and more severe" over the next 40 years, Runge said.

Manatees had been classified as endangered ever since the first endangered species list came out in 1967. They weren't put on the list because of the size of their population. Their habit of remaining submerged for five minutes at a time makes them difficult to count.

Instead, records show, they were put on the endangered list because of the threats they faced from being clobbered by boats and from losing habitat to waterfront development. During last month's announcement of the change in status, federal wildlife officials said that despite the rise in boat-related deaths, those threats were no longer as dire as they once were.

The computer model Runge came up with is based in large part on the research done by biologists at the Florida Fish and Wildlife Research Institute in St. Petersburg.

Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.

The model

For a link to the U.S. Geological Survey's latest version of the manatee computer model results, visit: https://pubs.er.usgs.gov/publication/sir20175030.

Computer model predicts change in fortunes for once-endangered manatee 04/11/17 [Last modified: Wednesday, April 12, 2017 11:10am]
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