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Cold has hit manatee population last two years

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Published:   |   Updated: March 19, 2013 at 10:41 AM
TAMPA -

Sometimes there is nothing you can do to protect one of nature's gentlest creatures from the cruelties of Mother Nature.

At one time, the main danger to sea cows bobbing in Florida's waters was inattentive speed boaters who plowed through manatee-rich areas, bows crunching shoulders, propellers gouging backs.

That could be dealt with, if not eliminated. Strict laws were enacted, manatee sanctuaries have been established and educational programs are available to teach boaters about when and where manatees gather along Florida's coastline. Fatal vessel encounters dipped.

Over the past few years, though, boating-related deaths of Florida's officially adopted marine mammal have been eclipsed by the cold.

The number of manatees dying of cold is a troubling trend for state wildlife officials, who say that for the third year in a row, frigid waters have has claimed a higher-than-usual number of manatees.

"Basically, we've had a run of very cold winters," said Carol Knox, a biologist with the Florida Fish and Wildlife Conservation Commission. "It's one of those cyclic things that just occur, just one of those things that happens."

Of the 453 manatee deaths recorded in 2011, 112 were attributed to the cold, according to figures recently released by the commission. The year before was even worse; 282 of 766 deaths were cold-related.

That was the year when much of the state shivered under 11 straight days of subfreezing temperatures. The cold snap took its toll on flora and fauna and even resulted in fish kills around the Tampa Bay area.

There's not much that humans can do to keep manatees warm, Knox said, except to make sure the access routes to warm spring-fed rivers and estuaries are clear of obstruction and that the flow of spring water remains stable.

Sometimes, Knox said, survival is left to the vagaries of nature.

Typically, the state gets its first taste of cold winter weather in November and December, and manatees take note.

"They key off air temperatures and water temperatures," Knox said. "When the first cold front comes through, one that is significant enough to get the temperatures down, that gets them on the move. They are moving toward warmer water."

If there are no early cold snaps, manatees may still be in open water and unprotected when sudden freezing temperatures hit, she said.

"It all depends on how the cold weather stacks up and how it emerges each winter," she said. "If manatees are already in their warm-water sites, they are fine. Groups that are in warm-water sites sustain very few cold-stressed deaths."

The population of Florida's manatees has blossomed over the past 30 years. At the end of January 2011, officials counted nearly 5,000 manatees in the waters around the state.

"We're hopeful that we have enough animals out there to make the population more resilient to these threats," Knox said.

The 282 cold-related manatee deaths in 2010 was a record and biologists coined a new term: cold-shock death. That's when manatees in warm water are forced to go out to forage for food during extended cold spells.

They hit the cold, open water and the sudden change in temperature actually shocks them to death. It was a relatively new phenomenon, biologists say.

In 2009, the commission recorded 56 manatees dying from the cold, out of a total 429. In the previous five years, cold stress accounted for an average of 30 manatee deaths a year, wildlife officers said, and over the past two years, an average of 86 manatees died in boating collisions.

The total number of reported manatee deaths in 2011 was the second-highest on record, after 2010. The number of deaths in 2009 was the third-highest.

"We are concerned about the number of manatee deaths the past three years, including those resulting from exposure to cold weather," Gil McRae, director of the commission's Fish and Wildlife Research Institute, said in a news release.

"Over the next few years, we will use data from monitoring programs to better understand any long-term implications for the population," he said. "We will continue to work with our partners to enhance the availability of natural warm-water sites, which are important habitats for the species' survival."

Save the Manatee Club Director of Science and Conservation Katie Tripp said that manatees already in warm-water areas when freezes hit fare far better than those caught off guard by a sudden cold snap.

She said the three-year trend is troubling. Enough manatee deaths on any given year, she said, "and you have the potential for a population level impact."

She said it is important to maintain warm-water coastal springs, the flow of which tends to diminish with nearby groundwater pumping for human consumption.

"When there is more groundwater withdrawal," she said, "there is less water in the springs that the manatees depend on. And that puts them more at risk."


kmorelli@tampatrib.com (813) 259-7760

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