UF study gives new insight into manatees


Published: Saturday, June 22, 2013 at 5:23 p.m.
Last Modified: Saturday, June 22, 2013 at 5:23 p.m.

Five thousand of Florida's most beloved inhabitants are still something of a mystery.

But manatees are closer to being understood from the inside out, with a recently published University of Florida study that reveals how the sea cow's heart functions.

The study, published in the June issue of the Journal of Zoo and Wildlife Medicine, describes the results of 14 Florida manatees who underwent echocardiography. The goal was to develop parameters of normal heart function for animals of various sizes and ages.

"This gives us another diagnostic tool to determine what makes a manatee tick," said Dr. Bob Bonde, a biologist with the U.S. Geological Service in Gainesville who helped capture the manatees for the study.

"We know they're marathoners and can travel long distances," Bonde continued. "They have a big heart, and it's there for a reason."

But until now, scientists have mostly studied manatees' hearts post-mortem, unveiling certain heart conditions — some of which are associated with cold stress syndrome, a common cause of manatee death.

A previous study looked at heart chamber size, heart rate and rhythm, but the UF study is the first to look at heart function in live manatees.

Trevor Gerlach, an intern in UF's aquatic animal health program who worked on the study, compared manatees undergoing echocardiography, especially as they age, to someone's grandmother undergoing a complete physical exam. Yet the physical challenges of getting manatees to the exam table are considerably larger.

Adult manatees weigh an average of 1,500-1,800 pounds, and the longest they are out of water is only a few hours — and that's if they've been injured and need to be transported, Gerlach said.

The mammals that Gerlach and his colleagues studied were allowed out of the water for just an hour — from capture to release — but the mammals also were being tested in other studies at the Marine Mammal Pathobiology Lab in St. Petersburg.

So 10 minutes is all that Gerlach and his team had to give each manatee an echocardiography, during which time the animals were rolled onto a large table, belly down.

Based on the snapshot of manatees' hearts, an adult heart is about the size of a basketball and is proportional to its body size, Gerlach said.

While manatees have four ventricles like other mammals, they also have a gap between two ventricles that distinguishes them from other species, Gerlach continued.

"We don't have any reason to think it makes them better off. It's just something that's unique to them," Gerlach said.

The researchers found that some manatees had enlarged chambers, which in other mammals such as dogs and humans "would indicate some degree of cardiac dysfunction," Gerlach said.

They also found some evidence of valvular regurgitation, a condition in which blood flows backwards, which in extreme cases may lead to conditions like congestive heart failure, Gerlach addded.

But mostly, the published study and another ongoing study that looks at 50 additional manatees are establishing the parameters for healthy manatee hearts so scientists know what to look for.

"It's an endangered animal, and there's a ton of money that goes into conservation of animals," Gerlach said. "To figure out where research money is best spent, we need to understand its biology and physiology more."

Manatees typically live well into their 30s, although the oldest known manatee, "Snooty," is 63 years old and lives at the South Florida Museum in Bradenton.

Prevalent causes of death include cold stress syndrome and watercraft entanglements, but "natural causes" is also a large category that remains largely undefined.

If heart disease is one of those causes, scientists might now be able to monitor and even prevent it because now the echocardiography provides them with some baseline measurements, Bonde said.

"Now we can look more specifically at things that might impact their lives, and that could be through diet, nutrition, reproduction, genetics. All those things are questions that we can ask in the future," Bonde continued, adding that one question might be whether inbreeding causes heart dysfunction. Another issue would be mitigating stressful environments for manatees.

"These poor animals aren't really telling us their woes and problems," Bonde said. "The better we can prepare ourselves to be able to tell what's going on, the better we can cohabitate with them on the planet."

Contact Kristine Crane at 338-3119 or kristine.crane@gvillesun.com.

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