National Geographic News

Mel White

for National Geographic

Published January 22, 2014

The year 2013 was an unlucky one for manatees, the gentle, rotund sea mammals that live along the coastline of the Florida peninsula. The 829 known deaths last year were the highest annual total since biologists began keeping records of this endangered species.

It's hard out there for a manatee under the best of circumstances. Because they swim just under water to feed on marine vegetation and surface regularly to breathe, they're often killed by the hulls and propellers of speeding watercraft.

Also, they're essentially tropical animals and can't tolerate prolonged periods of cold. An abnormally frigid winter in 2010 was the major factor in that year's 766 deaths, the previous record annual total.

Of the 6,500 individuals believed to live in Florida, about 300 to 450 die in an average year of old age, disease, boat strikes, and calves failing to thrive.

Two unusual factors contributed to the high mortality last year.

One was a concentration of microscopic toxic marine algae, known as a red tide, which killed 276 manatees in southwestern Florida.

These toxic algae are always present in low concentrations in the Gulf of Mexico. They are a danger to manatees during a bloom, when they become so highly concentrated in one place that they appear as a fluid red mass—a red tide, in other words.

During a bloom, fatal amounts of the algae may be attached to the plants that manatees eat. The algae may also float through the air like a powder, which manatees breathe in.

Photo of a manatee.
PHOTOGRAPH BY GEORGE KARBUS PHOTOGRAPHY, CULTURA, CORBIS
A manatee swims in murky water.

Toxins in the red-tide algae paralyze manatees so they can't breathe, and they suffocate. (Beachgoing people and dogs can also breathe in the algae, which may cause them to have itchy eyes and respiratory problems.)

More puzzling are the deaths of more than 100 manatees in the Indian River area of east-central Florida. Despite months of study and necropsies on dead manatees, scientists don't know what killed the animals.

"It started out pretty baffling, and to this point they still have no clue," says Bob Bonde, a research biologist with the U.S. Geological Survey and co-author of the book The Florida Manatee: Biology and Conservation. Though scientists speculate that a toxin of some sort is responsible, they don't know what it is or how manatees may have ingested it.

Downlisting Under Debate

This record manatee mortality comes at a time when the U.S. Fish and Wildlife Service is considering "downlisting" the species from endangered to threatened status, reflecting overall population growth during the past couple of decades. Legal protection and better public awareness have helped increase manatee numbers about fivefold, from around 1,300 in 1991.

Many environmentalists contend that the push to downlist has been driven in large part by lobbying groups such as the recreational boating industry, and by pro-development, anti-regulation politicians.

Pat Rose, executive director of the Save the Manatee Club, an influential Florida-based conservation group, believes that the high mortality rates of the past three years mean that manatees remain vulnerable and need continuing endangered status with its stricter level of protection.

"We can talk about whether the population will recover, and I certainly believe and hope so, but we can't afford too many of these records," Rose says. "Probably we're down at least net ten percent, and it could be significantly more."

Rose believes the incidence of red tide is growing, possibly because of ever-increasing runoff of nutrients such as fertilizers into marine waters.

"It's a very significant threat to manatee survival," he says. "Whether it's a long-term trend or not, in the short term it's happening more frequently and it's killing more of them."

From 2010 to 2013, about 900 more manatees died than expected—from red tides, cold weather, and other mysterious causes. "It would be absolutely wrong to move forward with downlisting without factoring in the extremely high mortality over this three-year period," says Rose.

Bonde, on the other hand, thinks that downlisting is appropriate—though only with constant monitoring—given the manatee's steady population growth. He wants to know, for example, why manatees in some areas of Florida grow bigger and more robust than those elsewhere.

"We should be precautionary about it," Bonde says. "We've done some good things. Let's make sure that we maintain the same rigors of protection that got us in these good conditions. The last thing we need is for the population to slip into an endangered state again."

Some environmental organizations have already vowed to file lawsuits if the Fish and Wildlife Service decides to downlist the Florida manatee from endangered to threatened.

Pat Rose isn't saying whether the Save the Manatee Club will take that route. But he adds that, "Being the voice for manatees, we're going to be here to speak for them."

10 comments
jodi darby
jodi darby

What a wonderful creature. I hope people will tend to be more careful as far as heading the warning signs, like the video shows. They are on the endangered list already, let's not continue to lose more of them due to people not paying attention , and harming them senselessly with their watercraft!

Stacy Dunn
Stacy Dunn

Mr. Weber:


The ONLY thing that there is too many of is......selfish, mean and ignorant human beings....yes people....Manatees...I repeat......MANATEES were here way before any human being .........get it ??!!

Pat P.
Pat P.

Love the film of the mom and calf!! Makes them so real. Besides the concern for the manatee, it shows the feelings of the community and how it impacts them as well. If the deaths are unexplained and high,they cannot be taken from the endangered list or you run the risk of loosing all you gained so far. The effort woulde be wasted....

Steven Webster
Steven Webster

There are quite a few outdated postulations here, beginning with the statement that speeding watercraft often kill manatees. While it's certainly true that some manatees are killed by fast moving boats, it's also now agreed that large vessels (barges, cruise ships, freighters) cause a disproportionate share of watercraft deaths. Since all the speed zones were put in place, manatee watercraft deaths have not been increasing, but no one knows whether the speed zones caused the reduction. Indeed, one analysis shows that the rate of decline of watercraft deaths was highest in counties with no -- repeat no -- speed zones. 

A comment below suggests sailboats only in manatee areas. In fact, as most watercraft deaths are caused by impact, not propellers, sailboats can kill, too, as manatees cannot hear their approach (and can't hear many large, slow boats, either, due to the "Lloyd's Mirror Effect", which prevents sound from preceding a large vessel's approach).

Another questionable assumption is that "protections" are responsible for the rapid increase in manatee population. A much more likely reason is that we humans have vastly expanded manatee habitat -- man-made canals, inlets, channels and, above all, power plants, which enable manatees to remain year-round in parts of Florida (and now, Georgia, Mississippi, Alabama, Louisiana and Texas) that are otherwise too cold much of the year.


The article talks about toxins being a cause of the Brevard deaths, but carcass study has ruled that out.


A current theory that needs to be examined is that there are, in some places at least, too many manatees. In Brevard, 1200 manatees are now there year-round. Before power plants heated the water -- and many are stunned to learn that power plants are REQUIRED to heat the water -- manatees migrated south during winter, giving the local seagrass beds time to recover. Now, seagrass is eaten continuously, and many believe these beds are hugely stressed, and more susceptible to devastating algae blooms.


It's complicated, granted. But, one thing seems clear. The ongoing policy that "more manatees is always better" is not a good policy. It is time to reshape our thinking to: "healthier manatees are always better."


Unfortunately, we have "protected" manatees into a state of being  utterly dependent on human management. There is a price to pay for this.

Jeri Kirkland
Jeri Kirkland

Not only the fuel & oil from boats killing the manatees, but what about the outboard motors?  In manatee territory,  maybe sailboats only?   Makes sense.

Carolyn G.
Carolyn G.

Obviously, the Manatee is still endangered! The numbers have decreased 10 percent in three years, that means they would be extinct in 27 years!!!! We have to protect them!!! Common sense applies here!! iIf only everyone had some !!!

m s
m s

So I can't but help point this out. We had a major oil spill in the gulf, it went everywhere, currents taking that out into the ocean. The companies who spilled the oil order a contraversial chemical to breakup the oil so it's easier to clean which causes terminal cancer in even the most well covered well protected humans. It disperses into the local oceans as well, then immediately after we start seeing mass die offs of multiple mammals, of which are reported the most are the dolphins off the east and gulf coasts, and now the manatees. Uhm when are scientists going to connect 2 + 2 and realize it was the oil and the chemical that poisoned these creatures. Am I the only one seeing this?

Owen Busse
Owen Busse

Save them! They don't deserve to die!

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