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Manatee deaths prompt federal investigation

Fatalities far outpace typical winter rate

Mary Helen Moore

Daytona Beach News-Journal USA TODAY NETWORK

The U.S. Fish and Wildlife Service announced Tuesday the recent spate of manatee deaths in the Indian River Lagoon would be declared an unusual mortality event, channeling muchneeded federal resources into an investigation of what's causing the die-off.

Manatees have been dying at an alarming rate in recent months, with the Florida Fish and Wildlife Commission tallying 416 deaths in January and February. Florida has averaged 578 annual manatee deaths in the past five years.

That's more than seven deaths a day, far outpacing the typical rate for the winter months.

More than 60% of the 2021 deaths — 4.5 deaths per day— have occurred in counties on the Indian River Lagoon, the 156-mile-long estuary that stretches from Ponce de Leon Inlet in Volusia County to Jupiter Inlet in Palm Beach County.

Pat Rose, executive director of Save the Manatee Club, said as of Monday, the non-profit had documented 539 deaths and 80 rescues statewide in 2021.


A manatee feeds on the vegetation at Blue Spring State Park in Orange City on Sept. 4, 2020.


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Rose expects the 2013 record of 830 manatee deaths in Florida to fall before 2021 ends.

“Sadly I think we will surpass it,” Rose said. “The ramifications are quite severe, not just for manatees but for the whole Indian River Lagoon system.”

This week's declaration was prompted by a March 8 letter from U.S. Rep. Stephanie Murphy (D-Winter Park) and a request from FWC.

“Florida's diverse animal life is deeply important to people in our state, and few creatures are more beloved than the manatee,” Murphy said in a news release. “I'm pleased that, in response to my request, the federal government has determined the spike in manatee deaths requires a swift and decisive response.”

The National Oceanic and Atmospheric Administration and USFWS will now partner with FWC and non-profit organizations in an attempt to minimize deaths, determine the event's cause and the role of environmental factors, and find out the effect on the manatee population.

Rose said he hopes more federal (and state) dollars will reach the area in time to prevent the situation from worsening.

“To use a technical term, it was a nobrainer,” Rose said of the decision to declare an unusual mortality event. “Hopefully it's going to be improving, but that all needs to be documented more carefully. And there's still manatees needing to be rescued. That's got to be the first and foremost.”

Seagrass is quickly vanishing

Though the cause of the die-off is not yet determined, researchers speculate starvation could be to blame for many of the deaths in the Indian River Lagoon system.

Florida manatees are a threatened subspecies of the West Indian manatee that can reach 1,200 pounds. Packing on that much weight requires an enormous amount of food, and manatees spend most of their time feeding or resting. Manatees are herbivores and get much of their nutrients from munching on seagrass beds.

But since 2009, 58% of the seagrass in the lagoon system has disappeared, choked off from sunlight because of poor water quality, according to the St. Johns River Water Management District.

“Initial assessments indicate the high number of emaciated manatees is likely due to a decline in food availability. Seagrass and macro algae coverage in this region and specifically in the Indian River Lagoon has declined significantly,” FWC wrote on a website dedicated to the investigation.

Seagrass does far more than serve as a food source for manatees. The seven varieties found in the lagoon plays a critical role in its ecology, supplying oxygen to the water, anchoring sediment in place, and providing a habitat for fish, shrimp, and other creatures.

What can be done?

Solutions exist, and have led to the restoration of tens of thousands of acres of seagrass beds in Tampa Bay since the 1970s.

That recovery took decades of nutrient reduction from all of the counties in the Tampa Bay watershed, said Jim Fourqurean, director of the Coastlines and Oceans Division of the Institute of Environment at Florida International University.

“It doesn't take us long to make the water quality inappropriate. It took 40 years for the Tampa Bay to recover,” Fourqurean said.

Planting seagrass is difficult and expensive and won't work unless water quality in the Indian River Lagoon improves.

Fourqurean put it simply: “Seagrass tends to grow in places where seagrasses can grow.”

Plants rooted underwater are extremely sensitive to changes in water quality because they need a lot of light to penetrate the water column, according to Fourqurean, who researches seagrass ecosystems in his Miami-based lab.

When pollutants like nitrogen and phosphorous accumulate, they fuel algal blooms that prevent light from reaching seagrasses even in shallow water bodies like the Indian River Lagoon.

Then loss begets loss, as the seagrasses that once held sediment into place die off and dirt particles further cloud the water.

Rose said solutions must both clean up the water and prevent large amounts of nutrients from entering the lagoon.

“There's a huge amount of work to be done,” he said. “This will take many, many years if you do everything right. And if you do everything wrong, there will be many more deaths.”

Algae, cold prolific manatee killers

When aerial surveys began in 1991, there were an estimated 1,267 manatees in Florida, according to the USFWS. Today's population estimates in Florida are somewhere around 6,300, a recovery that prompted the USFWS to upgrade Florida manatees from endangered to threatened in 2017.

This is the first marine mammal unusual mortality event NOAA has declared since 2019 and the second open investigation into manatee deaths in the Indian River Lagoon.

The other open investigation is into the 2013 die-off of 111 manatees in the lagoon for reasons that are not yet fully understood.

Rose said in 2013 heavy rains brought excess nutrients into the Indian River Lagoon, leading to a harmful algae bloom of Gracilaria that poisoned manatees and dolphins alike.

“Much of the root cause is the same,” Rose said There have been 71 declarations of marine mammal unusual mortality events since 1991, according to NOAA, but the declaration doesn't guarantee answers. About 45% of the closed investigations wound up with an undetermined cause.

Florida manatees have now been the subject of 10 of those investigations, making them one of the most frequently involved species alongside bottlenose dolphins and California sea lions.

Of the closed cases, six were caused by biotoxins released during harmful algae blooms of red tide in the Gulf of Mexico.

Red tide is caused by the toxic algae Karenia brevis, which releases a potent neurotoxin known to kill fish, turtles, seabirds, and marine mammals. It is dangerous for humans to breath and make shellfish poisonous to eat. Those blooms can also occur along the Atlantic coast, but it is far rarer.

Two were attributed to unusually cold weather, which manatees are exceptionally vulnerable to.

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