Manatees in the Indian River Lagoon and elsewhere along the coast have been dying at such alarming rates that the federal government has launched an investigation, and directed additional money and personnel to rescue the animals and determine what is causing the spike in deaths.

NOAA Fisheries and the U.S. Fish & Wildlife Service last month declared an “unusual mortality event” for Florida manatees after at least 539 died between Jan. 1 and March 19, including 235 of them in the Indian River Lagoon or its tributaries.

That amounts to nearly 10 percent of the estimated statewide manatee population of 5,733, according to Save the Manatee, a nonprofit conservation organization, and is almost as many as died in the entire previous year. Eighteen manatees have been found dead along Indian River County’s shores.

The new UME was declared just three years after the marine mammals were taken off the endangered species list and re-categorized as merely “threatened” under the U.S. Endangered Species Act. The UME designates the Florida Fish & Wildlife Conservation Commission to lead the response to the crisis, and provides additional funds and staff support to the agency and its environmental partner groups.

The deaths have come in such an onslaught that state wildlife rescuers can’t keep up; there have been no necropsies performed on 372 of the animals, some of which were too decomposed to examine by the time they were seen by state investigators.

As for the others, veterinarians so far have determined that cold stress killed 27; 66 died of natural causes; and 20 were struck by boats. Others appear to have died from starvation, and many scientists believe the drastic decline of seagrass in the Indian River Lagoon over the past decade is the prime culprit in the crisis – that the lack of food has caused many of the threatened sea cows to starve to death.

Seagrass and other aquatic vegetation is the manatees’ preferred diet, and they eat a great deal of it. During cool winter months when ocean water temperatures fall, manatees flock to warm-water refuges, such as the lagoon and inland freshwater springs, to graze on seagrass and other plants.

But today, according to the St. Johns River Water Management District, the Indian River Lagoon has only about 42 percent of the seagrass it had a decade ago, leaving much of the lagoon bottom barren.

“Environmental conditions in portions of the Indian River Lagoon remain a concern,” according to the state fish and wildlife agency’s manatee mortality website. “Preliminary information indicates that a reduction of food availability is a contributing factor.”

Save the Manatee says the federal government itself bears much of the blame for the surge in manatee deaths. “Staffing for the manatee recovery program has been reduced, despite the growing problems manatees have faced since they were prematurely and unjustifiably downlisted from ‘endangered’ to ‘threatened’ in 2017,” a statement on the organization’s website says.

“The federally managed Manatee Recovery Program was once the pride of the FWS. Now it is underfunded and neglected ... There is no active Manatee Recovery Team, Manatee Implementation Team, or Manatee Warm-Water Task Force.”

To the extent starvation from lack of seagrass is driving the increase in deaths, then at least one veteran marine scientist who studies the lagoon says the situation is not going to get better next winter – or anytime soon. 

Dr. Dennis Hanisak, research professor at Harbor Branch Oceanographic Institute and organizer of the school’s annual lagoon symposium, traces the demise of seagrass in the 156-mile-long estuary to the extended cold snap in early 2010, followed by the algae “superbloom” in 2011, followed by the massive fish kills of 2016; then the passage of Hurricane Irma in 2017; and most recently another algae bloom of undetermined origin that caused a fish kill last fall in the northern lagoon.

“It’s not gone. It’s having a winter break,” Hanisak said of the most recent bloom. “It’s probably going to continue.”

Algae blooms kill seagrass by preventing sunlight from reaching it. The dead seagrass then robs the water of oxygen, suffocating fish and depriving other marine animals such as manatees of their food supply. What causes the algae blooms, Hanisak says, is an overload of the nutrients nitrogen and phosphorus from “septic tanks, bad use of fertilizer from lawns and agriculture.”

“We’ve totally disrupted the system with too much nutrients,” he said. “Everybody kind of contributes to the problem.  The only thing to do is try to reduce nutrients going into the lagoon.”

That effort is underway on multiple fronts, but Hanisak says improvement in water quality and habitat won’t happen right away.

“It will take several years before you see improvements in water quality and a few years after that, an improvement in seagrass,” Hanisak said.

“It’s going to take a fairly long time to turn it around.  I wonder why it took this long for this [manatee] starvation thing. 

These seagrasses haven’t been good for a long time. Nobody really saw it coming. What’s going to happen going forward for the manatees is up in the air.”