Boats top cause of Florida manatee deaths in 2019

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As more sea cows and captains crossed paths on Florida‘s waters, boats became the leading cause of manatee deaths this year and are on course to top last year’s record 124 manatee deaths by boat, according to early state statistics.

Through Nov. 15, Florida had 119 manatee deaths by boat, topping the five-year average of 89 boat-related manatee deaths through that same point of the year, data from the Florida Fish and Wildlife Conservation Commission show. 

Last year, natural causes were the leading cause of death, claiming 230 manatees, 79 of them in Lee County, FWC statistics show.

Here is FWC’s manatee mortality data for 2019, through Nov. 15, the most recent available. Drag your mouse over the bar graph to see how many manatees died from each cause.

Overall, sea cows fared better through mid November this year than in the last few years, with 455 dying from all causes by Nov. 15, compared to 751 manatee deaths by that date in 2018 and 482 manatee deaths by that date in 2017.

A record 830 manatees died in 2013, including 158 of 244 manatees deaths that year in Brevard from undetermined causes. Biologists suspect many of those 158 manatees may have fallen victim to a seagrass die-off that disrupted the makeup of healthy bacteria in their digestive tract, leading to the disease.

The second most on record — 824 manatees — died last year.

Boating advocates who fight against manatee go-slow zones have long pointed out that manatee deaths are going up mostly because the species’ population growth. Brevard and Lee counties, in particular, tend to have the most manatee deaths from all causes because they have large manatee populations lured there by vast seagrass habitats.

This year’s been no exception. Lee County’s 24 boat-related manatee deaths were the most in Florida, followed by Brevard’s 13 watercraft-related deaths. Volusia ranks third with 12 watercraft-related manatee deaths.

Florida‘s annual manatee counts have more than doubled in the past 20 years, to a record 6,620 animals in 2017, according to statewide yearly aerial and ground counts. As a result, the federal government reclassified the manatee from an endangered to a threatened species, a less serious designation under the federal Endangered Species Act. 

Florida wildlife officials counted 5,733 manatees this year during its annual winter survey, Jan. 28 to Feb. 2. But biologists consider the statewide annual surveys only a minimum count of the manatee population, so there could be thousands more sea cows.

Meanwhile, registered vessels have increased as well, although they yet to recover to more than 1 million vessels in Florida from before the 2008 economic crash.

Brevard, Lee and Collier counties tend to top the list of manatee deaths for all causes of manatee deaths, including boats, because the amount of seagrass habitat in those counties attracts so many sea cows, as well as fishermen with boats.

Seagrass in the Indian River Lagoon — ailing in recent years under an onslaught of harmful algae blooms — has shown recent signs of improvement, especially in the estuary’s southern reaches.

But longer-term seagrass declines continue to tax how many manatees the lagoon and other coastal waters can support into the future, some biologist have warned. 

Citizens for Florida Waterways, a boating advocacy group in Brevard, has also warned for years that manatees may be beyond ecological carrying capacity in the lagoon.

Manatee herds in some areas of the lagoon have been known to graze on and disturb up to 40 percent of the seagrass beds, research shows, removing 80 to 96 percent of the seagrass and 50 to 67 percent of the roots, one study showed.

One 1991 study in the northern Banana River by an environmental consultant to NASA found manatees significantly reduced seagrass within just six weeks.

Because of NASA’s Kennedy Space Center, the north Banana River has been closed to boating since 1963, making it a manatee mecca where sea cow numbers had ballooned to more than 1,200 manatees by 2014. But several severe algae blooms in the past six years killed off a majority of the seagrass manatees rely upon in the Banana River.

Manatees grow increasing vulnerable during winter months. Hundreds of manatees gather flipper-to-flipper each winter at the two lagoon-side power plants in Port St. John and other power plants in Florida, keeping them farther north than they’d otherwise be. Before power plants, manatees seldom migrated farther north than Sebastian Inlet on the east coast and Charlotte Harbor on the west coast, biologists say. That puts them in areas with scant seagrass during cooler months.

When water temperatures stay below 68 degrees Fahrenheit for weeks at a time, manatees suffer cold-stress syndrome. That causes weight loss, fat loss, dehydration and other health problems that can kill them weeks later.

This year’s winter killed 44 manatees statewide from cold stress, compared to 78 last year, and a five-year average of 32 cold-stress manatee deaths.

Here’s how Florida‘s 2019 manatee deaths (through Nov. 15) break down:

  • Watercraft — 119 
  • Flood Gate/ Canal Lock — 3
  • Other Human — 5
  • Perinatal — 65
  • Cold Stress — 44
  • Natural — 60
  • Undetermined — 99
  • Unrecovered —60
  • Total — 455

Source: FWC

Jim Waymer is environment reporter at FLORIDA TODAY.

Contact Waymer at 321-242-3663                                         

or jwaymer@floridatoday.com.

Twitter: @JWayEnviro

Facebook: www.facebook.com/jim.waymer

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