One in four manatees found dead in Florida this year died within one year of birth, state data shows, making it the leading known category of death for sea cows so far in 2024.
The 66 so-called "perinatal" deaths also are almost double last year's and the five-year average of 35 manatee deaths within a year of birth, as well as this year's 34 deaths by collisions with boats.
But state biologists aren't sure yet what so many young manatees dying might mean. That's also obscured by how many aren't even examined — 98 so far this year — because they're too decomposed, not recovered or for other reasons.
What's happening?
This year's jump in perinatal deaths — although the scientific jury is still out — could be fallout from two years of manatee famine in the Indian River Lagoon region due to seagrass loss. Biologists at the Florida Fish and Wildlife Conservation Commission (FWC) had warned of long-lasting health effects of malnutrition on the next generation of manatees. But it also could be a sign that manatee reproduction is slowly getting back to usual, after years of fewer births during the famine.
What do state biologists say?
More mating may be leading to more births but also more deaths due to malnourished mothers, which biologists warn could have long-term impacts on reproductive success.
From the carcasses they've been gathering since last year and field observations, state biologists had expected an increase in the number of small dead and stillborn calves this year, Martine deWit, lead veterinarian at FWC's marine mammal pathobiology lab in St. Petersburg, said via email.
What is an Unusual Mortality Event?
The manatee death toll got so bad in late 2020 that in April 2021, the National Oceanic and Atmospheric Administration declared the die-off an Unusual Mortality Event (UME). The declaration focuses federal efforts and funding to study and mitigate the die-offs. The UME is ongoing.
Can you feed manatees?
No. It's illegal to feed manatees in the wild. But because most manatees in 2021 were dying of starvation, in a first-of-its kind pilot project, state and federal biologists fed manatees lettuce at the warm-water discharge area of the Florida Power and Light power plant in north Brevard during two consecutive winters. FWC now says enough seagrass has grown back that feeding them there again next winter is unnecessary.
How well did manatees reproduce in the past few years?
Not very well.
"It should be noted that perinatal mortality was unusually low on the Atlantic coast during the UME years, likely because there was not sufficient nutrition to support manatee reproduction, which skews the five-year average," deWit added of the five-year average of 35 perinatal deaths.
Are perinatal deaths natural?
Yes, but not always. Environmental stress can kill more manatees right after birth.
"Perinatal mortality naturally occurs in reproducing populations, and our carcass examinations have not shown any unusual causes in the dead calves that were necropsied," deWit said of this year's deaths. "However theoretically it is possible some females may face challenges with returning to successful reproduction after experiencing a reproductive pause from malnutrition."
What about reproductive rates?
Biologists say more data is needed. "Reproductive rates from population models will provide more insight, but it takes a few years before these data are available,” deWit said.
Which counties had the most perinatal deaths this year?
Brevard had 25 perinatal deaths so far this year, followed by Volusia County with 11 deaths and Lee County with 7 deaths. The rest were scatted throughout several other coastal counties.
What is the overall manatee death toll so far this year?
Through May 10, the most recent data available, there have been 257 manatee deaths in Florida, compared to 287 last year and a five-year average of 415 by this time of the year.
How does this year compare with previous years?
Despite the perinatal deaths, Florida has had its lowest overall number of manatee deaths since 2019, as the threatened species rebounds from a record die-off in 2021 that claimed at least 1,100 manatees statewide. Many of those manatees died near Merritt Island. By May 10 of that year, 730 manatees had already died.
How do this year's other causes of deaths break down?
This year's deaths included 34 by watercraft, one less than last year and five less than the five-year average. Also, 26 died this year of natural causes, nine from cold stress, 17 from undetermined/other causes, five from other human causes, and 98 dead manatees were not examined after death.
Which counties had the most manatee deaths?
So far this year, Lee County has had the most manatee deaths, 48, followed by Brevard with 37 deaths: 25 perinatal, one by watercraft, one "other human," four natural, three undetermined and two not examined.
How many manatees are there?
FWC estimates of statewide manatee population for the 2021-2022 period is 8,350–11,730 manatees, with 3,960–5,420 on the west coast and 3,940–6,980 on the east coast.
What do I do if I see a sick, injured of dead manatee?
Call FWC's Wildlife Alert Toll-Free Number: 1-888-404-FWCC (1-888-404-3922), press "7" to speak with an operator.
Contact Waymer at (321) 261-5903 or jwaymer@floridatoday.com.
