Manatee deaths approach morbid milestone

Some experts link spike to pollution killing off the animals’ food supply

Florida’s record year for manatee deaths is approaching 1,000, according to data from the Florida Fish and Wildlife Conservation Commission.

There have been 957 manatee mortalities reported through Sept. 24, with most of them coming from the beginning of this year.

Although complete monthly numbers are not tabulated, initial data shows September had the lowest mortalities of the year with 25 deaths. The most common probable causes of death were watercraft collisions, natural causes and “non necropsied” or uncertainties. Lee and Pinellas counties had the most deaths, with seven each in September.

The causes of mortality fluctuate yearly. Some years are bad for watercraft-related deaths, as was the case in 2019, which saw 137, and some years are bad for natural deaths, like in 2018 with 233.

The largest cause of death for 2021 is listed as “non-necropsied,” meaning the deaths were confirmed, but no examination for a cause of death was done. Experts believe this unprecedented spike was brought on by pollution killing off the manatees’ food supply, causing starvation.

About one-third of these deaths were considered calves, young manatees heavily dependent on their mothers.

Cold stress is an affliction that typically affects small manatees that have drifted into colder waters. It can be a common cause of death in years when there are record cold temperatures.

2010 saw an especially brutal cold spell, one that was responsible for killing 282 manatees to cold stress, 37% of the mortalities that year.

Manatee deaths from watercraft have lowered significantly during the pandemic but increased slightly this year. Watercraft deaths occur when the blunt force of a boat or jet ski hits the creature, potentially breaking ribs and causing organ damage, or when the propeller of a watercraft cuts deep into tissue.

Brevard and Lee counties are the most common area for these deaths.

Watercraft deaths are most likely in counties with large manatee populations and many registered boats. According to 2020 statistics from the Florida Highway Safety and Motor Vehicles, Brevard County has the seventh-highest number of vessels in the state with 34,689. Lee County has the third-highest number of vessels with 49,611.

While Brevard and Lee County have the highest number of watercraft deaths, they also have the highest confirmed mortalities in total.

“Simply put, more manatee carcasses are expected in areas where there are more manatees and where they die at a higher rate.” said Chip Deutsch, a research scientist with the Fish and Wildlife Research Institute “Brevard and Lee Counties have historically provided excellent habitat for manatees year-round and that attracts more manatees than most other counties.”

Every so often, the Florida Fish and Wildlife Conservation Commission does aerial surveys to gauge how many manatees are in Florida waters. These surveys are limited to the winter, as the cold brings the manatees to warmer, more visible waters.

The trend shows that the manatee population has increased massively since the first survey done in 1991, enough for the U.S. Fish and Wildlife Service to downlist the “sea cows” from endangered to threatened in 2017.

Putting into perspective the number of mortalities against the estimated manatee population, we see the number of deaths increase with the population of manatees, but with no aerial survey for 2021 it is uncertain as to how this especially bad year will affect the manatee population.

Spikes in mortalities in 2010 and 2018 resulted in a lower reported manatee population the following year, meaning this year’s casualties could set the manatee population back even more, undermining years of progress.