IRLNews:2021-04-01/Indian River Lagoon Manatee Mortality Update

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An Unusual Mortality Event (UME) has been declared as Brevard's Indian River Lagoon manatees starve to death at a record rate, due to the depletion of seagrass, and the interruption of their natural migration.
Indian River Lagoon News
Indian River Lagoon Manatee Mortality Update
IRLNews, Author
April 1, 2021
Indian River Lagoon -
In 2016 there were an estimated 8,810 Florida manatees, 4,810 on the west coast and 4,000 on the east coast.[1] Manatees were reclassified from an endangered to a threatened species under the federal Endangered Species Act in May, 2017.[2]

As of March 26, 2021, a record 573 deceased manatees have been reported to the Florida Fish and Wildlife Conservation Commission (FWC) this year.[3]

Florida Manatee Mortality 2016-2021
Florida Manatee Mortality Report

The Indian River Lagoon National Estuary watershed has reported 371 manatee deaths to the FWC so far this year.[4]

2021 IRL Manatee Deaths
County 2/26/2021 3/26/2021
Volusia 16 26
Brevard 168 248
Indian River 13 21
St. Lucie 4 11
Martin 24 31
Palm Beach 29 34
Total 254 371

Brevard County Manatee Mortality

1040 manatees at Port St. John power plant in 2015

In the first 85 days of 2021 Brevard County citizens reported 248 manatee deaths to the FWC. These manatee mortalities have met the criteria to be declared an Unusual Mortality Event (UME) by the Working Group on Marine Mammal Unusual Mortality Events, and the U.S. Fish and Wildlife Service has confirmed the UME determination.

There are many factors affecting Brevard's manatee population. All due to human impact.

Natural Migration Interruption

During the winter manatees congregate in the Port St. Johns compartment of the North Indian River Lagoon due to the warm water discharge from the power plant. Manatees would normally migrate south as the water temperature drops, but the power plant's warm water outflow distracts them from their natural migration. While the resident manatee population is estimated at 500 individuals, a 2016 aerial survey counted 1,400 winter manatees in the PSJ compartment of the North IRL.

Loss of Seagrass

It is estimated that the Indian River Lagoon has lost 54% of the record high seagrass coverage recorded in 2007.[5]

Manatees may eat up to 10% of their body weight daily. Even with perfect water quality the PSJ compartment of the North IRL could not possibly produce enough seagrass to support the huge visiting manatee population attracted to the power plant's warm discharge. For example, lets assume that 1400 manatees with a average weight of 500lbs might consume seagrass at the rate of 70,000lbs daily or 6.3m lbs during a 90 day winter.

Water Quality in the PSJ Compartment

The Port Saint John compartment has no inflows other than nutrient laden stormwater run-off. The exchange of water with other IRL compartments is impeded on the north by SR405 NASA Causeway (82% constriction), and SR528 Merritt Island Causeway (73% constriction) to the south. Hard embankments on the west shore and mosquito impoundments on the east eliminate 100% of the lagoon's natural filtering systems.

The lack of water exchange causes an estimated 220 day residence time in this compartment. What goes into the lagoon may remain for 7 - 8 months. However, the PSJ compartment is well blended, because the plant's cooling system circulates as much as 700m gallons of it's impounded water daily.[6]

Assuming that Brevard's visiting manatee herd excretes half of the seagrass it eats, amounts to 35,000lbs per day, or 3.15m lbs per winter, added to the PSJ compartment's nutrient load.

The good news is that the Indian River's water temperature is warming up, and the manatees are dispersing to more fertile areas.

Contact FWC Wildlife Hotline at (888) 404-3922 to report a deceased manatee.

Location: Estuary: Indian River Lagoon: Florida East Coast
Source: Article Published by Indian River Lagoon News on April 01, 2021. Retrieved on April 01, 2021.
Topic: Wildlife
Poster: AdminPosted: 04/01/2021
Indian River Lagoon News - 2021-04-01/Indian River Lagoon Manatee Mortality Update
An Unusual Mortality Event (UME) has been declared as Brevard's Indian River Lagoon manatees starve to death at a record rate, due to the depletion of seagrass, and the interruption of their natural migration.