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

Indian River Lagoon News

Indian River Lagoon Manatee Mortality Update

IRLNews, Author

April 28, 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. Manatees were reclassified from an endangered to a threatened species under the federal Endangered Species Act in May, 2017.

As of April 23 a record 696 deceased manatees have been reported to the Florida Fish and Wildlife Conservation Commission (FWC) in 2021.

The Indian River Lagoon National Estuary watershed has reported 444 manatee deaths to the FWC so far this year.

2021 IRL Manatee Deaths

County	2/26/2021	3/26/2021	4/23/2021
Volusia	16	26	51
Brevard	168	248	292
Indian River	13	21	20
St. Lucie	4	11	12
Martin	24	31	34
Palm Beach	29	34	35
Total	254	371	444

Brevard County Manatee Mortality

1040 manatees at Port St. John power plant in 2016

Brevard County citizens reported 292 manatee deaths to the FWC this year. Brevard's 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.

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.

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.

Video

Virginia Barker, Brevard Natural Resources Management Director, speaks about the record manatee deaths in the north IRL.

Video courtesy of Brevard Indian River Lagoon Coalition

Web Links

• Bloomberg Businessweek: Nobody Knows How to Wean Manatees Off of Power Plants
• FPL customers pay to keep manatees cozy and alive - Orlando Sentinel
• FWC - Summary of Warm Water Refugia Issues
• FWC: Manatee Mortality Event Along The East Coast: 2020-2021
• NOAA Marine Mammal Unusual Mortality Events
• Winter Manatee Foraging Behavior and the Decline of Seagrass Beds in the Northern Indian River Lagoon USGS 2015
• FWC Update to the Statewide Florida Manatee Abundance Estimate

Documents

• FWC 2021 Preliminary Manatee Mortality Table (PDF 19pp 562KB)
• FWC 2021 YTD Manatee Mortality Table (PDF 1p 113KB)
• Updated Statewide Abundance Estimates for the Florida Manatee (PDF 27pp)

References

Location: Estuary: Indian River Lagoon: Florida East Coast

Source: Article Published by Indian River Lagoon News on April 28, 2021. Retrieved on April 28, 2021.

Topic: Wildlife