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

An estimated 11% of Florida's total East Coast manatee population has expired in the IRL so far this year.

2021 IRL Manatee Deaths

County	2/26	3/26	4/23
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

444 manatee deaths have been reported within the Indian River Lagoon National Estuary watershed, meeting the criteria to be declared an Unusual Mortality Event (UME) by the Working Group on Marine Mammal Unusual Mortality Events. The 2021 Florida Atlantic Coast Manatee UME is the 71st declared under the Marine Mammal Protection Act since 1991.

This is not the Indian River Lagoon's first Unusual Mortality Event.

• Florida East Coast Manatee UME #58 was declared by NOAA Fisheries in 2013, and remains on the active list with cause "Undetermined".
• UME #59 was declared in 2013, after 79 Bottlenose dolphins expired due to "Ecological Factors".
• UME #46, 2008, 48 Bottlenose dolphins expired due to "Undetermined" cause.
• UME # 19, 2001, 30 Bottlenose dolphins expired due to "Undetermined" cause.

Of the seventy one Marine Animal UMEs listed by the NOAA since 1991, FIVE have occurred within the Indian River Lagoon.

Brevard County Manatee Mortality

1040 manatees at FPL power plant.

Brevard County, with 292 reported mortalities, is GROUND ZERO for Florida Manatee UME #71. There are many factors affecting Brevard's marine animals. All due to human impact.

Migration Interruption

During the winter manatees congregate in the Port St. Johns compartment of the NIRL due to the power plant's warm water discharge. 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 area's resident manatee population is estimated at 500 individuals, a 2016 survey counted 1,400 winter manatees near the power plant's outflow. During the winter, an estimated 35% of Florida's total east coast manatee population moves into Port St. Johns heated power plant discharge in the North Indian River Lagoon.

Loss of Seagrass

The IRL estuary has lost around 54% of the record high seagrass coverage recorded in 2007. This loss of seagrass is due to excessive nutrient pollution feeding algae blooms, that block the sun, and inhibit the growth of seagrass.

Further limiting Brevard's seagrass growth, are manatees that may eat up to 10% of their body weight in daily. For discussion's sake, let's assume 1400 visiting manatees, with a average weight of 500lbs, eat 70,000lbs daily or 8.4 million pounds of seagrass during a 120 day winter stay. Even with perfect water quality the PSJ compartment of the North IRL could not produce enough seagrass to support the huge visiting manatee population attracted to the power plant's warm discharge every winter.

The visiting winter herd consumes all of NIRL's seagrass during their stay, and in spring, as the starving herd begins to dissipate, consume the year's emerging seagrass shoots roots and all. The recent "Word from the Water", is that the lack of rain has greatly improved water clarity, which is unfortunately, revealing a sparse barren desert from Titusville south to Cocoa.

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 NIRL compartments is impeded on the north by SR405 NASA Causeway (82% constriction), and to the south by SR528 Merritt Island Causeway (73% constriction). Water flow blocked by these earthen berm dams adds to the water's estimated 220 day residence time.

Hard embankments on the west shore and mosquito impoundments on the east eliminate the lagoon's natural filtering system. What goes into North Indian River Lagoon water may remain for 7 - 8 months.

Assuming that a visiting population of 1400 manatees might excrete half of the seagrass it eats, amounts to 35,000lbs per day, or 4.2 million pounds of excrement during a 120 day winter stay.

Port Saint John's water is well blended as up to 700 million gallons of it's nutrient laden water circulates through the plant's cooling system each day.

Conclusion

Florida has reached the point where power utilities have to provide temporary pumps and heaters to continue the manatee's dependence on power plant outflows. If a plant is decommissioned, the power company must continue providing heated water to it's dependent manatees indefinitely. If a plant shuts down unexpectedly and the heated discharge stops, the visiting manatee population may suddenly expire due to cold exposure.

The obvious solution to Brevard's visiting manatee problem is to gradually eliminate the plant's thermal pollution by reducing it's discharge temperature during the winter months. The manatees will eventually return to their natural migration pattern, and lessen their impact on NIRL's seagrass and water quality.

The good news is that spring is here, the lagoon's water temperature is rising, and Brevard's visiting manatees are headed home until next winter.

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

• Marine Mammal Commission: Manatees and Warm-Water Refuges
• E&E News: Manatees and power plants
• 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
• Winter Manatee Foraging Behavior and the Decline of Seagrass Beds in the Northern Indian River Lagoon USGS 2015
• FWC: Manatee Mortality Event Along The East Coast: 2020-2021
• NOAA Marine Mammal Unusual Mortality Events
• 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