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 deceased manatees have been reported statewide to the Florida Fish and Wildlife Conservation Commission (FWC) in 2021.

444 manatee deaths have been reported within the Indian River Lagoon National Estuary watershed.

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

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's 292 manatee mortalities, 7% of the total east coast population, have met 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.

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 in the North Indian River Lagoon is estimated at 500 individuals, a 2016 aerial survey counted 1,400 winter manatees near the power plant outflow. During the winter, an estimated 35% of Florida's total east coast manatee population moves into the heated power plant discharge within the Port St. John compartment of the Indian River Lagoon.

Loss of Seagrass

The Indian River Lagoon has lost around 54% of the record high seagrass coverage recorded in 2007. This loss of seagrass is due to an excess of Phosphorus and Nitrogen nutrient pollution feeding algae blooms that block the sun, and inhibit the growth of seagrass.

Exasperating the lack of seagrass are manatees that may eat up to 10% of their body weight in seagrass daily. 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.

For example, lets assume that 1400 manatees with a average weight of 500lbs consume seagrass at the rate of 70,000lbs daily or 6.3m lbs during a 90 day winter stay. The visiting winter herd consumes the NIRL's sparse seagrass during their stay, and in spring, as the hungry herd begins to dissipate, they consume the year's emerging seagrass shoots roots and all.

Current "Word from the Water" is that the current 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 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 the PSJ compartment. What goes into it's water may remain for 7 - 8 months. As much as 700m gallons of the compartment's impounded, nutrient rich water is circulated through the plant's cooling system daily.

Considering that the visiting manatee herd might excrete half of the seagrass it eats, would amount to 35,000lbs per day, or 3.15m lbs per winter, increasing the North Indian River Lagoon's excessive nutrient load.

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.

The good news is that spring is here, the lagoon's water temperature has warmed up, and Brevard's wintering manatees are headed home until next year.

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