Possible Causes of the Manatee Deaths in the Mud River

Over the winter, there has been a great deal of concern and confusion regarding wildlife, namely manatees, in the waterways along Hernando County’s coast. In recent issues, the Sun has delved into why the five sea cows were found dead in the Mud River earlier this year. The latest manatee death count from the Florida Fish and Wildlife Commission (FWC) is six.

In 2023, there was one death recorded by the FWC. In 2022, there were a total of 5 manatee deaths, none having occurred within the first four months of the year. 2021 saw two manatee deaths attributed to watercraft.

Citizens shared these worries at local county meetings. While some opined that it may have been due to boat propellers, studies found that it was due to the manatees’ sudden change in diet when their supply of eelgrass died out. Rob Hazelton, who operates the local Weeki Wachee Boat Rentals, wanted to set the record straight to assuage any public concerns that may still be present.

“Obviously, I live on the river, so I very much care about the health of the river,” said Hazelton. “My kids use it, and I got grandkids now. I do not want to be the last guy to use it. That would be horrible. We want to maintain the health of the river and the whole ecosystem […] I try to make sure we try to [rent boats] responsibly.”

Hazelton’s rental service accomplishes this through multiple means. The company puts prop guards, also referred to as “manatee guards” by Hazelton, on every single vessel that is taken out onto the waterways. His boats are also equipped with new, eco-friendly motors that output “super low emissions” to cut down on footprint. His business will often go the extra mile in its dedication to river conservation by having employees ride along with renters to ensure the safety of the river and its inhabitants.

When Idalia roared across Florida’s west coast in August of 2023, it dumped thousands of gallons of saltwater into the freshwater rivers and tributaries. Hazelton, who has operated his rental business for the last five years, had never seen the canal by Italian eatery La Bella Napoli flooded. For “8 to 12 hours,” water had risen to near-house levels during the pounding storm. He then noticed that all the eelgrass that lined the local waterways had died within about a week’s time.

“The manatees came in there and fed all the time,” said Hazelton. “The saltwater was just up in there for so long and […] it would take a few high tide-low tide cycles to get all that saltwater out of that.” With other waterways suffering similar fates, the manatees ran out of eelgrass to eat and began to perish after the addition of macroalgae to their diet. Local canal resident Stacy Vu echoed Hazelton’s sentiments when she noticed the change in vegetation, but fortunately, these plants seem to be returning to the river.

“[The eelgrass] used to be a couple of feet tall all around our dock,” Vu said. “We used to have manatees feeding there basically every day and probably a week after the hurricane, it was just gone all the way down the canal. We have sprigs of it starting to pop back up and starting to grow back again […] I see it come back now. It is three inches long […] at least in our canal off of our dock.”

University of Florida Institute of Food and Agricultural Sciences UF/IFAS Marine Extension Agent Brittany Scharf stated that the eelgrass is vulnerable to turbidity in the water. In addition, the eelgrass variety in the Weeki Wachee Rivers is sensitive to high salt levels. Both of these conditions existed after the significant storm surge of Hurricane Idalia, the water being cloudy, opaque, and thick with suspended matter and the water having high levels of salt. These conditions stressed and killed much of the eelgrass.

Scharf also mentioned that before the COVID-19 pandemic, UF/IFAS was growing eelgrass. Now, they are growing seagrass.

Homeowners along the river cannot supply food for the manatees, as feeding manatees is illegal. On the East Coast, the Florida Fish and Wildlife Commission had a trial feeding program for starving manatees that ended in December 2023.

With the normal source of food no longer being plentiful, the manatees had to switch to different food sources. This abrupt change can lead to gastric distress and manatee death.

Crystal River Eelgrass Restoration

A similar issue happened in Crystal River with the No Name Storm in March 1993. Saltwater inundated the river system, killing all of the plants and allowing the proliferation of Lyngbya, an invasive blue-green algae that forms mats of vegetation along the riverbed. Lyngbya will kill and prevent the growth of native aquatic plants.

An organization called Sea and Shoreline has worked to reverse the damage and actively restore bodies of water to healthy states. The organization has a team of roughly 100 people and has been carrying out this line of work for two decades. Chief Sales and Marketing Officer at Shoreline, Heather Herold, spoke with the Sun on how the company partners with cities, counties, and non-profits to carry out these gargantuan restoration efforts.

“We have a model that we follow to help reset ecosystems,” said Herold. “So, part of that in the process is just garnering support from local residents, local stakeholders, the county, the water management district. There may be a non-profit in the area that is looking to restore a water body […] We have experts, including biologists and marine construction experts, that can look at a water body, analyze it, survey it, and create essentially a scope of work for that project. Then, we work on permitting it. We also work on raising the funding for that project.”

The organization has been working on Crystal River since 2014 to undo the damage caused by the No-Name Storm in the 1990s. Some projects are longer than others; it just depends on the scope of the project, largely determined by the amount of available funding. If Hernando County has a problem water body, like those suffering from eelgrass shortages along the coast, Sea and Shoreline has a model where “we can go in and dredge out any muck or remove invasives and get to clean sediment, and then we plant native submerged vegetation. Then, it sort of takes over and expands throughout the water body,” Herald said.

Eelgrass and other native plantlife is the foundation to life in a body of water as it helps to cycle out excess nutrients and clean and oxygenate the water. The importance of vegetation goes beyond this as it also reduces algal blooms, creates habitat and food for fauna, stabilizes sediment and stores carbon. “Submerged aquatic vegetation is critically important to a water body,” said the chief sales and marketing officer.

The habitat creation and restoration organization receives its funding through legislative appropriations and has already restored 100 acres of the Crystal River. In doing so, the project reached a “tipping point” where nature began to heal itself. This estimate expands the acreage to 400. They are currently working on the Homosassa River and planning to move into the Rainbow River as well.

The state is investing in water and the environment in Florida, noted Herold, since “people come to Florida for the water.” Hernando would likely be interested in aquatic preservation for the same reasons as the state, such as ecotourism, property values, and a healthier environment in general. If the county is looking for a project of this magnitude to be carried out, Herold said, “We are more than happy to speak with them and would love that opportunity.”

Unusual Tides

Another boat captain who preferred to stay anonymous posited a different possible cause of the Mud River manatee deaths. The manatees gather in the rivers for warmth during the winter as the Gulf becomes colder. The manatees venture out of rivers to the Gulf to feed as the day warms up and return as the day cools off. It is common to see manatees heading into the Gulf around 10 am and returning around 3 p.m.

He stated that the tides this winter were reversed from normal. Usually, the high tide comes during the hot part of the day, but this year, the low tide has been during the day. This means that the manatees would not be able to leave the river to feed in the Gulf during the hot part of the day. The manatees would not be able to go later because it would be too cold. This means that they had to do more foraging in the river. The Mud River has lots of algae and eating too much of this too quickly could have caused their gastric distress.

He also commented that this year, he was seeing many fewer manatees in the area.