New threats to the Florida manatee raise conservation concerns

Are we doing enough to protect Florida’s favorite marine mammal?

Article and pictures by Dani Sattelberger

When you think of Florida, the idea of beautiful beaches amidst world-famous theme parks may come to mind. As divers, we envision the coral reefs off the Keys or crystalline-clear water of the Florida springs, along with the wildlife that inhabit these areas. Among the unique wildlife in Florida, is the manatee, the iconic, herbivorous marine mammal dubbed “gentle giant” that resides in the shallow coastal waters across the state. Every year, eco-enthusiasts head to areas like Crystal River to enter the water for an up-close encounter with these friendly creatures. Unfortunately, these lovable sirens are facing continued and novel threats to their long-term survival in the Sunshine State.

Are we doing enough to protect Florida’s favorite marine mammal?

Florida’s Threatened Marine Mammal

In the United States, the U.S. Fish and Wildlife Service (USFWS) oversees the management and recovery plans of endangered and threatened species like the West Indian manatee (Trichechus manatus). In 2017, the USFWS reclassified the status of manatees in the United States from endangered to threatened under the requirements listed in the Endangered Species Act (ESA) of 1973 after reviews of scientific research and population surveys (Runge et al. 2017; USFWS 2017). This reclassification action impacted two subspecies of the West Indian manatee endemic to the United States, the Florida manatee (Trichechus manatus latirostris) in Florida and the Antillean manatee (Trichechus manatus manatus) in Puerto Rico but maintains protections and existing critical habitat. Per requirements of the ESA, a status review is required every five years to determine possible changes to downlist, as what happened in 2017, or uplist (reclassify) for species listed under the Act.

While manatees are still protected under federal, state and territorial laws (USFWS 2001, 2017; Allen et al. 2014), there is a growing urgency to address severe, immediate impacts to the manatee population in the United States. A recent article in the Latin American Journal of Aquatic Mammals, highlights how these beloved marine mammals continue to face new and growing threats from direct and indirect anthropogenic impacts and a growing common trend of large-scale mortality events related to climate change.

A New Threat to Manatees

An unusual mortality event (UME) is distinguished as a significant die-off of any marine mammal population that “demands immediate response”. Currently, along the east coast of Florida, is an ongoing UME, impacting manatees (NOAA 2024) that is centered around the Indian River Lagoon (IRL). The IRL is a large, biodiverse estuary along Florida’s Atlantic coast which is a critical habitat for manatees. Presently, the IRL is facing a major crisis, having lost > 50% of seagrass resources within the estuary since 2011 (Morris et al. 2021), as a result of a series of harmful algal blooms (HABs). These blooms are driven by anthropogenic nutrient sources like fertilizer, agriculture,

and septic runoff (Lapointe et al. 2023), which lead to poor water quality. The harmful algal blooms caused hypoxic (low dissolved oxygen) conditions and resulted in an increase in turbidity and low light conditions throughout the waters of the IRL, shading out light needed for seagrass to grow (Morris et al. 2021). As a result, manatees along the east coast of Florida are facing a new peril from a decline in food availability, as climate change is fueling an increase in harmful algal blooms.

Since seagrass is the primary source of food for manatees, manatees in the IRL have shifted their diet from consuming seagrass to consuming algae (Allen et al. 2022). Presently, the overall individual health consequences of this dietary shift in manatees are not known, but investigation into the nutritional composition of what manatees are eating could provide further insight into the potentially harmful aspects of malnutrition. In nature, when animals do not obtain the proper nutrition from food sources, there are underlying development issues that can affect the reproduction and survivorship of a species (Rosen & Trites, 2000; Osterblom et al. 2008), and the observed decline of valuable aquatic resources in the IRL can potentially occur under similar ecological conditions in other Florida waterways.

What is being done?

The Florida Fish and Wildlife Conservation Commission (FWC) runs a 24-hour hotline for the public to report sick and injured marine mammals (USFWS 2001, 2017). This agency works to rescue (when possible) and recover deceased manatees to perform necropsies (animal autopsies) on carcasses to determine the causes of mortality across the state (NOTE: call 1-888-404-FWCC if you see a sick, injured, or dead marine mammal). In 2021, Florida manatees reached their highest ever annual mortality total of 1,100, which exceeded the previous record of 830 in 2014; in 2022, another 800 deaths were recorded. While this number declined in 2023 to 556 fatalities, almost 2,500 manatee deaths were recorded in the last three years (manatee mortality data sources: FWC 2024a, 2024b, 2024c).

Unfortunately, manatees are a slow reproducing species, with one calf born to females every 1–3 years, and twin births being rare. In addition to the new danger discussed, manatees still face continued threats from marine debris (Reinert et al.2017), habitat loss and degradation, and the most well-known cause of mortality, watercraft strikes (Runge et al. 2017; FWC 2024a, 2024b, 2024c), which remains inadequately addressed. A deeper investigation is needed to understand the latest trends of manatee mortalities in Florida and highlight new and emerging patterns related to depletion of their food sources. Furthermore, consideration by the USFWS to re- evaluate the present conservation status of the West Indian manatee in the United States is pertinent considering the recent ongoing and increasing mortality trends. As individuals, we need to make efforts to conserve water resources, improve water quality by reducing nutrients entering waterways, clean up debris, protect critical habitat, and make a concerted effort to restore and rehabilitate Florida’s coastal ecosystems. Our immediate action is necessary to ensure that manatees remain an iconic species in Florida for years to come.