East Florida Warm Water Refuges IMMA

Criterion A – Species or Population Vulnerability

The West Indian Manatee (Trichechus manatus) as a species has been listed as Endangered on the IUCN Red List of Threatened Species (Deutsch and Morales-Vela 2024).   The Florida Manatee (Trichechus manatus latirostris) is a sub-species of the West Indian manatee that has not yet been assessed by the IUCN Red List.

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

The IMMA includes the Indian River Lagoon, one of the largest stocks of BSE (Bays, Sounds and Estuaries) stocks of common bottlenose dolphins (Tursiops truncatus) in the southeastern U.S. The best available population estimate is 1,032 individuals (95% CI 969-1,98; CV=0.03; Durden et al., 2021). Long-term residency has been documented through decades of photo-identification studies in the Indian River Lagoon (Odell and Asper, 1990; Titcomb et al., 2015), although movements outside of the lagoon are frequent (Odell and Asper, 1990). However, it is clear that the population in the lagoon is distinct from neighbouring coastal stocks (Mazzoil et al., 2011). Multiple communities of bottlenose dolphins are present, but more research is needed to understand the movements and fine-scale community structure within the area (Titcomb et al., 2015).

Sub-criterion B2: Aggregations

Aerial surveys to estimate abundance of manatees in Florida conducted in 2021-2022 (https://myfwc.com/research/manatee/research/population-monitoring/synoptic-surveys/) yielded an estimate of 9,790 of which 3,060-4,280 occurred on the east coast of Florida within the waters of the IMMA (Gowan et al., 2023). Manatees are vulnerable to cold stress and death, thus their survival depends on the use of warm-water refuges resulting from discharge of power plants and passive thermal basins, springs, creeks, and dredged canals, particularly in inland freshwater bodies, and on the presence of seagrass meadows (Laist et al., 2013; Valade et al., 2020). Long-term monitoring through aerial surveys indicates the presence of aggregations (50 to more than 500) of Florida manatees at key wintering sites in the IMMA (Laist and Reynolds, 2005; Laist et al., 2013) including St Johns River, Cape Canaveral, Port Everglades and Blue Springs State Park (Deutsch et al., 2003; Martin et al., 2015; Gowan et al., 2023). These areas serve as winter aggregation sites for more than half of the east coast population and serve as the primary feeding habitats for the east coast population of the subspecies (Laist et al., 2013; Gowan et al., 2023; Valade et al., 2020). Martin et al. (2015) estimated that 70% of the east coast manatee population were in Brevard County during a coast-wide survey in March 2012. Along the coastline, extensive seagrass meadows provide the main feeding grounds for this species. Manatees primarily forage on Halodule wrightii and Syringodium filiforme, which are concentrated in intracoastal waters around the State, from the Indian River Lagoon to the Florida Keys (east to south), (Zieman & Zieman, 1989; Allen et al. 2022).