The seasonal distribution of the Florida manatee (Trichechus manatus latirostris) is influenced predominantly by feeding locations in the summer and proximity to warm-water refuges during colder months. Due to their limited ability to tolerate cold water, when water temperatures drop below 20°C manatees congregate around natural and artificial warm-water refuges, such as warm-water springs or power plant outfalls. Distribution may further be influenced by the tidal cycle through its impact on manatee movement and foraging. Although the importance of tide on manatee distribution and habitat selection has been acknowledged, it has yet to be studied quantitatively in respect to the manatee population in southeast Florida. The purpose of this study was to examine the effect of the tidal cycle on manatee occurrence at the Florida Power & Light (FPL) Port Everglades Power Plant. Walking surveys were conducted in Port Everglades during manatee season, November 15 – March 31, between 2004 and 2008. During the surveys, the number of manatees in four established locations was noted and the animals categorized based on size as either calf, juvenile, or adult. Water temperature data were also collected at four permanent sample locations. Because many surveys yielded zero manatees observed, data were analyzed using the zero-inflated negative binomial model. Although the manatees at the Port Everglades Power Plant must forage away from the warm-water refuge, my findings show no correlation between tidal state and total manatee occurrence at the FPL Port Everglades Power Plant. The results do, however, suggest that the probability of observing a cow/calf pair is greater during high tide when compared to low and mid-tides (P < 0.05). Total manatee occurrence and the presence of cow/calf pairs were both significantly correlated with water temperature (P < 0.05).

Florida manatees (Trichechus manatus latirostris) seek out warmer waters during winter months when ambient water temperatures drop below 20 degrees Celsius. Over time, manatees have discovered artificial warm water sites from power plant discharges in addition to natural sites such as springs and passive thermal refugia (PTRs). The Florida Power and Light (FPL) Port Everglades power plant in Broward County is one such artificial warm water refuge used by manatees. This plant was shutdown on July 16, 2013, and is expected to remain off line for at least three years during demolition and construction of a new facility. The purpose of this study was to determine changes in habitat usage and other responses to the disruption of a warm water refugia (the closure of a power plant) on Florida manatees within the greater Port Everglades region. From November 15, 2013 to March 31, 2014, manatees were counted at the site via shore line and aerial surveys. Environmental data were collected to determine variables correlated to manatee presence and absense. Two manatees were radio-tagged using remote sensing devices in an effort to identify alternative warm water refugia and feeding areas. Data were collected from state and local organizations and photo-identified manatees were used to analyze for trends in cold stress syndrome (CSS) lesions and watercraft scarring. Results confirmed that manatee presence was positively correlated with heater outlet temperature. Differences did not exist between the results of survey methods between the FPL Port Everglades (PE) and Fort Lauderdale (FL) power plant sites, however, differrences in the aerial survey counts showed an increased presence at the FL site during the colder month of January 2014. Data from tagging identified one manatee that preferred the FL site while another preferred PE, presumably due to more convenient access to feeding grounds in Biscayne Bay. Data from mortality events indicated a low number of CSS and watercraft deaths in Broward County as compared to other parts of the state of Florida. Further monitoring of the study area for the remainder of the shutdown period is recommended, as are improvements in survey design, expansion to include additional environmental data from FL, continued mortality statistic analysis and locating possible PTRs.

The largest Florida manatee (Trichechus manatus latirostris) aggregation at a natural warm-water refuge occurs in Kings Bay, Crystal River, FL. Over the last 32 years, the U.S. Fish and Wildlife Service and the State of Florida have created a network of manatee protection areas within Kings Bay including a year-round refuge designation and seven Federal manatee sanctuaries during the winter manatee season (November 15 – March 31). Aerial survey data collected between 1983 and 2012 was used to examine the seasonal change in manatee distribution within Kings Bay in order to assess the effectiveness of current sanctuary sizes and locations. Regression analysis indicated a significant change in manatee abundance among the winter seasons (p < 0.05). The average winter manatee counts increased by 4.81 animals per year over the 30 year period. In contrast, no significant changes in average or peak manatee abundance was detected among the summer seasons (p = 0.71 and p = 0.45 respectively). The average manatee counts increased by only 0.109 animals per year over the summer periods. Spatially explicit models using Geographic Information System (GIS) analysis revealed a strong correlation between high manatee density and artesian springs during the winter seasons. Highest abundances were identified at three locations: King’s Spring, Three Sisters Springs, and Magnolia Springs. These three locations coincide well with pre-existing sanctuary designations, but additional coverage is needed to support the overflow of manatees outside of sanctuary boundaries. Manatees continued to use Kings Bay in the summer seasons but in lower numbers and densities. Because density patterns were not uniform across summer periods, a heavier reliance on boat speed regulation is recommended to provide adequate protection to the endangered Florida manatee. Within a habitat type, the Magnolia Springs, South Banana Island, and Three Sisters Springs sanctuaries exhibited a significant influence on manatee density, suggesting differences in quality among sanctuaries. Years coinciding with extreme cold weather events also had a significant influence on manatee density. Using GIS to investigate seasonal shifts in manatees can be very informative regarding many issues including habitat selection and may improve the design and management of protected areas.