The Effects of a New Bridge on Manatee (Trichechus manatus latirostris) Use of the FPL Discharge Canal at Port Everglades, Florida

The Florida Manatee (Trichechus manatus latirostris) migrates to warm water refuges during the winter months to escape cold water. One such refuge is the effluent canal from the Florida Power and Light electrical plant in Port Everglades, FL. Construction of a new bridge over FPL effluent canal may affect manatee abundance in this area. We compared age class and cow/calf abundance counts during pre-bridge winter 2009 with data from winter 2010, during construction, and winter 2011, post-construction. No manatees were present until surface water temperatures fell below 22° C. Although monthly mean surface water temperatures were not statistically different (p = 0.2) between winter 2009, 2010 and 2011 (21.9 ± 0.4° C, 21.8 ± 1.8° C and 21.4 ± 0.6° C respectively), manatee abundance varied. Winter 2009 had higher mean numbers of manatees per survey from December through March (29.7 ± 12.2, 27.4 ± 49.9, 48.1 ± 43.2, 2.0 ± 4.0, respectively) than winter 2010 (0.0 ± 0.0, 30.1 ± 24.2, 10.7 ± 8.5, 5.0 ± 5.0, respectively) and winter 2011 (18.7 ± 12.8, 6.7 ± 26.8, 0.1 ± 0.3, 0.0 ± 0.0). Neither mean water temperatures pre- and post-construction (21.8 ± 0.3° C vs 21.4 ± 0.5° C, respectively) or mean number of adult manatees pre- and post-construction (23.8 ± 17.1 vs 4.14 ± 5.8, respectively) were significantly different. An ANOVA demonstrated significant differences (p = 0.02) between age classes in 2009, but no significant differences were found in 2010 and 2011. While it does not appear that bridge construction at Port Everglades reduced the number of overwintering manatees in 2010, the impacts of construction projects in manatee aggregation areas must be included in conservation planning for this endangered species