When “preserving our ecosystems” conflicts with endangered species needs: A manatee refuge in southwest Florida and Everglades restoration

Background/Question/Methods

Florida manatees (Trichechus manatus latirostris) are susceptible to “cold stress syndrome” after prolonged exposure to water temperatures <20°C, therefore a source of warm water is necessary for them to survive extended cold periods during the winter.

The largest warm water refuge in the Ten Thousand Islands (TTI; Collier County FL) is found in the Port of the Islands (POI) basin.  This basin retains heat when it receives fresh water flow over the FU-1 weir from the drainage system of the Southern Golden Gate Estates (SGGE), a failed subdivision created by the Gulf American Land Corporation in the 1960’s. 

The state of Florida purchased the SGGE to create the core of the Picayune Strand State Forest, and restore the area to its pre-drainage condition.  The objective of the Federally authorized Picayune Strand Restoration Project (PSRP) is to restore hydrologic sheetflow over approximately 240 square kilometers of wetlands, and is widely expected to improve habitat quality for several federal and state threatened and endangered species and species of special concern, such as Florida panthers, wood storks, bald eagles, and others.

Restoration activities upstream will reduce freshwater flow over the FU-1 weir, which will impact the warm water refuge that persists in many years at POI.  How would this impact the manatee population in the TTI?

Results/Conclusions

Analysis of historical water temperatures, flow rates over the FU-1 weir, and carcass recovery from the TTI showed a higher rate of manatee carcass recovery (as a proxy for mortality) in the POI basin and associated canals during periods of cold ambient temperatures that were coupled with low freshwater flow.  A predictive model showed that the number of carcasses recovered will increase as the number of cold days increases.  If flow over the FU-1 weir is low, then the rate of carcass recovery can be double the rate as when the flow is high.  The model suggests that the reduction of flow over the FU-1 weir caused by the PSRP will negatively impact the warm water refuge, and the manatees that depend on it.

How can managers reconcile the activities upstream, which restore wetland habitat, with the decrease in fresh water that supports the manatee refuge downstream?  A multi-agency task force is currently evaluating options to ensure continued protection of the manatees, including possible mitigating factors such as providing an alternate refuge for manatees in the TTI, without impacting the ongoing PSRP.