Abstract
A decline in submerged aquatic vegetation (SAV) within Florida's spring-fed, thermal refuges raises questions about how these systems support winter foraging of Florida manatees (Trichechus manatus latirostris). We analyzed telemetry data for 12 manatees over seven years to assess their use of Kings Bay, a winter refuge with diminished SAV. After accounting for the effect of water temperature, we hypothesized that the number of trips out of Kings Bay would increase and the time wintering manatees spent in Kings Bay would decrease. Trips out of and into Kings Bay also were compared to assess potential influences on exiting or entering. There were no detectable differences in the number of trips out of the bay or overall time manatees spent in Kings Bay across winters. The percentage of time water temperatures were below 20°C was the single best predictor of increased time spent in Kings Bay. Trips out of Kings Bay were more likely to occur after 12:00 h and during a high but ebbing tide, compared to trips into the bay. Nine manatees tracked for longer than 75 days in winter spent 7-57% of their time in the Gulf of Mexico, and three of these manatees spent 7-65% of the winter >80 km from the mouth of Kings Bay. Results suggest the low amount of SAV in Kings Bay does not obviate its use by manatees, though there are likely tradeoffs for manatees regularly foraging elsewhere. Accounting for movements of Florida manatees through a network of habitats may improve management strategies and facilitate desirable conservation outcomes.
Highlights
Many marine and coastal ecosystems are changing due to climate change, habitat degradation, or other anthropogenic stressors (Lotze et al 2006, Waycott et al 2009, Hoegh-Guldberg & Bruno 2010)
We focused on the recovering population of Florida manatees Trichechus manatus latirostris
We evaluated the potential effects of winter year (WYR), gender (SEX), water temperature (TEMP), manatee size (SIZE), tide stage (TIDE), time of day (6HR), and gage height (GAGE) relative to the North American Vertical Datum of 1988 (NAVD 88) on the number of hours spent in Kings Bay, number of aggre
Summary
Many marine and coastal ecosystems are changing due to climate change, habitat degradation, or other anthropogenic stressors (Lotze et al 2006, Waycott et al 2009, Hoegh-Guldberg & Bruno 2010). Manatees in the Northwest Florida management unit exist near the upper end of the latitudinal range for the genus, and they exhibit temperature-mediated seasonal movements in response to cooler temperatures (Hartman 1979) This type of temperaturedriven movement between habitats has been observed in dugongs Dugong dugon (Holley 2006, Marsh et al 2011), which highlights the importance of multiple habitats in sustaining healthy sirenian populations (Castelblanco-Martínez et al 2009, Alvarez-Aléman et al 2017, Haase et al 2017). The loss of suitable SAV near warm-water sites may be causing manatees to leave winter refuges more frequently or for longer durations, resulting in prolonged exposure to cold temperatures To investigate this issue, we analyzed telemetry data for Florida manatees wintering in a system that provides ample thermal refuge but limited food. Historical data indicate clearly that Florida manatees have consistently relied on Kings Bay and nearby offshore areas as a source of food throughout the year and as Littles et al.: Wintering manatees confronting less freshwater SAV
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