Graduation Year


Document Type




Degree Granting Department


Major Professor

Henry R. Mushinsky, Ph.D.

Co-Major Professor

John E. Reynolds, III, Ph.D.

Committee Member

Earl D. McCoy, Ph.D.


Habitat selection, Thermoregulation, Temperature, Foraging, Activity Patterns, Human Disturbance


Investigating alternate winter refuges for Florida manatees is increasingly important

as sustained warm-water discharges from industrial and some natural sites becomes more

uncertain. This study examined habitat features of possible importance to manatees by

comparing a winter refuge in Charlotte Harbor, FL (the Matlacha Isles canal system) to

two nearby, seemingly similar sites that are not frequented by manatees during winter.

Water temperature, salinity, boat traffic, canal depth, and tidal flushing were assessed at

these sites. Additionally, this study examined when and how manatees use the Matlacha

Isles refuge by documenting movements, habitat use, and behaviors of manatees during

the winters of 1999/2000 through 2001/2002. Water temperatures had a profound

influence on manatee selection of Matlacha Isles over the two comparison canal systems.

Matlacha Isles did not experience the sudden drops in water temperature following cold

fronts, extreme low temperatures, or long periods of temperatures below manatees’

reported thermal tolerance of 18-20

oC that were recorded in Matlacha Pass (ambient) and

the two comparison canal systems. Heat retention within Matlacha Isles may be

associated with greater water depth and lower tidal flushing. Salinity and boat traffic did

not seem to influence site selection by manatees. During moderately cold weather,

manatees occupying Matlacha Isles forage at night in nearby Matlacha Pass and return

early in the morning to Matlacha Isles, where they primarily rest all day. Neither tidal

state nor boat traffic levels affected manatee travel patterns into or out of Matlacha Isles.

Manatees may passively thermoregulate in the warmer waters of Matlacha Isles during

the day (when they are inactive) and sustain their body temperatures at night through the

heat generated during traveling to feeding sites and during ingestion (chewing) and

digestion. During extreme or prolonged cold weather, Matlacha Isles provides

inadequate warmth for manatees; during such times, most of them travel to a power plant

on the Orange River, approximately 50 kilometers away. Findings from this study may

inform resource managers as they consider attributes manatees find desirable or

necessary in winter. Such information will help managers create new or enhance existing

winter refuges to protect manatees.