Mast Foraging by West Indian Manatees (Trichechus manatus)

O'Shea, Thomas

Sirenians have been reported to eat a variety of aquatic and semi-aquatic plants (see review by Best, 1981), but no published accounts of foraging on mast are available. I observed extensive underwater feeding on live oak (Quercus virginiana) acorns by wild West Indian manatees (Trichechus manatus) at a clear Florida spring during autumn and early winter 1983. Here I describe these observations, and include remarks on the ecological influences of birds and fish on the patterns of underwater acorn availability. Observations were made at Blue Spring Run, Volusia County, Florida, a 650 m long, 20 to 30 m wide artesian spring which flows directly into the St. Johns River at a point approximately 240 km from the Atlantic. Manatees use Blue Spring as a thermal refuge during cool winter weather. They spend the warm seasons in the St. Johns River and forage nearly exclusively in the river during all seasons including winter (Bengtson, 1981; Powell and Waldron, 1981). Blue Spring maintains a constant water temperature of 22.5"C, and manatees take refuge there each winter beginning in November or December, when the river temperature drops below 20"C (Bengtson, 1981; Powell and Waldron, 1981). During winter 1983-84 a total of 43 individually identifiable manatees used Blue Spring.

Mast Foraging by West Indian Manatees (Trichechus manatus)

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