Effects of temperature on abundance and distribution of the West Indian manatee (trichechus manatus) at three power plants along the east coast of Florida

Gutfran, Jean Marie
Jon Atwood, PhD
Department of Environmental Studies
I studied manatee abundance and distribution during the 2002-2003 winter season at three power plants on the east coast of Florida: Vero Beach Municipal Power plant, H.D. King Power plant, and Riviera Beach Florida Power and Light plant. Ground-based surveys from fixed viewing locations were used to observe manatee numbers and behavior in the discharge canals. Ambient air and water temperatures were also examined to evaluate the extent to which these variables prompted manatees to seek out warm water. Manatees used all three sites as warm water refuges. Southward migration by manatees in northeastern Florida causes the Riviera Beach site to have the greatest counts during the coldest months of the season. Vero Beach and Fort Pierce, while supporting smaller numbers than Riviera Beach, are important midway stopping points during migratory travel. Manatee abundance at Vero Beach and Riviera Beach sites were negatively correlated. No correlation was observed between the Fort Pierce site and the other two locations. Multiple regression analysis showed significant relationships between manatee counts and range (ambient temperature) as well as counts and location (Vero Beach site compared to the combined Riviera Beach and Fort Pierce site). While analysis of 7 previous years of census data from Fort Pierce and 2 from Vero Beach showed no significant change in mean manatee counts over the years analyzed, visual evaluations suggests a decreasing trend. Data from this study reflects the importance of power plants at Riviera Beach, Fort Pierce and Vero Beach as winter habitat for manatees, and suggests that continued monitoring at these locations is warranted.

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