Abstract

Approximately 25% (1184) of the 4757 Florida manatee (Trichechus manatus latirostris) deaths recorded during the 25 years between January 1, 1979 and December 31, 2003 represent watercraft-related mortality. The wound patterns generated by collisions with watercraft are often recognizable and therefore are diagnostic of watercraft collision. Watercraft-related injuries occur most frequently to the dorsal aspect of the animal. Lesions may include linear cuts or scrapes that are roughly parallel to the direction of vessel travel and which, if paired, are roughly parallel to each other. These linear wounds and scars are consistent with impact from one or more fixed watercraft projections such as keels, skegs, strakes, plates, tabs, propeller shafts, struts, or rudders. Additionally, linear, crescent, and/or sigmoidal wounds may be generated by propeller blades. These lesions, typically observed as sets of parallel equidistant cuts and scrapes, are roughly perpendicular to the direction of vessel travel. Propeller diameter and pitch, as well as handedness of propeller rotation, can often be determined from wounds and wound patterns. Identification of certain watercraft components can be useful in determining the type of vessel involved in a collision. Such details can later be used in the implementation of management strategies.

Acknowledgments

Thanks to Judy Leiby for improvements to this abstract. This work was supported by the state of Florida's Save the Manatee Trust Fund and by a grant from the U.S. Fish and Wildlife Service.