Manatee response to environmental noise

Jennifer L Miksis-Olds, University of Rhode Island


The most pressing concerns associated with conservation of the endangered Florida manatee (Trichechus manatus latirostris) include habitat alteration and mortality caused by humans. Whereas considerable research has focused on manatee mortality associated with watercraft collisions, little attention has been paid to the impacts of noise created by watercraft. Potential effects of environmental noise on the habitat selection, distribution, and behavior of manatees are the foci of this dissertation, the primary goal of which was to understand and predict manatee behavior patterns as a function of environmental noise levels in the Sarasota Bay area. Manatee behavior was examined in terms of: (1) habitat selection and distribution, (2) activity budget, (3) vocalization usage, and (4) short-term response to playbacks of approaching watercraft. ^ The initial phase of the study used acoustic modeling and monitoring to relate transmission loss and noise levels in specific manatee habitats to animal distribution. High-use grassbeds were quieter than low-use grassbeds of equal species composition and density, indicating a correlation between manatee distribution and environmental noise levels. In the morning the presence of boats and their associated noise may also play a dominant role in the timing of grassbed usage. ^ The degree to which manatees alter their patterns of behavior and vocalization under different environmental noise levels was investigated in the observation phase of the study. Results indicated that elevated environmental noise levels correlate with the overall activity budget of this species. More time was spent in the directed, goal-oriented behaviors of feeding and traveling whereas less time was spent milling when noise levels were highest. When noise levels were elevated, manatees increased their call duration during feeding and milling behaviors, suggesting that ambient noise levels have a detectable effect on manatee communication and that manatees modify their vocalizations as a function of noise. ^ Manatee response to the playback of an approaching boat was assessed in the final phase of the study. Results indicated that manatees respond differentially to different categories of boat noise used in the playback study. The most pronounced responses to boat noise playbacks, relative to the controls, were elicited by personal watercraft. ^

Subject Area

Biology, Ecology|Biology, Oceanography|Biology, Zoology

Recommended Citation

Jennifer L Miksis-Olds, "Manatee response to environmental noise" (2006). Dissertations and Master's Theses (Campus Access). Paper AAI3225323.