Vocal behavior of Florida manatees during vessel approaches.

Abstract

Florida manatees (Trichechus manatus latirostris) spend much of their lives in an “urbanized” ocean with high levels of vessel traffic being common during much of the year. To explore the detailed acoustic and motor behavior of manatees during vessel approaches, digital archival tags were attached to animals in the waters of southwest Florida in 2007 and 2008. These tags record sounds produced by the manatee and other sounds in the environment up to 32 kHz as well as sampling a suite of behavioral and environmental sensors at 50 Hz. The vocal behavior of manatees before, during, and after vessel approaches was investigated. Vocalizations were assigned to the tagged manatee by the higher amplitude and the presence of higher frequency harmonics compared to signals produced by nearby animals. Dolphins have been found to increase their vocalization rate at the onset of vessel approaches, and we have numerous vessel approaches to 20 individuals to evaluate manatee vocal behavior in these contexts. We will present results from single as well as multiple boat approaches and compare these vocal rates to periods without boats. In addition to reporting vocalization rates during vessel approaches, we are investigating the types of signals used by manatees in these situations.