Gentle Giants in Dark Waters: Using Side-Scan Sonar for Manatee Research

ABSTRACT

Manatees are tropical marine mammals that live in a wide variety of aquatic habitats ranging from coastal marine areas to freshwater lakes and rivers located hundreds of kilometers inland. All manatee species are currently characterized as Vulnerable by the International Union for Conservation of Nature (IUCN), primarily due to anthropogenic causes (i.e. poaching, habitat destruction, pollution, collisions with boats) and all of the environments they live in present challenges to biologists and wildlife managers. Tropical freshwater systems are especially difficult to work in because they are generally tannin-stained or turbid and water clarity is very restricted. Locating manatees and observing their behavior in these environments is extremely difficult and is a major limiting factor in determining population parameters. We summarize the use of sonar technology as an aid to detect and study manatees in these freshwater systems. First, by a summary of what has been attempted before our efforts, followed by presenting the various ways we have used this technology in the past 6 years to 1) detect manatees, 2) characterize manatee habitat in ways that would not be possible otherwise, 3) identify mother-calf pairs, and 4) assist in manatee captures. Finally, we discuss the advantages and limitations of using this technology for manatee conservation and research and present directions in which we believe future work can be directed, such as the determination of manatee abundance via distance sampling surveys using sidescan sonar and the use of one of the latest developments in acoustic technology, dual-frequency identification sonar.