During the past meetings, the Manatee Technical Advisory Council (MTAC) has focused on vessel-related manatee mortality and management strategies for reducing collisions between manatees and watercraft. MTAC’s activities included a workshop on acoustic research and technology, with presentations on the work of Edward Gerstein and Joseph Blue, who have developed a sound-emitting device that they believe could be placed on boats and improve manatees’ ability to hear and avoid the vessels. This idea has received wide attention from the news media and those interested in boating and manatee protection, and was also the subject of a proposal to the U.S. Fish and Wildlife Service for a permit to test the device on wild manatees in a natural setting.
Staff of the Florida Fish and Wildlife Conservation Commission (FWCC) has requested the Council to provide specific guidance related to acoustic technology as a possible tool for manatee protection. FWCC staff have stated that acoustic technology, such as the sound-emitting device, may represent an opportunity for manatee protection that should not be overlooked. MTAC has not reviewed the specific proposal or the regulatory issues associated with the permit application for testing the Gerstein-Blue device, and therefore has not offered specific comments on its merits. Rather than reacting to a particular proposal or design, MTAC has pursued a broader, more proactive approach of identifying management priorities and science needs necessary for developing and assessing acoustic technology generally.
Based upon the material presented at previous meetings, MTAC concluded that experiments with captive animals and preliminary tests of boat sounds demonstrate that manatees can hear sounds in the frequency range that boats make. However, their response to boats in the environment is variable. The animals sometimes dive or appear to move toward deeper water when approached by vessels, but have also been observed to turn or move toward an approaching boat. The manatees’ response appears to be affected not only by hearing ability, but also by acoustical properties of the environment and behavioral factors, which are less well understood. Thus, while it is tempting to hope that a specially-designed sound-maker would alert manatees sooner of an approaching vessel, it is not at all clear that wild animals in a natural setting have the cognitive ability to recognize a particular sound as a danger or determine how to escape. It is not appropriate to ascribe human learning abilities and reactions to manatee behavior. If the sound is inherently aversive, it may be considered harmful to manatees and other animals. Also, in the long-term, animals may become habituated to sounds typically present in their environment, which may affect their response to any familiar noise.
MTAC views technological advances as tools which may complement, rather than replace, traditional management strategies, such as planning, regulation, enforcement, and education. MTAC supports continued evaluation of acoustic and other technology for applications in various manatee protection strategies. However, a fundamental understanding of the acoustic properties of boats, sound and its propagation in the natural environment, as well as manatee hearing, behavior and cognitive ability must be established in order to effectively evaluate any technological approach involving potential use of sound for manatee protection. These avenues of applied research provide a framework of priorities for further study. Additionally, prior to testing any technology, some type of objective “success criteria” or performance measures should be established and agreed upon by managers in order to quantify benefits or impacts arising from use of the device:
Specific issues or hypotheses requiring additional applied scientific research are listed below:
Manatee hearing and behavior
More experimental research is needed to determine the minimum audible angle, or directional sensitivity of manatee hearing.
Age and history of exposure to noise may affect manatee hearing. Anatomical studies during necropsy may provide some insight into this area.
Manatees may not have the cognitive ability to recognize a sound as a warning or determine how to escape.
Manatees may hear boats adequately, but may not react because they have become habituated to them as “background” noise.
More basic understanding of manatee behavior is needed to assess response and establish “success criteria” for evaluating whether or not a sound-emitter would change the likelihood of manatee-vessel collisions.
Acoustic properties and sound transmission
Basic descriptive information on the acoustic environment experienced by manatees in natural settings is needed. This would include data on sounds produced by various vessels and amounts of traffic, “background” sounds, and typical acoustic conditions particularly in areas of high manatee mortality.
Bubbles and turbulence, such as that created by prop wash, may affect sound transmission when multiple boats are present. The risks to manatees may be increased in the presence of multiple boats following each other.
Seagrass or other aquatic vegetation may affect sound propagation.
Banks, channels, and configuration of water bodies may affect sound propagation or create acoustic “shadows.”
High mortality areas may be associated with certain physical settings that suggest barriers to sound transmission.
Background noises, such as rainstorms, may affect manatee ability to distinguish boat sounds.
Management considerations related to sound-producing devices
Using a noise to frighten or engender a reaction in manatees may create an adverse impact, or be perceived as an impact, rather than a benefit. Of particular concern are sensitive behaviors that may be disrupted by additional noises, such as cow-calf interactions.
Cumulative effect of thousands of underwater sound-producing devices on manatees and other animals must be considered. A federal EA or EIS may be required in order to allow manatee protection sound makers.
A sound-omitting device to “warn” manatees may affect the way that boaters operate.
Members of the Manatee Technical Advisory Council are appointed by the Governor of Florida to provide recommendations on manatee-related issues.
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