In a new effort to reduce the number of collisions between manatees and watercraft, scientists from three organizations have embarked on a project that will meld technology with marine mammal bioacoustics research.
Researchers with Scripps Institution of Oceanography at the University of California, San Diego, the Hubbs-SeaWorld Research Institute, and SeaWorld San Diego and Orlando will conduct investigations in San Diego and Florida in a project designed to develop new "manatee finder" sonar-based technology to reduce manatee deaths related to boat collisions. Manatees, which can span up to 14 feet long and weigh more than 3,000 pounds, are typically found in shallow coastal waters and estuaries.
According to the Florida Fish and Wildlife Conservation Commission, 305 of the endangered Florida manatees died off state waters in 2002. Thirty-one percent of those deaths, according to the commission, were watercraft-related, representing the highest number on record and a continuation of an increase in such deaths in recent years.
"Our idea is to have an acoustic system working on a platform that would function as a type of scanning sonar," said Jules Jaffe, Research Oceanographer at Scripps Institution of Oceanography and one of the lead scientists in the project. "You can imagine, for instance, the way certain animals use echolocation to find a target or source. In this case we would design the echolocating system to find the manatees and tell boaters they are there."
According to the project's investigators, boaters and manatees can successfully avoid collisions by locating each other, determining an effective course of action, and reacting appropriately. The responsibility typically falls to the manatee to react appropriately. But animal-vehicle collisions often occur even when animals can detect vehicles because they choose poor strategies for avoiding them. Although some scientists believe that manatees fail to detect or localize oncoming boats effectively, observations of responses to boats have not confirmed this idea. In some cases, manatees have swum into deeper water when they detect boats, the most hazardous strategy they could adopt. It is possible that instinctive predator-avoidance strategies are affecting their decisions. In addition, rapidly moving boats simply leave manatees with no time to implement any kind of avoidance strategy.
"It's easy to see that manatees would get hit when they couldn't get out of the way of a fast-moving vehicle. Even humans get hit that way sometimes. Because they hear boats all the time, they may also get hit when they don't pay appropriate attention to oncoming boats," said Ann Bowles, a co-investigator in the project and a Senior Research Biologist at the Hubbs-SeaWorld Research Institute. "We believe these psychological factors are at least as important as problems in detection and localization. Because of that, manatee-boat collisions will be best avoided by giving the boater the power to react appropriately, even when the manatee doesn't."
Also called "sea cows" because they are known to graze on marine grasses and other water plants six to eight hours a day, adult manatees typically have light to dark gray rounded bodies that span eight to 14 feet and can weigh from 440 to more than 3,000 pounds. Manatees usually stay submerged for about two minutes before surfacing to breathe air. While typically very vocal underwater, they tend to remain silent in situations of perceived danger.
"This is an opportunity to use science and technology to solve a problem facing both manatees and boaters," said Bowles.
Along with Bowles's expertise in marine mammal acoustics, research oceanographer Jaffe will lead the bioacoustic engineering aspect of the project.
Jaffe will test and develop a sonar system capable of acoustically sensing the marine mammals beginning with experiments in SeaWorld San Diego's Manatee Rescue attraction. The 215,000-gallon pool will function as a "laboratory" for the project to test the low sound levels required to detect the manatees.
"We need to figure out how reflective (to sound) the animal is, but we also have to look at their environment and investigate how reflective that is," said Jaffe. "The animal presents the signal and the environment around them is the noise we have to filter out. We will look at the animals at SeaWorld in a very controlled environment and then again in Florida in their natural environment."
The team envisions a buoy platform outfitted with a detection system that will flash a signal to oncoming boaters, alerting them that manatees have been detected in the area. The sonar that will be used has a frequency of 170 kilohertz and is considered safe for the animals. It will be operated at a level of 180 decibels (referenced to one micropascal) or lower, which is lower than that of most fish-finding sonars, and the manatees will not be able to hear the signal.
The project is funded by the Florida Fish and Wildlife Conservation Commission: Florida Marine Research Institute; Busch Entertainment Corporation, the Hubbs-SeaWorld Society, and is being done under the appropriate federal endangered species permits.
Facts about the manatee finder project
(1) The scientists are operating under a U.S. Fish and Wildlife Service permit, which specifies the decibel levels they may use and the exposure time.
(2) Dr. Ann Bowles sits on the Acoustic Criteria Panel, which is setting exposure limits for marine mammals under the auspices of the National Marine Fisheries Service.
(3) The scientists are working below conservative safety limits.
(4) The study subjects will not be able to hear the sonar test signals used by Dr. Jules Jaffe, which are at 170 kHz, more than three times higher than the upper limit of hearing for manatees at 30-36 kHz.
(5) The scientists will conduct a series of tests with a 16 kHz sound that manatees can hear to determine what, if any, behaviors occur at levels below the maximum. This signal will be stepped up gradually in case there is a threshold of discomfort. If there is, the scientists will alter the experiment accordingly.
Related Video: Ann Bowles on the project and manatees