by Gary Samson
How Now, Sea Cow?
Hinchinbrook Island, located off the coast of Australia, is a popular vacation destination for hikers and divers. The largest island national park in the world, it is surrounded by clear, warm waters that are heavily populated by dolphins, brightly--colored fish and dugongs--lots of dugongs.
Dugongs are one of four living types of sea cow, with the other three being manatee species found in the Atlantic region. These huge sea mammals--distant relatives of the elephant--are not particularly swift, either in the water or in their mental processes, but they're peaceful. Vegetarians, they pose no threat to other animals or their human visitors, and they survive on a diet of seagrass.
Though dugongs seem numerous in Australia's waters, scientists have become concerned about the species' survival. Dugongs reproduce slowly; females have only one calf at a time and do not begin breeding until they are at least 10 years old. A full-grown dugong has few natural predators, but calves are prey to crocodiles, sharks and killer whales. And all dugongs are imperiled by human activities in their waters. For years, they have fallen victim to collisions with small boats or entanglements in fishing nets. More recently, they have been threatened by a new hazard: the shark nets installed to protect swimmers at Australia's beaches.
It was this problem that drew UNH professor Ken Baldwin '77G to Hutchinbrook last fall. Baldwin, a mechanical engineering professor and director of the Center for Ocean Engineering, visited the island at the request of Amanda Hodgson, a researcher from James Cook University in Brisbane, Australia. Hodgson wanted to find out whether acoustic pingers--a warning device for sea mammals--would keep dugongs away from Australia's nets. Baldwin is a pinger expert, having worked with the devices for more than a decade in the Gulf of Maine and off the coast of Argentina.
Would pingers work in very different conditions in Australia? There was only one way to find out. "To understand whether pingers would be effective, we needed to understand how the technology works in the dugongs' environment and how the dugongs respond to it," Baldwin says. "The first step was to find out how the sound of the pingers travels in their environment."
Dugongs live in muddy bays on Australia's coast and also in areas with flat, sandy bottoms. "Our goal," Baldwin explains, "was to do a comparison of the sound propagation in the muddy-- and the sandy--bottomed areas, since sound will travel very differently in diverse environments."
Working in humid, 90-plus-degree weather, Baldwin, Hodgson and Greg Stone, director of conservation at the New England Aquarium, went out in a research boat each day, running experiments and collecting data. Despite the difficulty of working in the heat and rolling waves, Baldwin enjoyed getting close to the placid sea cows. "The dugongs have no fear," he says. "They swam right up to the boat. One Sunday morning, we had almost 80 swimming all around us."
Researchers expect that the sound from the pingers will travel less far in the muddy areas. Once the data is collected, Hodgson will know at what frequency pingers must be set to have the maximum effect for dugongs in the areas being studied, and her research on the dugongs' response will continue.
Baldwin's work with pingers began several years ago and several thousand miles away. It was the early 1990s, and New England fishermen had a problem. Hundreds of harbor porpoises were getting caught each year in the 300-foot-long gill nets used to fish the ocean floor in the Gulf of Maine. Once they became entangled, the harbor porpoises usually drowned.
These entanglements were damaging the nets and costing fishermen time and money, and the gill net casualties placed the harbor porpoise on the protected species list. Since the porpoises don't breed until they are six or seven years of age and then produce only one calf each year, the large number lost to nets threatened to drive them to extinction. It was a problem shared by fishermen and environmentalists--two groups not known for working together.
But they did work together. Fishermen, environmentalists and scientists began a series of meetings to look for solutions. One possibility was to use pingers as acoustic markers to warn harbor porpoises away from the nets. This tactic had already been used successfully to prevent whale entanglements in cod nets off the coast of Newfoundland. In 1994, the National Fish and Wildlife Foundation funded a field experiment to determine whether pingers would work with porpoises. Scott Kraus, a marine mammal specialist at the New England Aquarium, was the principal investigator on the project, and Baldwin was one of the associate investigators.
Fifteen Maine and New Hampshire fishing vessels participated in the experiment. It was a double-blind study, using active pingers on some nets and dummies on others. The pingers emitted a broadband signal of 10 kHz, repeated every four seconds. The intent was not to frighten the porpoises, but simply to make them aware of the nets so they could avoid them.
To this day, nobody understands exactly why the pingers work, but they do. That initial experiment was an overwhelming success. During the two-month study, only two porpoises were caught in the nets with active pingers, while 25 were caught in the nets with dummies. Today, many fishermen voluntarily use pingers to protect both their livelihood and the harbor porpoises.
Scientists and fishermen have also found wider applications for pingers. In recent years, they have been used on cod and hake nets in the United Kingdom. Two years ago, UNH graduate student Laura Cavagnaro '99G traveled to New Zealand to find out if pingers would work with Hector's dolphin, an endangered species. Last year, Baldwin spent two weeks in Argentina, where researchers from the Museum of Natural History in Buenos Aires are testing pingers for their commercial and subsistence fishing industries to deter and protect LaPlata dolphins.
And now pingers show promise of protecting Australia's dugongs. "If you spend some time around these creatures, you start to gain a different appreciation for their existence, and you realize what they have to deal with to survive," Baldwin says. "They were here first, and it's our responsibility to make amends and make it possible for us to use the same waters."
--Danielle Mostollerblog comments powered by Disqus
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