Sonar systems—first developed by the U. These sound waves can travel for hundreds of miles under water, and can retain an intensity of decibels as far as miles from their source. These rolling walls of noise are no doubt too much for some marine wildlife.
While little is known about any direct physiological effects of sonar waves on marine species, evidence shows that whales will swim hundreds of miles, rapidly change their depth sometime leading to bleeding from the eyes and ears , and even beach themselves to get away from the sounds of sonar.
Other sad examples around the coast of the U. In , NRDC spearheaded a successful lawsuit against the Navy to restrict the use of low-frequency sonar off the coast of California. In filing their brief, the groups cited Navy documents which estimated that such testing would kill some , marine mammals and cause permanent injury to more than whales, not to mention temporary deafness for at least 8, others. Environmental groups are still fighting the battle against the sonar, lobbying the government to curtail testing, at least during peacetime, or to at least ramp up testing gradually to give marine wildlife a better chance to flee affected areas.
Box , Westport, CT ; earthtalk emagazine. They found that a sonar ban introduced there in had been effective in reducing whale strandings and called for more sites to be established to prevent further deaths, including in the Mediterranean, where beaked whales are listed as vulnerable. Beaked whales regularly dive deeper than one kilometre for longer than one hour, but when exposed to sonar they may dive for more than two hours to a depth of nearly three kilometres.
Peter Tyack, professor of marine animal biology at the University of St Andrews, said exposure to sonar "pushes some whales over the edge — some lose their ability to manage gases under pressure, causing gas bubbles that can injure or kill, and some strand on the beach and die". We need better monitoring of sound in the ocean coupled with policies that reduce exposure of vulnerable species to tolerable limits.
Sonar was developed in the s to detect submarines — and mass strandings of beaked whales were rare before this point. But between and there were more than mass strandings reported and the number of species affected by the pulses increased. In one case shortly before the Canary Islands ban, fourteen whales beached during a Nato drill involving sonar. Strandings in , , , and also coincided with naval exercises. As recently as last summer five whales died along the Irish coast in a suspected sonar-related incident.
The latest study's findings suggested that animals which had not become accustomed to the sonar sounds were even more at risk than those which experienced them frequently. Sarah Dolman, policy manager at Whale and Dolphin Conservation who was not involved in the study, said the latest research confirmed that beaked whales were "very vulnerable" to military exercises.
For over a decade, the Navy has been trying to convince the courts that they can use an ultra-loud sonar array in a way that is safe for marine life. The ruling came down to a Navy-friendly interpretation of the National Marine Protection Act, which prohibits any US citizen, agency, or organization from harming creatures like whales, dolphins, and seals.
During the s, however, the Soviet Union was developing quieter submarines. At the same time, the ocean itself was getting noisier from activities like oil drilling and marine shipping. So the Navy started working on a special long-range sonar tool. But sonar it is. The system deploys from the aft ends of special sub-hunting surface ships. The problem is those frequencies—from around to hz—also happen to be the sweet spot for a lot of marine life. Whales, dolphins, and porpoises use sound to find food, meet mates, avoid predators, maintain social groups, or simply navigate the wide seas.
0コメント