Every year, thousands of whales and dolphins strand themselves on beaches and often die. Scientists think that the whales may strand themselves individually or in groups for a variety of reasons. In recent years, beaked whales, which are not usually known for this behavior, have been beaching themselves with alarming frequency. Are human actions related to this increase?
HYPOTHESIS: Sonar Causes Whale Beachings
The ocean is filled with sounds generated during human activities: shipping, fishing, oil drilling, oceanography research, and military operations. The U.S. Navy, for instance, uses a sonar system to detect submarine movements. The blasts of low frequency sound used by the military are so loud they can travel hundreds of miles at decibel levels equivalent to the sound of jet engines.
In March of 2000, 16 whales beached themselves on the Bahamas within 24 hours of a Naval sonar test. Six died. Kenneth Balcomb heads the Bahamas Marine Mammal Survey research station. Balcomb was aware of several past incidents in which mass strandings occurred around the time of naval maneuvers. It was unknown whether these events were connected. The closeness and timing of the Naval testing in the Bahamas seemed to suggest a sound-related stranding. Balcomb and co-researchers hypothesized that the loud sonar damaged the whales' hearing and in some way led to the beachings.
METHODS: Autopsy Whales and Analyze Tissue
Balcomb quickly removed the heads of two dead whales, froze the 200-pound specimens, and had them flown to the Woods Hole Oceanographic Institute in Massachusetts. There, he and others performed CT scans and microanalysis of inner ear and brain tissues.
Scientists are currently studying why whales are beaching themselves at increasing rates. Members of the Marine Animal Rescue Society are performing an autopsy on this beached whale.
RESULTS: Tissues Show
The whales that were examined all showed similar lesions, including internal bleeding, known as hemorrhaging, in the acoustic regions of the cranium and mandible and in tissues next to airspaces around the ear bones. One specimen that was examined by ultra high-resolution computerized tomography showed a brain hemorrhage. In addition, dissection of this same specimen showed lung hemorrhage and laryn-geal hemorrhage.
CONCLUSION: Evidence Supports Sonar-Induced Tissue Damage and Death
Based on the results of specimen examination, the National Marine Fisheries Service and the Navy came to the same conclusion: the injuries were all consistent with an intense acoustic or pressure event.
In September of 2002, 14 more whales stranded themselves in the Canary Islands following military maneuvers by NATO using sonar. Paul Jepson of the Zoological Society of London and colleagues found that the whales suffered tissue and organ damage similar to that found in the whales beached in the Bahamas.
In June 2003, a federal judge-magistrate in San Francisco ruled that the Navy must limit its plans for low-frequency sonar exercises. The Navy is currently working to establish those limits.
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