Whales, Dolphins and Ocean Noise
Latest Protests Highlight Effects on Marine Mammals
Whales and dolphins rely heavily on echolocation and vocalization to find food and communicate. Boat traffic, sonar, oil and gas exploration and navy exercises interfere.
Protests in Hawaii over planned naval exercises near the Hawaiian Islands Humpback Whale National Marine Sanctuary address just one aspect of the ocean noise problem. In the wake of multiple mass strandings of varied species of whales, the link between naval exercises and these events has become a very controversial topic. And there are other sources of noise that are also affecting marine mammals.
Boats, Oil and Gas Exploration, and Industry
Engine noise from large ships and even recreational boats causes dolphins and whales to alter their behaviour. Oil and gas exploration, construction, power plants and factories all contribute to the problem.
Whales and dolphins exist in a world of underwater sound. Most people are familiar with the clicks and whistles of dolphins and the eerie sounds of humpback whale songs. Some of these sounds can carry up to a mile away and are a vital part of cetacean communication. In addition, dolphins and toothed whales use echolocation to find schooling fish.
Most of cetacean hearing and vocalization occurs in the 10Hz to 200kHz range, depending on species. Construction, dredging, powerplant and factory noise tends to be in the 10Hz to 1kHz range. And shipping and navigation noise runs between 10kHz and 220kHz. That means that much of the human generated noise has serious potential to interfere with dolphin and whale activities and communication. These marine mammals will avoid that noise if they can. That avoidance costs them energetically. To make things worse, mothers with calves appear to be the most sensitive to boat noise of any type and the highest level of nutritional stress occurs in nursing females.
Naval Exercises and Mass Strandings
The mass stranding situation has become quite dramatic, with occurrences in the Bahamas(2000), the Canary Islands (2002, 2004), Washington state (2003), Alaska (2004), Hawaii (2004) and North Carolina (2005), each associated with the timing of naval exercises. Not all cases have been proven but the evidence is mounting as more organizations are aware of the problem. The types of injuries, haemorrhaging in the brains and ears suggest compression/decompression damage. Interestingly, despite claiming little or no fault in the mass strandings, the navy has applied for exemption from the US Marine Mammal Protection Act, which prohibits harassing, injuring or killing these animals.
Awareness of critical habitat for whales and dolphins, such as the humpback nursery in the National Marine Sanctuary, can be used to encourage moving the naval exercises away from these important calving or feeding grounds. Monitoring areas of known naval activity will detect mass strandings, even in remote locations, which can then be recorded and post mortem exams performed on the animals involved.
Sources:
Sound Effects, Bree Ullman, (The Honolulu Weekly, Wednesday 25 April 2007)
Ocean Noise and Marine Mammals, Committee on Potential Impacts of Ambient Noise in the Ocean on Marine Mammals, National Research Council
The Natural History of Whales and Dolphins, Peter G H Evans (Christopher Helm, 1987)
