In recent years, there has been concern that man-made noise may be a cause of stress for dolphins, whales and other marine mammals, but the results of a five-year study show that noise pollution – especially noise generated by seismic airguns during geophysical exploration for oil and gas – seems to have minimal effect on endangered sperm whales in the Gulf of Mexico, say researchers from Texas A&M University who led the project and released their 323-page report today at the Houston Museum of Natural Science.
The multi-year $9 million study, the largest of its type ever undertaken and formally titled Sperm Whale Seismic Study in the Gulf of Mexico, was conducted by the Minerals Management Service and featured cooperation with the Office of Naval Research, the National Science Foundation and the National Fish and Wildlife Foundation. The project brought together researchers from eight universities, but it was managed overall by Texas A&M's Department of Oceanography, with research scientist Ann Jochens and professor Doug Biggs serving as principal investigators.
"The bottom line is that airgun noise from seismic surveys that are thousands of yards distant does not drive away sperm whales living in the Gulf," Biggs explains.
"However, some individual whales feeding at depth reduced the rate at which they searched acoustically for their prey when scientists carried out controlled exposure experiments by bringing seismic surveys close by the whales. As a result, the oil and gas industry has agreed to a best-practice attitude that seismic surveys should shut down temporarily when towed airguns come within one-third of a mile of whales or groups of whales in the Gulf."
Though not often seen, sperm whales are regular visitors to and residents in the Gulf of Mexico. They are the largest of all toothed whales and can reach lengths of 60 feet or more and live 60 years or longer. Their primary diet is squid and fish and they have been known to dive as deep as 7,000 feet. Humans no longer hunt them for their oil, but the whale in Herman Melville's classic novel Moby Dick was a sperm whale.
Sperm whales are not often seen because they prefer to stay in the deep waters of the Gulf, usually in depths of 3,000 feet or more and at least 150 miles offshore, Biggs says.
"Sperm whales go to where their food source is, and that means very deep water. So folks that do see them are marine mammal observers who ride the seismic survey vessels and the workers on the big oil and gas rigs, and even that does not happen often," Biggs adds.
The primary concern facing the scientific research group was noise – there's more of it in the world's oceans than you might think. A study by the Scripps Institution of Oceanography shows that the world's oceans are 10 times noisier since the 1960s, and at any one time, there are as many as 30,000 ships circling the globe.
Biggs says that over the course of five summers, 98 sperm whales were tagged with devices that relayed back critical data such as measurements about sound levels and behavioral aspects of whales, including tracking their movements. Of particular concern was the effect that loud low-frequency noises, such as those created by seismic activity, might have on sperm whales in the area.
Oil and gas companies prospect for subsea reservoirs by firing air guns during their seismic work, which government regulators thought might negatively affect sperm whale behavior. Also, the sheer volume of work being done in the Gulf was another concern: The Gulf of Mexico accounts for almost 70 percent of the oil and gas extracted from U.S. waters and there are thousands of oil and gas platforms in the region.
But the study found no unusual effects of controlled exposure to seismic exploration on the swimming and diving behavior by sperm whales in the Gulf, and also revealed a wealth of data about sperm whale biology and habitat.
"We now know that the sperm whales in the Gulf appear to be their own distinct stock – they show genetic and social differences from other sperm whales around the world," Biggs says.
"There are believed to be about 500 to 1,500 sperm whales that reside in the Gulf. Most of these are family groups of females and maturing young. When one family group socializes with another family group in the Gulf, they make very distinct sounds. Even though the family groups are visited by males that come into the Gulf from other oceans, their 'clicking' sounds, called codas, the Gulf sperm whales make appear to be different from most others made by sperm whale groups in other parts of the world.
"The five-year study has greatly contributed to our knowledge of sperm whales, especially those found in the Gulf of Mexico. It's also raised new questions we need to know more about, such as their feeding and breeding patterns. There's still a lot we don't know about these huge creatures."
Keith Randall | EurekAlert!
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