WASHINGTON D.C. - Whale songs can travel thousands of miles, but an increasingly noisy ocean is drastically cutting down their ability to communicate, shows new research that suggests ever-increasing noise could impede the beasts' ability to navigate and find mates.

Whales sing at a low frequency, at the very bottom of the range of human hearing. To hear the whales, "you have to broaden your listening range," said Christopher Clark of Cornell University, adding that, "their voices are beautifully adapted for long range transmission. They are acoustically extremely prolific."

By singing at low frequencies, whales are able to communicate across oceans - it's how they keep track of their pod and alert friends of a good place to eat.

Using an underwater sound surveillance system more typically employed for tracking submarines, Clark and his colleagues zero in on specific whale songs and even track whales based on where the songs originate from.

Puerto Rico to Newfoundland

"If we went to the shelf-edge of Puerto Rico we could hear blue whales off Newfoundland 1,600 miles away," Clark said here this weekend at the annual meeting of the American Association for the Advancement of Science.

But Clark and other scientists are concerned that the growing "acoustic smog" in the world's oceans, and particularly the waters near popular migration and feeding routes, is interfering with whales' ability to communicate with songs.

"A blue whale, which lives 100 years, that was born in 1940, today has had his acoustic bubble shrunken from 1,000 miles to 100 miles because of noise pollution," said Clark. "The noise pollution is estimated to be at the industrial noise level where OSHA would require us to wear headphones."

Noise pollution is doubling every decade in an urbanized marine environment, Clark claims, mostly due to shipping traffic.

"If females can no longer hear the singing males through the smog, they lose breeding opportunities and choices," he said.

Clark suggested that the shipping industry overhaul their ships and begin using quieter propellers. A more economically feasible fix might be to reroute shipping traffic so that it no longer passed through popular whale habitats, he said.

Spaced out

Very little is known about whale communication. Clark and colleagues, U.S. Navy acoustics experts Chuck Gagnon and Paula Loveday, have been been using the underwater microphones of the Sound Surveillance System (SOSUS) system to track blue, fin, humpback and minke whales. They find that the process of communication among whales is a broader concept, in both time and space, than humans have conceptualized.

"There is a time delay in the water, and the response times for their communication are not the same as ours," Clark said. "Suddenly you realize that their behavior is defined not by my scale, or any other whale researcher's scale, but by a whale's sense of scale -- ocean-basin sized."

Whale sonar is also important for navigation.

"Whales will aim directly at a seamount that is 300 miles away, then once they reach it, change course and head to a new feature," Clark said. "It is as if they are slaloming from one geographic feature to the next. They must have acoustic memories analogous to our visual memories."

In separate research presented this weekend, DNA analysis of whales shows their populations grew steadily through history, with drastic declines recently.

"Whales have shown remarkable resilience to cataclysmic events -- until the last one -- which is us," said Steve Palumbi of Stanford's Hopkins Marine Station. "Ice ages, sea level change and even loss of local food sources did not interrupt their lives. Living in a fluid environment they could move to new areas of productivity and find food even as the climate around them changed."

LiveScience's Robert Roy Britt contributed to this report.