Anyone who lives near a busy highway can sympathize with the North Atlantic right whale: Research released Wednesday shows the leviathans off New England’s coast are subject to such a constant undersea din it is difficult for them to hear each other most of the time.
It is a hazard that could be hindering the critically endangered species’ ability to navigate, avoid predators, and care for calves.
Global trade and the cruise industry have brought more, larger, and noisier ships to the region, resulting in the whales losing about two-thirds of their ability to communicate with each other compared with about 50 years ago, the National Oceanic and Atmospheric Administration-led paper found. The estimated 450 right whales left in the world are believed to use their ethereal moans, whoops, and whistles to find food and mates, and to avoid peril in the sea.
“There is this overall hum they have to deal with, and it’s increased over time,’’ said Leila Hatch, NOAA’s Stellwagen Bank National Marine Sanctuary marine ecologist and lead author of the paper that appears in the journal Conservation Biology.
While authors of the study said they can’t tease out how much the noise is affecting whales compared to myriad other problems facing the animals, they said it is probably significant. They estimated background noise levels have risen about 10 decibels off Boston over the last half-century. Such an increase, scientists say, represents a dramatic change.
These “whales rely on their ability to hear far more than their ability to see,’’ Hatch said. “Chronic noise is likely reducing the opportunities to gather and share vital information.”
The study may prove useful as the International Maritime Organization works on guidelines to reduce noise from ships’ engines and propellers and other machinery, so that less noise is transferred to the water and whales.
The researchers spent three years using submerged acoustic recorders in and around Stellwagen Bank to measure real-time locations, levels, and types of sound from ships, whales, and the ocean overall. In April 2008 alone — the peak of right whale feeding season off Massachusetts — scientists documented more than 22,000 right whale calls.
The group, including researchers from Cornell University, NOAA’s Northeast Fisheries Science Center, and Marine Acoustics Inc., an environmental consulting group in Arlington, Va., also estimated how underwater sound had changed over time by comparing a patchwork of available historical data from similar water bodies and linking it back to Boston.
While Jacques Cousteau dubbed the submerged depths “The Silent World,” the oceans in their natural state are, in fact, filled with squeaking dolphins, grunting fish, and even an undersea roar from occasional storm winds. But ships, sonar, oil exploration, and other water traffic are also drowning out conversations among marine mammals that rely on their super-sensitive hearing to navigate and communicate.
Sound, especially the kind of low frequencies large whales use, travels five times faster under water than on land and can be carried across vast ocean channels. Whale pods often communicate across hundreds, if not thousands, of miles.
Just as a construction blast bothers nearby humans, shorts bursts of sound perturb marine animals, according to a growing body of evidence compiled by scientists. For example, dolphins have refused to perform tasks if noise is too loud, and noise has been suggested as the cause of a handful of beached whale cases.
The study, while measuring peaks of sound when ships passed nearby, focused mostly on background noise that paper coauthor Christopher Clark of Cornell University dubs “acoustic smog.” Much the way smog that can obscure a view from Provincetown to Plymouth, he said, the background noise obscures whales’ ability to communicate over large distances.
Scientists are particularly concerned about the North Atlantic right whale, so named because it was the “right” whale to kill for oil because it floated when dead. The dark-colored animals have never made a comeback after being hunted nearly to extinction in the 1700s.
Many of the creatures get tangled in fishing gear, but others are struck by ships. There have been ongoing efforts by environmentalists, government, and industry to move shipping lanes away from Boston and require slower vessels near feeding whales. There is even an iPad and iPhone app that warns mariners along the US East Coast when they enter areas of high risk of collision with the right whales.
Enormous numbers of vessels come in and out of Boston ports, or steam right by on their way to other locations. But scientists, and statistics, point to more, larger, and likely louder, ships inhabiting waters off our coast. While statistics going back 50 years were unavailable, 62 cruise ships and 287 vessels carrying salt, scrap metal, asphalt, auto, oil, and gas steamed into the port of Boston in 1998, according to Massport. In 2011, there were 107 cruise ships and 315 other large vessels.
“Basically, the whales off Boston now find themselves living in a world full of our acoustic smog,’’ Clark said.