The oceans were once a relatively quiet place. Yet in recent decades, anthropogenic ocean noise levels have risen markedly—doubling every decade for the past 50 years, according to research by scientists at Scripps Whale Acoustic Lab. Today, due to the volume of shipping as well as offshore oil and gas drilling and exploration, the din underwater—where sounds can travel long distances—is constant. In fact, some scientists say virtually no marine environment is now without noise pollution. This finding is startling to scientists who study cetaceans and other marine life, as it is becoming clearer that whales rely heavily on the integrity of their acoustic habitat. If ocean noise continues to increase as a result of human activities, whales may soon have nowhere to go.
Of greatest concern are low-frequency sounds that travel long distances in the ocean. Ship propellers and motors, for instance, produce sound at low frequencies, as does seismic activity. These profound, loud noises reverberate in the deep ocean and can effectively mask or block vital whale communication. In Cape Cod Bay, man-made noise has reduced right whales' acoustic habitat by as much as 80 percent, says Chris Clark, director of Cornell University's Bioacoustics Research Program.
To better understand these underwater acoustics, Clark and his colleagues have developed graphic animations that show the acoustic habitat as experienced by whales. Using data collected by seafloor sound monitors, the scientists can map the locations of whales and measure their sounds, along with anthropogenic sounds. The resulting animations vividly depict how the noise from human activities physically obstructs and reduces whales' habitat, interfering with what Clark calls the animals' "communication space."
The broader aim, says Clark, is to shift the research and mitigation paradigm from using decibel level to using acoustic habitat as a measure of the impact of noise on marine mammals. This would mean considering noise effects from an ecosystem perspective rather than a single-source perspective.
The approach is important for conservation because it will help researchers in efforts to document habitat loss, which has legal ramifications under the Endangered Species Act. For instance, such findings will play into decisions about the location, timing and technology of marine development—including cruise and cargo ship traffic, oil and gas rigs and offshore wind farms (which create high levels of noise during construction and moderate levels when operational).
Overall, the animations will help stewards of ocean life think about underwater sound in three dimensions, says Greg Silber, coordinator of recovery activities for endangered large whales at the National Marine Fisheries Service of the National Oceanic and Atmospheric Administration (NOAA).
For whales, chronic background noise creates conditions like those we'd experience living in a constant fog, says Clark. Certain loud noises are the acoustic equivalent of a blindfold.
That's because marine mammals live in an "acoustic-dominant world," Clark explains, and use sound as their primary means for interpreting their underwater environment. Disruptions create barriers between whales and information they need to know about their habitat. There is growing concern among scientists that anthropogenic noise is having a significant detrimental effect, adding to stress caused by depleted food sources, fishing-gear entanglement, overfishing, pollutants and ship strikes, notes Scripps Institution of Oceanography professor John Hildebrand.
Clark says he has seen whales abandon a location because of noise, sometimes leaving behind a rich food source. This is of particular concern for right whales, a species that remains faithful, year after year, to particular habitats. Changes in feeding influence reproduction, and anything that harms whales' ability to calve ultimately jeopardizes survival.
New data documenting the effects of acoustic habitat degradation on humpback whales, fin whales and acoustically active fish—including haddock and cod—are now being analyzed. The situation appears to be most dire for right whales, particularly in Cape Cod Bay, as their calls are quieter and therefore more vulnerable to disturbance. Among the questions scientists hope to answer with the new observations is how noise pollution affects humpback whales’ feeding calls.
How whales use sound
Sound occurs naturally in the ocean, of course—from waves, wind, precipitation, ice movement and fish, among other sources. But it's the chronic occurrence, intensity and frequency of anthropogenic noise that makes it so disturbing to whales and other sea life. In addition to causing generalized stress, noise may also affect developmental and immune system health, notes Hildebrand.
"We are so pervasive in our impacts in the ocean that there is no place where there [are] no sounds," says Sofie Van Parijs, bioacoustician at NOAA's Northeast Fisheries Science Center. "Anthropogenic noise can interrupt a variety of critical behaviors the animals may be pursuing at the time."
Whales use sound to find and follow prey as well as for back-and-forth communication. Feeding, calf rearing and mating all involve specific calls, and each whale species uses sound distinctively, explains Van Parijs. Different species also have distinct hearing abilities attuned to various frequencies of sound that can span long distances, often several kilometers or more.
Within the lifetime of the whales that Clark has been observing (some of the right whales he studies can live for 70 years), anthropogenic noise has increased dramatically. "When these long-lived species were kids and teens, the world was normal," says Clark. "Now their background noise has gone up by three orders of magnitude."
This disturbance has implications for human activity too. Anthropogenic noise is regulated in marine environments where endangered species—like the right whale—are present; any noise loud enough to result in injury or harassment is prohibited, explains Leila Hatch, a marine ecologist at the Stellwagen Bank National Marine Sanctuary. Past research has assessed ocean noise sources individually. The animations Clark's team has created enable assessment of cumulative impacts from many sources, over time and across extended distances. This new perspective may well influence the location of future shipping routes, as well as offshore wind farms and new oil and gas developments.