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.