Turning Down the Noise

Several species of whales congregate around the Channel Islands off Santa Barbara, Calif., attracted by the region’s abundant feeding environment. The area was designated as a national marine sanctuary in 1980 to help protect its natural beauty and rich resources. But the sanctuary also happens to be located directly in the tracks of shipping traffic to the ports of Long Beach and Los Angeles, one of the busiest commercial maritime hubs in the world.

John Hildebrand and his colleagues in the Whale Acoustics Laboratory at Scripps Institution of Oceanography at UC San Diego have conducted research in the area and are uncovering new information about noise from ships and their impacts on marine mammals, which rely on sound for communicating, feeding, mating, and other key life functions.

Hildebrand and his colleagues will publish a study in the September issue of the Journal of the Acoustical Society of America (JASA) that investigates the magnitude and potential effects of chronic noise in marine habitats. Their study took advantage of a dramatic downturn from 2007 to 2010 in ship traffic in the Santa Barbara Channel, and the corresponding decline in noise, when a double-punch of economic recession and new fuel regulations took hold.

Hildebrand calls the noise downturn a large field experiment, not unlike the three-day airline grounding after the 9/11 attacks that gave scientists an unprecedented opportunity to study climate conditions in the absence of contrails, the vapor trails from jets.

“We had no control over this huge sea experiment but it’s as if we had a giant knob that controls the number of ships passing through the Santa Barbara Channel and someone said: ‘Let’s turn the knob down and see what happens,’” said Hildebrand.

Hildebrand and his group deployed a high-frequency acoustic recording package (HARP) near the Channel Islands to capture sounds in the undersea environment. That information was synthesized with data from an automatic identification system (AIS) that revealed the types of ships in the area and their speeds of travel.

A January 2012 JASA study by Hildebrand, his former student Megan McKenna, and their colleagues set the stage by defining how much noise each type of ship produces. The follow-on study then evaluated the overall noise environment around the Channel Islands. On average, the researchers found that shipping activity produces roughly one decibel of background noise per ship, per day. With the economic recession and new fuel regulations—which caused ships to avoid the Santa Barbara Channel—ship traffic spiraled downward so that about 12 fewer ships sailed through the channel each day and the average sound levels dropped by 12 decibels.

The results of both papers, said Hildebrand, reveal that the bulk of noise is generated from large container ships that travel at high speeds. Not only may such noise impair marine mammals’ ability to communicate with one another, it contributes to their stress levels and is thought to prompt whales to surface to avoid the noise, risking collisions with ships in the busy shipping lanes. In 2008, the Scripps Whale Acoustics Lab, in collaboration with John Calambokidis of the Cascadia Research Collective, initiated a research program to understand the impacts of noise from large vessels on blue whales. The research uses bio-logging technology to monitor blue whale behavior in the presence of ships. Although the research is still ongoing, preliminary results offer valuable insight on not only the behavioral reactions of this endangered species to ship noise, but also their vulnerability to ship strikes.

Just as it’s illegal for ships to come into coastal waters and discharge oil or other waste, Hildebrand believes noise pollution should be similarly curtailed, similar to jet noise restrictions surrounding airports. To address the economic impacts of reducing noise from ships, Hildebrand believes new ships could be built with advanced technology designed to reduce noise output.

“Sound is a really important sense for everything in the ocean, for fish and marine mammals and probably smaller organisms,” said Hildebrand. “They congregate in the Channel Islands region to feed, so if there is a place we want to protect from noise pollution, this would be it.”

-- Mario C. Aguilera