First published in the MLA Newsletter, October, 2012.
We all rely on senses (sight, smell, taste, touch, and sound) to navigate our world. When one of those senses does not work well (i.e. limited sight in a dark room), other senses compensate. For right whales, sight is limited by the amount of light able to travel through the water. This allows whales to only see shadows and movements, not defined shapes or colors. Instead of depending on their limited sight to navigate their watery world, right whales and many other marine species rely on sound. Right whales communicate with various sounds to find mates, food, and to maintain the herd while migrating. If their ability to communicate is reduced, the right whales’ way of life could be in even more danger than it already is.
Unfortunately, the noise in the Gulf of Maine has been increasing for a number of years. “Noise levels in the ocean are increasing. It’s almost doubled every decade in the last forty years,” said Christopher W. Clark, MSEE PhD, I. P. Johnson Director, Bioacoustics Research Program at the Cornell Lab of Ornithology and Senior Scientist in the Department of Neurobiology & Behavior at Cornell University and co-author of a published paper on restricted communications for right whales. Sound travels more efficiently in water than it does in air, making noise, even miles away from the source, a loud threat to marine animals’ communication. Clark compares the noise to being in the city versus in the country. “When you are at camp out in the woods, it’s really quiet. You could hear a pin drop. You can easily have a conversation with someone. Then imagine trying to have that conversation while standing on the side of the street in a city. You have a lot more background noise making it harder to hear what the other person is saying.”
Clark said that right whales are now “all living in the city” because of the increased noise in the ocean. Where is all this noise coming from? “Almost all of the noise is coming from commercial shipping,” Clark said. “The sound from a ship can travel hundreds of miles underwater. As the ship moves farther away, sound decreases, but it decreases logarithmically with distance. That means at first, there will be a big decrease in noise. Then the rate at which noise decreases slows down.” He said that, for example, a nearby ship may produce 180 decibels. When that ship is one kilometer(0.6 miles) away the sound level drops to 120 decibels. But then at ten kilometers(6.2 miles)the level only drops to 110 decibels and at 100 kilometers (60.2 miles)it drops to 100 decibels. All of this translates into a lot of noise “smog” in the ocean allowing right whales very little space in which to communicate clearly. “We found that for at least 60 percent of the time whales are not able to communicate because there is so much noise,” Clark said.
Clark said that the May 2012 report he co-authored with Leila Hatch (NOAA) as the primary author, “Quantifying loss of acoustic communication space for right whales in and around a U.S. national marine sanctuary,” aims to alert people that increasing ocean noise is a critical problem. The researchers, in collaboration with National Oceanic and Atmospheric Administration (NOAA), recorded noise in the Stellwagen Bank National Marine Sanctuary during the spring of 2008 using marine autonomous recording units (MARUs), also called pop-up buoys.
The buoys record sound with an external hydrophone that is connected to an internal hard drive. The buoy is anchored to the ocean floor and can stay there for three to six months, passively recording sounds the entire time. When it is time to retrieve the buoy, a signal is sent to it, telling the buoy to sever its anchor connection. The buoy then pops to the surface. Once the hard drive is removed from the buoy, the recordings are downloaded and digitized. Clark’s role in this study was to develop algorithms to explain the amount of noise recorded and how that noise affects right whales. “We want to know at any given time, what is the communication network and how is it working?” Clark explained. “We found that the background noise [that was recorded] was higher than expected. Should we be worried about this? I think so because it affects more than just right whales.”
One of the concerns Clark shared was the potential for the east coast to be opened to oil and gas exploration. “Exploring means setting off explosions every ten seconds or so, explosions that can be heard hundreds of miles away. We don’t know the chronic, long-term effects of noise on marine life, including fish,” he said. “Noise is just another insult we’ve imposed on the ocean without knowing the consequences.”
Clark said the next step is to produce a scientifically accurate chart of ocean noise. “NOAA is doing some of the work on this right now. We hope to have a chart, similar to a nautical chart, of the sound levels in the ocean in two years.” He said the paper published this past spring was an effort to let people know how much underwater noise has increased in recent decades and how it could negatively affect marine life. “It’s time to recognize [the problem] and figure out what the scale of the problem might actually be,” Clark said.
For more information, go to www.listenforwhales.org.Category: Science