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.