California Coast & Ocean

“Cumulative Nightmare”
Scientists concerned with the effect of shipping noise on marine animals are careful to point out that little specific evidence exists on how it affects them. It’s difficult to observe marine animals, much less conduct controlled experiments with them. Researchers discovered that sonar affects certain types of whales only because several high-profile strandings correlated closely in time and space with military exercises. Even in those cases, they haven’t determined precisely what caused the animals to strand or what killed those that died.

“We can’t necessarily identify whether or how many animals have been harmed [by shipping noise], or to what extent their reproductive behavior has been compromised,” Southhall said. “We also don’t know precisely how some animals can adapt to noise, though we believe they can, to some degree. They may simply tolerate shipping noise, trying to get by as acoustic animals in an ever more cluttered acoustic environment.”

Studies have, however, determined that loud noises within an animal’s frequency range can cause hearing loss; they can also cause marine animals to avoid breeding or feeding grounds, or to change course while migrating. In a 1998 study performed for the U.S. Navy by researchers Peter Tyack of Woods Hole Oceanographic Institute and Christopher Clark of Cornell University, gray whales migrating along the California coast avoided playbacks of low-frequency sonar. Another study published in 1984 in the book The Gray Whale (Academic Press, Orlando) found that whales stopped gathering to breed at Guerrero Negro Lagoon in Baja California during a period of increased dredging and commercial shipping activity from 1957 to 1967. After the activity declined, they gradually returned.

Exposure to loud noises has also been shown to alter animals’ patterns of communication. “There have been cases where whales made louder and longer sounds when noise levels were increased,” said Dave Mellinger, an associate professor at Oregon State University who specializes in analyzing whale sounds.

One of the potential effects that concerns scientists the most is masking, where the level of background noise increases to the point that it drowns out animals’ ability to communicate and hear key sounds within their frequency range. “Shipping noise tends to be a pretty low frequency, so animals that make their calls in that range are probably getting drowned out at a distance,” said Mellinger. The phenomenon has the potential to affect a large number of animals. “The area over which masking would occur is almost surely significantly greater than it is for disturbance of behavior,” said Southall.

Marine animals as varied as whales, fish, and invertebrates already suffer from myriad human-caused impacts, including overfishing, vessel strikes, red tides, pollution, marine debris, and the effects of global warming. Noise from shipping traffic--and other sources--is yet one more stressor. “At some point, it becomes a cumulative nightmare,” Steiner said.

“To me, it’s not really sufficient to say ‘We don’t know if it’s a problem’ and then not do anything about it,” said Douglas Nowacek, an assistant professor of oceanography at Florida State University who studies marine mammals’ use of sound. “Given how important sound is to marine mammals, there’s a very good chance that [shipping noise] could be a problem.”