Three years of study at Stellwagen Bank National Marine Sanctuary has shown underwater noise, mainly from ships, has significantly reduced the ability of right whales to communicate with each other. But more study is needed to say how the endangered marine mammal's survival is affected.
Each year, North Atlantic right whales, with their distinctive head markings, migrate along the western Atlantic coast from calving grounds off Florida to feeding areas in Nova Scotia.
The federal government has named Massachusetts Bay and Cape Cod Bay as critical habitats for the whales, part of the protections required by federal law. Up to 550 whales exist today worldwide, a federal report stated this week.
A paper published Wednesday in the journal Conservation Biology compared the current levels of underwater sound with those of almost 50 years ago, when waters were quieter. The results showed that, on average, 63 to 67 percent of right whales' "communication space" in the sanctuary and surrounding waters has been lost.
Communication space is the area over which an animal can be heard.
The loudest sound to drown out whale calls are bubbles from ship propellers, said Leila Hatch, a marine ecologist with the sanctuary and the paper's lead author.
The research was led by the NOAA and the sanctuary, in cooperation with the Cornell Lab of Ornithology and Marine Acoustics Inc. in Rhode Island.
Eighty-nine whales were documented in the study.
"We still need to know what that loss of communication means," Hatch said Wednesday, both for individual whales and the whole population. "Those are big additional leaps we need to make. We're looking for the links."
Right whales make several calls, but researchers documented the "up-call" in the study because it's the most prevalent used in and around the sanctuary, especially in the spring when the animals are feeding, Hatch said.
The up-call is a distinct, rising "whoop" that lasts about a second, according to the Right Whale Listening Network, part of the Cornell lab. Researchers believe the up-call is a whale's way of making small talk and letting others know what's going on with activities such as finding food, mating, navigating, avoiding predators and taking care of their young.
The loss of up-call information might mean, for example, a drop in the number of calories a right whale consumes, and that could possibly affect a whale's ability to have a calf, Hatch said.
The study, from 2007 to 2010, occurred during a time and place where the right whales are plentiful -- at Stellwagen Bank during peak feeding times. Stellwagen Bank is an 842-square-mile region of deep water at the mouth of Massachusetts Bay, known for its fertile fishing grounds and whale populations. The area is about three miles north of Cape Cod.
Researchers used sound recorders placed on the ocean floor to monitor ambient noise levels, measure levels of sound associated with vessels and detect and locate calling whales. They tracked wind speed from existing buoys in the region and used an existing on-board computer program on commercial ships to link underwater sounds to specific vessels.
In 2010, in the journal Biology Letters, Syracuse University assistant professor Susan E. Parks and others wrote a paper saying individual North Atlantic right whales adapted during periods of increased underwater noise by raising the volume of the calls.
Parks, who responded by email Wednesday, said she was conducting research where there was poor phone and Internet service and hadn't had a chance to catch up with the Stellwagen Bank paper.
The possibility of adaptation to louder noise was addressed, though, Hatch said.
"All behavioral changes usually have some cost," she said. "It may be that animals have some flexibility in what they can do. We have to remember, though, that they are constrained, by cost in energy (used) and by physiology, like how loud they can go."
North Atlantic right whales are complex animals that humans do not full understand, Charles "Stormy" Mayo, director of right whale habitat studies at the Provincetown Center for Coastal Studies, said Wednesday.
"We certainly don't understand how exactly this sort of problem will affect the animals, or what it will disrupt. It seems highly likely that not being able to hear from the distances they once did, for which they became adapted, would seem to have a detrimental effect."
The Provincetown center handles the bulk of North Atlantic right whale studies, other than acoustics research, in Massachusetts waters.
The results in Wednesday's paper also serve as an example of a larger problem, Mayo said. "It's one of an infinite number of places in the world's oceans where ships travel and marine mammals need their acoustic space."
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