BOSTON (AP) -- Researchers say increasing amounts of underwater noise, largely from shipping traffic, is enveloping rare right whales in "acoustic smog" that makes it harder for them to communicate.

The endangered North Atlantic right whale relies far more on sound than sight, using distinctive noises to maintain contact.

A paper by federal scientists and Cornell University researchers published Wednesday estimates that in the last 50 years, the area where the whales can effectively communicate in Stellwagen Bank and surrounding waters off Massachusetts has fallen by two-thirds because of the noise.

They say that's cutting down on the whales' ability to gather and share vital information that helps them find food, avoid predators, reproduce and protect their young.

Researchers say the next step is figuring out how to address the problem.