Excessive ocean noise can hurt whales. Here's how.

Whales are among the loudest animals on Earth, but even they can be susceptible to harm from excessive or overly loud noise in the ocean.

Scientists have measured blue whales calls as loud as 190 decibels, volume that helps carry their songs and calls across great expanses of ocean.

To the human ear, anything over 120 decibels — about the volume of a siren while standing near the source — can cause immediate hearing damage and pain, according to The Centers for Disease Control and Prevention.

Despite the whales' volume, human-made sound in the ocean has been documented to affect their behavior and can, in some circumstances, cause them degrees of harm, according to experts.

In 2013, researchers funded by the U.S. Navy discovered that mid-frequency sonar sounds caused blue whales off the coast of California to change their diving behavior and temporarily avoid feeding areas.

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In 2000, sonar used by Navy ships during a training session in the Bahamas likely lead to the deaths of six whales, while other whales that stranded were pushed back out to sea, according to news reports at the time. Later necropsy reports released on the strandings revealed that the dead whales had hemorrhaging near the ears, according to the journal Science. An investigation revealed that a Navy sonar exercise was the most likely cause of their deaths.

Human-generated noise has long been a problem for ocean animals, many of whom hunt, mate and communicate by sound. Global shipping, oil and gas exploration, ocean construction and Navy operations all contribute to the new noisiness of the ocean, according to the National Oceanic and Atmospheric Administration.

In the worst cases, this noise can cause hearing loss for marine animals, cause stress and drive animals from migration routes or important feeding and breeding areas, according to NOAA.

Yet, there are no simple answers as to what level of manmade noise hurts whales, said Alba Solsona Berga, an acoustic ecologist at Scripps Institution of Oceanography at the University of California, San Diego. Solsona Berga studies the effects of sound on whales, particularly Navy sonar on beaked whales.

"Everything is super complicated, from one species to the next," she said.

The pitch and volume of sound, the distance from the animal, and the species of marine animal, all affect whether the noise could harm the creature, she said.

"We're seeing that there are differences in how they respond (to noise) between Southern California and the Atlantic," Solsona Berga said. "There are even differences and how they respond to noise within the same species."

Mass strandings are among the most rare responses by whales to noise, she said. But even noise that does not trigger strandings can cause other harm, she noted.

Noise "can affect their fitness and their survival," Solsona Berga said.

Like a person shouting over a crowd to be heard, whales "have to produce calls that are more intense to hear themselves (in a noisy ocean)," she said. "They have to do this call for a longer time or repeat them more often. And some even adjust the frequency range of their calls and they can be outside the normal range."

The federal Marine Mammal Protection Act makes disturbing marine mammals like whales illegal, but allows limited, permitted exemptions called "takes" under specific circumstances. Those exemptions include military operations, commercial fishing, oil and gas exploration, power plant operations, construction projects and seismic testing.

NOAA Fisheries has granted New Jersey offshore wind companies exemptions to the Marine Mammal Protection Act through what is called "incidental take authorizations," in order to complete their turbine projects.

So far, none of the companies have started turbine construction.

Amanda Oglesby is an Ocean County native who covers Brick, Barnegat and Lacey townships as well as the environment. She has worked for the Press for more than a decade. Reach her at @OglesbyAPP, aoglesby@gannettnj.com or 732-557-5701.

This article originally appeared on Asbury Park Press: Whales susceptible to excessive ocean noise that can cause harm