The US Navy is now using a particular type of sonar in more than half of the world’s oceans under an illegal permit. That sonar harms marine mammals like whales, dolphins, seals, and walruses. On Friday, the Ninth US Circuit Court of Appeals in California found that a 2012 regulation that allowed the Navy to use a low-frequency active sonar for training and testing violates the Marine Mammal Protection Act.

The court found that the National Marine Fisheries Service (NMFS), which gave the authorization, isn’t doing enough to avoid harming or killing marine mammals under the law. The Marine Mammal Protection Act calls for the "least practicable adverse impact" on marine mammals and their habitats. The court also found that the federal agency failed to protect areas of the world that its own government experts had flagged as "biologically important" to protect marine life. Such areas include the Galapagos Islands off the coast of Ecuador, the Papahanaumokuakea Marine National Monument off of Hawaii, and Challenger Bank off of Bermuda.

The Navy had been authorized to use the high-intensity long-range sonar — called low-frequency active sonar, or LFA — for five years across more than 70 percent of the world’s oceans, in areas of the Pacific, Atlantic, and Indian Oceans and the Mediterranean Sea. The NMFS has to set certain limits to activities, like military training, that could harm marine mammals. The goal is to reduce the impact on marine life to its lowest possible level.

The Navy uses LFA to detect quiet foreign submarines. The sonar involves the use of 18 speakers lowered hundreds of feet below the surface. It produces low-frequency sound pulses of about 215 decibels (dB), in sequences that last about 60 seconds. That can interfere over hundreds of miles with some marine mammals like whales, dolphins, and walruses that rely on underwater sound for navigating, catching prey, and communicating. LFA sonar can harm the animals by interrupting mating, stopping communication, causing them to separate from calves, and inflicting stress. Sounds above 180 dB can disrupt the animals’ hearing and cause physical injury. In 2005, 34 whales became stranded and died off in North Carolina because of nearby offshore Navy sonar training, according to Scientific American.

To limit harm, the NMFS requires the Navy to shut down or delay sonar transmission if there are nearby marine mammals. It also forbids the Navy to produce pulses of 180dB or more within about 14 miles of any coastline, or within 0.6 miles of several "offshore biologically important areas." All these regulations exist to try to minimize the impact that the use of LFA sonar has on marine mammals, to try to comply with the law. But the court found that the measures aren’t enough.

"This systematic underprotection of marine mammals cannot be consistent with the requirement that mitigation measures result in the ‘least practicable adverse impact’ on marine mammals," the court said.

One of the NMFS’s arguments is that too little data on marine mammal distribution is available to ensure protection of certain habitats. But even when the federal agency consulted with leading marine mammal experts, their opinion was disregarded, according to Michael Jasny, the director of the Marine Mammal Protection Project at the Natural Resources Defense Council (NRDC), one of the organizations that brought the case against the NMFS.

"The court soundly rejected that approach," says Jasny. "In doing so, it has ruled in ways that could significantly alter the way that the agency does business under the law." When enough data is lacking, the NMFS should err on the side of overprotection rather than underprotection, Jasny says.

This is the third time that the Navy’s authorization to use its LFA sonar has been challenged in court. In 2002, when the Navy first sought authorization for its LFA sonar system, and in 2007, plaintiffs and the Navy reached a court-ordered settlement allowing use of LFA in significantly reduced areas of the world's oceans, according to the NRDC.

"What the fisheries service did here was ... consistent with what until now has been an inadequate approach to mitigation that the scientific and conservation communities have frequently criticized the agency for," Jasny says.