The United States Navy must reduce sonar levels in the oceans under a court decision by the Ninth U.S. Court of appeals. To comply, the Navy will need to scale back their use of low-frequency sonar in the Atlantic, Pacific and Indian oceans and the Mediterranean Sea.

The ruling on Friday, July 15 concluded that U.S. officials have wrongly allowed the Navy to use sonar at levels that could harm whales and other marine mammals in the world’s oceans.

Sonar, used to detect submarines, can injure whales, seals and walruses and disrupt their feeding and mating.

Military sonar, like that used by whales and dolphins, works by blasting sound through the water, thereafter gathering information on what’s ahead once the blast hits something and returns. Navy sonar is known to reach up to 235 decibels, far exceeding the human threshold before hearing damage of 85 decibels. Even at a distance of 300 miles sonar can reach 140 decibels, and anything above 140 vibrates internal organs and causes damage.

Environmental groups led by the Natural Resources Defense Council filed the lawsuit in San Francisco in 2012, arguing that the Obama administration had approved emissions at sound levels that violated the Marine Mammal Protection Act. A federal magistrate disagreed but was overruled Friday by the appeals court, which said government officials had disregarded their own experts’ warnings about the potential impacts of sonar.

Under the 2012 standard, which is scheduled to expire in 2017, the National Marine Fisheries Service required the Navy to reduce sonar levels in areas known to have high populations of marine mammals, but did not order protections in other areas where their presence was uncertain. Those included some offshore zones that had been protected in the past, and others listed by scientists as likely habitats, the court said.

The protected zones showed a “bias toward U.S. waters,” the court said, with several zones on the Atlantic and Pacific coasts of the United States but none on the Pacific coast of South America and only a scattered few in other waters.

“The result is that a meaningful proportion of the world‘s marine mammal habitat is under-protected,” Judge Ronald Gould said. He said the government had failed to comply with a law that requires it to make sure its peacetime oceanic programs have “the least practicable adverse impact on marine mammals.”