San Diego

A court has ordered the US Navy to come up with an environmental plan before it extends the deployment of a submarine-detection system that some biologists say could disturb and harm marine mammals and fish.

The ruling by a federal judge in San Francisco could end a prolonged wrangle between the navy and environmentalists over the use of the sonar system (see Nature 413, 242; 200110.1038/35095188).

Environmental groups and the navy will meet on 7 October to work out terms for deploying the new sonar, which emits a low-frequency, 140-decibel sound wave that is able to pick up echoes from submarines hundreds of kilometres away.

On 26 August, Judge Elizabeth Laporte of the US District Court in San Francisco ruled that the navy did not have proper environmental permits to test and use the sonar system widely. Environmentalists greeted the ruling as a major victory in their long-running efforts to block its deployment. The navy, even as it complies with the ruling, will push Congress to change the law.

In her 73-page ruling, Laporte said that the case required a difficult balancing act between national security requirements and laws enacted to protect sea life. She declined to ban the sonar outright, but sought a permanent, court-approved plan to allow broader use of the equipment while protecting sea life.

The decision “recognizes that during peacetime even the military must comply with our environmental laws”, says Joel Reynolds, a senior attorney for the Washington-based National Resources Defense Council, the environmental group that led the lawsuit. The navy said that it was “concerned about the implications of the decision for national defence”.

Currently, the navy can only test and train with the new sonar system in a region covering two million square kilometres near Guam in the western Pacific Ocean. But the navy wants to use it in ocean habitats that are populated by whales and other species that are already suffering environmental pressures.

Other sonars that operate at higher frequencies have been linked to incidents in which whales, dolphins or porpoises were harmed or killed (see Nature 415, 106; 200210.1038/415106a).