A federal court judge in Honolulu heard arguments this morning in a lawsuit that seeks to stop a series of Navy sonar exercises off Hawai'i unless additional precautions are taken to protect whales and dolphins.

U.S. District Judge David Ezra said he had received "top secret" information from the Navy, as well as non-classified materials, as he noted the complexity of the case.

Forty-five minutes were allotted for the hearing, but Ezra said the issues "couldn't be digested in 45 hours, quite frankly." Ezra and attorneys for both sides in the lawsuit will go out on a Navy ship tomorrow to observe sonar operations.

In May 2007, the Ocean Mammal Institute, Animal Welfare Institute, KAHEA, Center for Biological Diversity and Surfrider Foundation filed a legal challenge to the U.S. Navy's plan to use high-intensity sonar in antisubmarine exercises in Hawai'i's waters.

The Navy wants to continue providing anti-submarine warfare training off Hawai'i for strike groups of aircraft carriers and amphibious assault ships that leave from the West Coast, head into the western Pacific, and then often operate in the Persian Gulf region. The Navy wants to conduct up to 12 such exercises over the next two years.

Ezra asked for additional information from the Navy by Friday, and asked the plaintiffs to provide comments by Feb. 20. The Navy wants to conduct the first of the undersea warfare exercises off Hawai'i in late March.

Paul Achitoff, an Earthjustice attorney representing the plaintiffs, said outside the courtroom after the hearing that the mitigation measures being sought would not cause the Navy to deploy untrained forces.

Among the mitigation measures being sought are a reduction of sonar power in low-visibility, where whales might not be spotted, Achitoff said. The Navy also should stay away from coastal areas and shallows as it conducts sonar practice, he said.

Capt. Bruce Stewart, director of operations for U.S. Pacific Fleet, said Hawai'i's waters provide unique deep- and shallow-water environments to conduct anti-submarine warfare training in a world environment in which 300 of 380 foreign submarines are quiet diesel electric models.

Right now, the Navy is doing a "great job" working with available science on sonar impacts on marine mammals, Stewart said.

"We are good stewards of the environment," he said.

Reach William Cole at wcole@honoluluadvertiser.com.