A federal court judge in Honolulu heard arguments yesterday in a lawsuit seeking to stop a series of Navy anti-submarine warfare 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 nonclassified 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 board the Pearl Harbor destroyer USS O'Kane this morning to observe midfrequency sonar operations.

The court case follows two recent rulings on the West Coast that dealt the Navy setbacks in its use of active sonar, which sends sound waves into the water. Its effect on marine mammals is hotly debated by the Navy and environmental groups.

The Navy said it already takes measures to keep a lookout for whales and dolphins off Hawai'i, while environmentalists say more needs to be done, including not training within about 15 miles of the coastline where humpback whales congregate.

Yesterday's hearing stemmed from a lawsuit filed in May 2007. The Ocean Mammal Institute, Animal Welfare Institute, KAHEA, Center for Biological Diversity and Surfrider Foundation filed a legal challenge to the Navy's plan to use high-intensity sonar in a series of undersea warfare exercises in Hawai'i's waters.

Ezra asked for additional information from the Navy by Friday, and asked the plaintiffs to provide comments on it by Feb. 20. The plaintiffs want a preliminary injunction to prevent the training.

Among the questions Ezra wants the Navy to answer are why certain mitigation measures undertaken for Rim of the Pacific war games off Hawai'i in 2006 are considered inappropriate for the series of anti-submarine warfare exercises.

The Navy wants to continue providing the training off Hawai'i for strike groups of aircraft carriers and amphibious ships that leave from the West Coast, head into the western Pacific and then often operate in the Persian Gulf. Three of the exercises were conducted last year.

The Navy plans to conduct up to 12 such exercises over the next two years. The first of those is planned off Hawai'i in late March.

Typically, surface ships pulse the ocean with sonar as crews practice searching for foreign diesel electric submarines.

Paul Achitoff, an Earthjustice attorney representing the plaintiffs, said after the hearing that the mitigation measures being sought for the 200,000-square-mile Hawai'i Operating Area would not cause the Navy to deploy untrained forces.

"They want the option to go anywhere anytime (for training), and we're saying, sorry, you can do better than that," Achitoff said.

Another mitigation measure being pursued is for sonar training to be excluded during humpback whale calving season from November to May. Most of the measures have been used at various times in the past by the Navy, Achitoff said.

Capt. Bruce Stewart, director of operations for U.S. Pacific Fleet, said Hawai'i has unique deep- and shallow-water environments to conduct anti-submarine training. Worldwide, 300 of 380 submarines operated by more than 40 nations are quiet diesel electric models, he said.

The Navy is doing a "great job" working with available information, Stewart said, and is spending $14 million a year to get a greater understanding of sonar's effects on whales and dolphins.

The Navy said it uses two dedicated observers on each ship emitting sonar to look for whales with binoculars. Sonar also is powered down if whales are spotted, and turned off completely within 200 yards.

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

Last week, a federal judge in Los Angeles prohibited the Navy from using sub-hunting sonar in whale-populated areas off California, while a San Francisco judge issued a preliminary injunction limiting the use of low-frequency sonar.

Reach William Cole at wcole@honoluluadvertiser.com.