A federal court judge in Honolulu today granted in part and denied in part environmentalists' calls for a preliminary injunction involving up to 12 Navy sonar exercises off Hawai'i over the next two years.

A lawsuit was filed seeking to stop the sonar exercises unless additional precautions were taken to protect whales and dolphins.

U.S. District Judge David Ezra noted that "this is an extremely complex issue on which there is still much uncertainty."

While the Navy disputes the factors associated with marine mammal strandings, "there is little disagreement that (mid-frequency active) sonar can cause injury, death, and behavioral alteration to these animals," Ezra said.

Among the requirements that Ezra ordered are "safety zones," including the need for the Navy to power down active sonar by six decibels when a marine mammal is spotted within 1,500 meters of a sonar-emitting vessel.

The sonar power must be stepped down the closer the animal is, and within 500 meters, all sonar transmission must cease.

Ezra's order also requires that each day mid-frequency active sonar is used, the Navy must monitor for the presence of marine animals for 60 minutes before sonar is employed.

The Navy must use three dedicated lookouts, and aircraft already being used for an exercise, or where practicable, to assist in monitoring.

Ezra also ordered that the Navy power down sonar when multiple factors are present, including rapid changes in bathymetry, when there are three or more sonar-emitting vessels, and if the sonar occurs in chokepoint channels.

Before initiating any exercise with sonar, the Navy will have to gradually "ramp up" sonar transmissions — something that the Navy said would harm its training, Ezra's order states.

Ezra said the weight of evidence points to avoidance of marine mammal habitat as the most effective means of minimizing sonar-related injury, and as such, avoidance of near shore areas is one generally accepted method.

He also said, though, that he is cognizant of the Navy's need to train in the littorals, or those near-shore areas of the globe, where quiet foreign diesel electric submarines pose a threat.

The Navy previously "recognized the value" of adhering to such exclusion zones, including a 25 nautical mile zone for Rim of the Pacific war games in 2006, Ezra said.

Ezra said a 12 nautical mile limit "may be reasonable," but decided to revisit the issue after the next coming exercise in March, which the Navy said would occur no closer than 40 nautical miles from shore.

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 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 previously 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.

The court order said at least 26 species of marine mammals frequent Hawaii's waters. The use of mid-frequency Navy sonar was determined to be a "plausible, if not likely" contributing factor to the mass stranding of up to 200 melon-headed whales in Hanalei Bay during Rimpac exercises in 2004.

High level acoustic exposures have been demonstrated to adversely affect marine mammals, resulting in injuries including ruptured hearing organs and behavioral modifications, according to Ezra's order.

The Navy has maintained it is a good steward of the environment and already takes steps to avoid impacts on whales and dolphins while also conducting crucial sonar training.

Reach William Cole at wcole@honoluluadvertiser.com.