PORT ANGELES — The Navy is preparing a supplement to an environmental impact statement that would increase use of sonar in the Northwest Training and Testing Study Area.

In January, the Navy released a draft environmental impact study of training exercises and use of sonar and explosives in the training zone that includes areas off the North Olympic Peninsula’s Pacific Coast — including the Olympic Coast National Marine Sanctuary — off Indian Island and in the Strait of Juan de Fuca.

By December, the Navy expects to release a supplement to that draft study, recommending increasing the use of sonobuoys, and open it to public comment.

Critics have worried that sonar could harm whales and other sea mammals.

The draft environmental impact study and supplement for the Northwest Training and Testing Study Area are separate from a controversial electronic warfare training project in the Olympic Military Operations Area that the Navy is seeking U.S. Forest Service permits to enact.

The 1,818-page draft environmental impact study, which is to support the Navy’s request for the renewal of its five-year Marine Mammal Protection Act permit, is at http://tinyurl.com/PDN-Sonobuoy2.

Comments on the original draft study were accepted between Jan. 24-April 15 and will be considered in the development of the final statement, the Navy said.

In late October, the Navy announced that updated training requirements would result in changes to the project.

The supplement will present those changes “and significant new information relevant to environmental concerns,” according to a statement from Navy Command Northwest.

The Navy will review the increased use of the sonobuoys as part of its supplemental review, Navy spokeswoman Liane Nakahara said Friday, adding that it is expected to be ready for public review in December.

Sonobuoys are both active, meaning they emit sonar, or inactive, meaning that they only collect sounds. They collect and transmit information about the marine environment and potential threats and targets.

Officials with the Olympic Coast National Marine Sanctuary, which consists of 2,408 square nautical miles off the Olympic Peninsula coastline, were unavailable Friday for comment on the proposal.

In the draft environmental review that will be supplemented, the Navy says it is exempt from marine sanctuary prohibitions but “will avoid, to the maximum extent practicable and consistent with training and testing requirements, adverse impacts” to the sanctuary area.

Bombing exercises take place outside the sanctuary, it adds.

The preferred alternative presented in the draft study released in January called for new biennial training exercises conducted in the offshore area, biennial mine warfare exercises in Puget Sound in support of homeland defense, and training with and testing of undersea systems, subsystems, and components in Puget Sound, among other changes.

In the draft document released in January, the preferred alternative would increase the tempo of new buoy testing activities from 54 activities with 510 buoys, to 59 activities with 561 buoys.

In a 2008 environmental impact statement, which is at http://tinyurl.com/PDN-Sonobuoy1, sonobuoys are described as 6 inches in diameter and 3 feet long.

In those with explosives, “the charges explode, creating a loud acoustic signal,” according to the 2008 study.

“The explosion creates an air bubble of gaseous by-products that travels to the surface and escapes into the atmosphere.”

The study determined that the sonobuoys may affect, but likely not adversely, blue whales, fin whales, humpback whales, North Pacific right whales, Sei whales, sperm whales and sea otters.

The impact on the Southern Resident killer whale was listed as ranging from may affect, but not likely to adversely, to no effect at all.

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Senior Staff Writer Paul Gottlieb can be reached at 360-452-2345, ext. 5060, or at pgottlieb@peninsuladailynews.com.