The Navy is holding a public meeting today as it re-evaluates the environmental impacts of training, research and testing — particularly from sonar and explosive sound effects on marine animals — over a wide swath of ocean between Southern California and the Hawaiian Islands.

The last such study provided the framework for Navy activities from 2013 to 2018. The next will support training beginning in 2018.

“The Navy acknowledges the importance of certain habitats for species and stocks of marine mammals, particularly for certain life stages, and has balanced the need for certain training and testing environments needed in order to achieve readiness,” the service said in a new draft environmental report.

Excluding the Southern California sites, the Hawaii Range Complex training area alone is huge — encompassing an area approximately 1,955 by 1,840 miles.

Environmental groups and the Navy in 2015 settled two cases challenging the training and testing, “securing long-sought protections for whales, dolphins and other marine mammals by limiting Navy activities in vital habitat,” the Center for Biological Diversity said at the time.

The Navy said in the new draft analysis that because marine animals would typically experience only a small number of behavioral responses per year due to acoustic stress, “population level effects are unlikely.”

For the current training period, the Navy said major training exercises called “composite training units” were assumed to require 1,000 hours of hull-mounted midfrequency sonar. But the Navy said it determined that was an overestimation, and now is calling for 600 hours of sonar training per composite training unit exercise.

Annual hull-mounted midfrequency sonar hours for composite training, anti-submarine warfare tracking and other sonar training and maintenance would drop to 6,701 hours from 11,888, the Navy said.

The Navy also said it would extend the season for the Humpback Whale Cautionary Area — where permission is required prior to the use of any surface ship hull-mounted sonar use during training and testing from Dec. 15 through April 15 — to Nov. 15 through April 15.

David Henkin, an attorney for Earthjustice in Honolulu, which brought one of the court cases against the Navy training, said Friday one positive development in the new study is that the “Navy has recognized that they need to be looking at time and area limitations on their activities in order to protect biologically important areas.”

In the settlement hammered out in 2015, the Navy agreed that it was operationally feasible and consistent with its mission to limit activities in certain sensitive areas around the Hawaiian Islands and off Southern California, Henkin said by phone.

“The bad news is that the limitations that they are proposing for this next round of training are less protective than what they agreed to in 2015,” Henkin said.

An important area is the Alenuihaha Channel between Maui and Hawaii island, he said. Under the settlement, training was allowed. But major training exercises were limited, according to Henkin.

What the Navy is proposing now is “no limitation at all on how much training and testing that they do in that area — which is really critical for a lot of our islands-specific marine mammals, including the critically endangered insular false killer whale,” Henkin said.

The Navy said in the draft report that the “settlement measures were derived pursuant to negotiations with plaintiffs” and were not evaluated on the best available science.

Henkin said that under the Endangered Species Act, Marine Mammal Protection Act and National Environmental Policy Act, “the Navy needs to figure out the maximum amount of protection that it can provide to marine mammals and endangered species — and at the same time protect the nation. It’s not an either/or.”

The more than 3,000-page draft environmental impact statement/overseas environmental impact statement is available at hstteis.com. Public comments can be sent by email.

The meeting will be from 4 to 8 p.m. at the Oahu Veterans Center, Fred Ballard Hall, 1298 Kukila St.