After years of advocacy, some 17,500 square miles of ocean around the main Hawaiian isles will be designated as protected critical habitat for Hawaii’s endangered false killer whales.

The new rule by the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service was published Tuesday in the Federal Register and goes into effect Aug. 23.

The Center for Biological Diversity, an Arizona-based nonprofit that has been pushing for protection of the whales — which are actually members of the dolphin family — celebrated it as a milestone.

“It’s a very good day for the false killer whales,” said Brett Hartl, the center’s government affairs director. “Getting critical habitat is a very important step, and a very useful tool to help get a species on the path to recovery. This is progress, and now we need to keep moving forward and make sure we do what needs to be done to protect the false killer whale and its habitat from harm.”

Only about 150 false killer whales, or Pseudorca crassidens, remain in waters around the main Hawaiian isles today.

The protected habitat for false killer whales includes ocean waters from Niihau to Hawaii island, at depths of about 150 to 10,500 feet.

This habitat must offer the false killer whales adequate space for movement within the ocean shelf and slope around the main Hawaiian isles, as well as provide enough prey species and water free of harmful pollutants and chronic noise.

Fourteen areas were excluded — 13 requested by the Navy and one by the Bureau of Ocean Energy Management. The Navy requested that part of the Alenuihaha Channel, an area north of Molokai, and the Kahoolawe Training Minefield, along with other areas, be excluded.

The bureau’s requested area included two sites — one off of Oahu’s South Shore and another off Kaena Point — for offshore energy projects.

“What they’ve done is probably not exactly what we hoped for,” said Hartl when asked about the exclusions, “but I think at the end of the day, the critical habitat that the false killer whale receives is a huge step in the right direction.”

Some of those matters can also be revisited, he added.

In 2010 the center announced the establishment of a take reduction team to look at ways to reduce harm to the false killer whales caused by commercial longline operations. The move came after litigation against the National Marine Fisheries Service for its failure to protect the mammals.

False killer whales often take bait and catch from fishing lines, resulting in unintentional hookings, entanglement and injuries.

False killer whales, which are black or dark gray and distinguished by conical heads that give them their name, were listed as an endangered species in December 2012. They are gregarious mammals that form strong, social bonds and share captured prey, according to NOAA. The oldest estimated age is 58 for a male and 63 for a female.

The designation of protected habitat for the false killer whales comes at a time when the Endangered Species Act is under threat of revisions that could weaken its future effectiveness.

Some of those revisions, said Hartl, would include the weakening of protections for critical habitats, affecting false killer whales.

“That’s a fight for another day,” he said. “We’ve done right for the killer whale today.”