HONOLULU — An environmental group on Tuesday filed a lawsuit against the National Marine Fisheries Service to force a decision on whether it will put a population of rare dolphins living near Hawaii on the endangered species list.

Its species — called "false killer whale" even though it's a dolphin and doesn't look like a whale — is found in tropical and temperate waters worldwide. But scientists estimate only about 150 or 170 live in waters less than 90 miles off Hawaii.

"The administration's own scientists found that the whales run a high risk of extinction within 75 years. Every day that this listing is delayed is another day without steps being taken to protect them," said Michael Jasny, a senior policy analyst for the Natural Resources Defense Council, which filed the lawsuit at federal district court in Washington, D.C.

The National Marine Fisheries Service recommended 18 months ago that the population be listed. Under federal law, the agency had one year to decide whether to do so.

The agency has missed similar deadlines before, but Jasny said it's a "no-brainer" to list the dolphins.

"It represents our best chance to save them. Saving them could go a long way towards preserving the remarkable marine oasis of which they are a part," he said.

Fisheries service spokeswoman Wende Goo said the agency is waiting to receive a copy of the lawsuit. The agency will review the complaint and decide what to do next when it receives it, she said.

The animals are at high risk of inbreeding, a 2010 fisheries service study said.

They're also in danger of being inadvertently snagged by fishing lines. Studies showed Hawaii's longline fishing fleet was accidentally killing or seriously injuring an average of 7.4 false killer whales each year. This exceeds the 2.5 per year that the fishery could kill or seriously harm without affecting the population's ability to survive.

The fisheries service last year proposed new rules for the industry, including a requirement that it use a different style of hook to reduce the chance the fleet will hook the dolphins

Many longline boats have already started using the recommended circle hooks even before the federal government has formally adopted them.

Longline fishing vessels string a line in the ocean, ranging from one mile to 50 miles long, to catch fish. They run smaller lines with baited hooks off the central line and wait for bait to attract fish.

False killer whales have been getting caught because they like to eat the same fish the fishery is trying to catch — ahi, mahimahi and ono. They've been getting snagged when trying to eat fish hooked on the lines.