Maine’s plan to protect right whales does not go far enough to reduce the risk of entanglement in lobstering gear, according to federal regulators.

The National Marine Fisheries Service has concluded that Maine’s plan to use a combination of weak rope and a 25 percent reduction in the number of buoy lines in state waters achieves, at best, a 52 percent risk reduction, while federal regulators are demanding a 60 percent reduction.

“Because your proposal does not meet the 60 percent risk reduction target, we will be obligated to consider additional measures through our federal rulemaking,” said Michael Pentony, regional administrator of NMFS’s Greater Atlantic Regional Fisheries Office.

The tone of Pentony’s Jan. 10 letter to Maine Marine Resources Commissioner Pat Keliher is complimentary, singling out the plan’s emphasis on protection measures in offshore waters, where the risk to whales is greatest, yet still including weak links near the shore as a precautionary measure.

But Keliher made it clear Tuesday during a legislative briefing that the letter was bad news for Maine.

“They are not accepting this proposal,” Keliher told the Marine Resources Committee. “We expect them to do more on top of it. What that means, we don’t know. So there is a lot of work to do still … but they are holding the line at 60 percent.”

The state’s biggest lobster trade group, the Maine Lobstermen’s Association, did not respond to an email seeking a response to Pentony’s letter late Tuesday. The group didn’t support Maine’s latest plan, which it said was better than earlier versions, but still blamed Maine lobstermen for something they didn’t do.

Maine’s whale plan calls for cutting the number of buoy lines that could entangle whales by setting a minimum number of traps fished on each line, with the minimum number of traps increasing farther from shore, and requiring weak points in buoy lines to help entangled whales break free.

Weak points are sleeves, splices and knots added to surface-to-seabed ropes that reduce the strength of the line so adult whales can break free if entangled. Maine counted on weak points to make up for its decision to propose a 25 percent buoy line reduction compared to NMFS’ endorsed 50 percent cut.

The plan also seeks federal approval for alternative fishing restrictions, or conservation equivalencies, that achieve the same level of risk reduction in cases where a statewide whale-inspired fishing rule would put lobstermen in physical danger or run needlessly afoul of regional fishing practices.

The state argues that careful use of alternative protections to achieve the same conservation benefit could protect whales, fishermen and the state’s $485 million-a-year industry. NMFS shot down the concept when Maine proposed it five years ago, but in his letter, Pentony now said regulators want to learn more.

The letter does not say exactly how NMFS would close the risk reduction gap. It said only that the interim federal rule it will issue in July will complement protection measures proposed by the individual lobstering states. It also will include measures to reduce offshore entanglement risks in federal waters.

In his legislative briefing, Keliher warned that federal regulators have two blunt management tools at their disposal should Maine decide to stop negotiating, throw up its hands and fight: fishery-wide trap reductions and area closures like the one implemented in Massachusetts Bay.

Under threat of multiple lawsuits, NMFS is under pressure to take significant steps to protect right whale.

Scientists believe only 406 right whales remain. The species has been on the brink of extinction before, most recently in 1992, when its numbers fell to 295. It rebounded to about 500 in 2010, but low calving rates, ship strikes and entanglements have since sent its numbers tumbling.

Regulators now believe that even one death a year could doom the right whale to extinction.

Since 2017, at least 30 right whales have been seriously injured or killed, mostly in Canada. Eight incidents were attributed to ship strikes, including one in U.S. waters, but none can be linked to the Maine lobster industry. The most recent known Maine entanglement occurred in 2004, but the whale survived.