In this March 28, 2018, file photo, a North Atlantic right whale surfaces in Cape Cod bay off the coast of Plymouth, Massachusetts. Credit: Michael Dwyer | AP

Federal regulators don’t believe a Maine plan to reduce risk to endangered whales goes far enough, and that means fishermen in the state could face more restrictions.

Maine officials submitted a plan to the federal government designed to meet a requirement to better protect rare North Atlantic right whales from entanglement in lobster fishing gear. The whales number only about 400 and can die if ensnared in the gear, which is used to trap one of Maine’s best known and most valuable natural resources.

The National Oceanic and Atmospheric Administration notified the state in a Jan. 10 letter that its proposed package of measures would result in no more than a 52 percent reduction in risk to the whales. The required goal is 60 percent, said the letter, which was written by Michael Pentony, regional administrator for NOAA’s National Marine Fisheries Service’s Greater Atlantic Regional Fisheries Office.

NOAA will have to consider additional measures to protect whales, Pentony said. Much of the rest of the letter was complimentary, and it also said that the U.S. government is working with Canada to reduce risk to the whales. Many lobstermen have cited the risk the whales’ face from Canadian fisheries as a major concern.

The U.S. will “stress that the right whale population cannot recover unless human-caused serious injuries and mortality of right whales are reduced to sustainable levels on both sides of the border,” Pentony wrote.

The assessment from NOAA means there’s still work to do on the right whale plan, said Jeff Nichols, a spokesman for the Maine Department of Marine Resources. The state spent months meeting with fishermen and crafting the plan, which some fishermen have said was already too punitive to their industry.

The proposal would not have changed fishing rules in inshore areas, but it would have reduced trap lines offshore, where the whales are more at risk to entanglement. It also included requirements for weak points in the trap lines that would make it easier for whales to get free.

The Maine Lobstermen’s Association did not return calls seeking comment. Maine is by far the biggest lobster fishing state in the U.S.

The industry is dealing with numerous stresses right now, including complicated trade relations with China, but is also coming out of a decade in which the volume and value of catch shattered previous records.

Right whales were decimated during the whaling era — which lasted until the early 20th century — when they were hunted for their oil. The population has declined in recent years, as the species has struggled with years of high mortality and injury from entanglements and ship strikes and low reproduction.