PORTLAND – The crew of a whale-watching vessel violated the law and endangered the life of a mother whale by partially freeing her from fishing gear, a federal fisheries spokeswoman said Tuesday.

Crew members aboard the Nautilus snipped 300 feet of rope from the 65-foot humpback’s dorsal fin after they spotted the whale and her calf swimming alongside their vessel 12 miles offshore on Sunday.

The 49 passengers cheered the whale’s disentanglement, and a TV camera crew later gathered at the Kennebunkport dock to document it. But there were a number of problems with the rescue, and crew members violated federal law by taking the matter into their own hands, said Teri Frady, spokeswoman for the National Marine Fisheries Service.

The whale’s life is still in danger because several wraps of rope remain tangled around her pectoral fins, Frady said. And the crew’s removal of 300 feet of rope makes it harder and more dangerous for rescuers to get to those fins.

Furthermore, the removed rope, which could have helped rescuers investigate the entanglement, is now missing, making it harder for officials to determine what happened, Frady said.

“We need to recover the gear,” she said from her office in Woods Hole, Mass. “It’s not there anymore.”

Scott Landry of the Center for Coastal Studies in Provincetown, Mass., said the Nautilus crew should have called the Coast Guard and then stayed near the whale while taking video and photographs to document its condition. Investigators did get photographs from the scene.

“It’s now very hard for us to get a hold of the animal,” Landry said. “What makes this a bit more scary is that if Sickle is in danger, then her calf is in danger as well.”

The center is the only group on the East Coast authorized by the federal government to disentangle humpback whales, a federally protected endangered species.

James Harkins, skipper of the Nautilus, defended his crew’s decision to disentangle the whale, named Sickle.

“I know there’s a little negativity,” he said. “It was an extraordinary event for us to have this whale come to us for help.”

Harkins said he is “99 percent sure” that the whale will free herself from the remaining 30 to 40 feet of rope wrapped around her fin.

Harkins said the removed rope, which had no identification, was placed on the dock in Kennebunkport. He refused to speculate on what happened to it.

Officials said disentangling a whale is a violation of both the federal Marine Mammal Protection Act and the Endangered Species Act, but no action is likely to be taken in this case.

“There’s a lot of things you can do to help,” Frady said. “Actually disentangling a whale is not one of them.”

Anyone with information about the whereabouts of the rope removed from the humpback whale is asked to call (800) 853-1964.