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Scientists rescued a humpback whale entangled in ropes and bitten by a great white shark as the shark prowled the waters beneath them Saturday.

While conducting research on gases exhaled by humpback whales, Center for Coastal Studies researchers discovered a young whale on Stellwagen Bank, a popular feeding ground for whales about 5 miles north of Provincetown. The whale, hogtied from mouth to tail, was immobile at the surface of the water and had sustained a large bite wound on its left flank from the shark.

“I have only seen a shark attack a live whale once before, and that was a separated calf in Hawaii,” said Dr. Jooke Robbins, CCS director of Humpback Whale Research. “I have never seen it before here. They are most likely to target incapacitated whales [as in this case], sick individuals and otherwise vulnerable animals.”

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Rope was found running through the whale’s baleen and wrapped around its flukes, leaving it especially vulnerable, since it couldn’t fully use its tail for swimming or defense, Cathrine Macort, executive assistant at CCS, said in a release. CCS researchers do not know how long the whale had been entangled, she said.

When Dr. Robbins found the whale floating with its back at the surface, she initially thought the creature was merely resting. But as she got closer, she saw the rope, the shark, and the whale’s bloodied dorsal fin.

“Because of the entanglement, the whale was unable to move normally, and was likely quite limited as to how it could thwart the shark,” she said in an e-mail.

To ensure staff safety from the approximately 15-foot shark, the center’s Marine Animal Entanglement Response team began the disentanglement operation from aboard its 35-foot response vessel, Ibis, named after the first whale the organization freed in 1984.

The team used a hook-shaped knife connected to a long pole to cut the rope from the mouth of the whale. That allowed the creature, which was curled in the shape of the letter “C,” to correct its posture.

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Video of the entangled whale:

After the whale was able to return to a normal horizontal position, the shark lost interest and swam away, said Scott Landry, director of the Marine Animal Entanglement Response team.

The team deployed a small inflatable boat to finish the disentanglement. Using a work rope affixed to the whale’s entangled tail, the team was able to pull up to the mammal as it towed the inflatable boat behind. The team made a series of cuts that freed the tail, and the whale immediately swam out of the area.

“This whale is very lucky,” Landry said. “It probably would have been killed by the shark if we had not freed it.”

The team has saved more than 200 sea creatures since 1984. But Saturday was “the first time in history [the team] was accompanied by a white shark,” Landry added.

The humpback whale was the sixth whale to be freed out of 11 entanglements the center has identified this year. Of the 1,000 whales on the Gulf of Maine, which stretches from Cape Cod to Canada, 10 to 12 percent get entangled each year, Landry said.

The response team freed a minke whale on July 5, about 40 miles off Martha’s Vineyard. In late April, the team disentangled a whale with “a perfect collar of rope” around its neck, Landry said.

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Spinnaker, an 11-year-old young adult female whale, was found dead one week after being freed from ropes in May, Landry said.

“Hopefully we’re going to see this whale mend,” he said. “But even after disentangling a whale, it’s not guaranteed to survive.”

Entanglement, Landry said, is one of the biggest threats facing whales today.

“Wherever you have rope and whales overlapping, that’s where the problem is,” he said.

New regulations reduce the number of buoy lines fishermen can use. The National Marine Fisheries Service is investigating the source of the ropes that ensnared the young whale; Landry said they were probably part of fishing gear.

Now that boating season is underway, Landry urges mariners to report any entanglement sightings of whales, sea turtles, and other marine animals to the Coast Guard or the Marine Animal Entanglement Response Hotline at 1-800-900-3622 .

Boaters should not attempt to disentangle animals on their own, and should stand by the animal at a safe distance until trained responders arrive, he said.

Video of the shark:


Rosa Nguyen can be reached at rosa.nguyen@globe.com.