VIDEO: Killer whale seen swimming off Cape Cod

CHATHAM, Mass. — It was an amazing encounter for men fishing off of Chatham - and one they're likely never have again.

"We were just harpooning tuna fish, looking for tuna fish, and I saw this tall dorsal fin," said Greg Gibbs.

It was an orca swimming alongside their boat.

"You don't see that, it's a once in a lifetime thing," said Charlie Whitcomb.

The men were about 50 miles east of Chatham at the time.

"It came up behind us and came alongside us and gave us a pretty good show. It was breathtaking," said Kelly Zimmerman.

Gibbs shot video of their encounter.

Chatham-whale-sighting-vid Chatham-whale-sighting-vid

"When we first saw him, me and Charlie thought he was going after one of the porpoises but he was just swimming right behind the five of them," said Gibbs.

The whale kept them company for about 20 minutes.

"We were in a 36-foot vessel and it was almost as long as the vessel," said Zimmerman.

Orcas, also known as killer whales, are rare off Cape Cod, but not unheard of.

In 2016, an orca named Old Thom was spotted off Chatham.

>> Previous: Orca spotted off Chatham

The whale seen Monday is a male, according to Dr. Bob Kenney, a marine research scientist with the University of Rhode Island, and roughly the same size as Old Thom, but he couldn't confirm it's the same whale.

Whether he has been here before or not, the men say they're thrilled they witnessed his visit.

"I mean, we saw hundreds of whales in the morning, humpbacks, finbacks, minke whales, thousands of porpoise, but just to see one orca, it's awesome. It's a really cool thing to see."

Orcas are apex predators. Even great white sharks are their prey. Many on social media were asking if they would feast on the sharks and seals seen off the Cape. Experts tell us at the moment, this one is too far offshore for that.

>> Related: 'An invisible fence for sharks': New proposal to keep Cape beaches safer

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