Monday morning had already been good to Bruce Peters. By 8:45 a.m., the commercial fisherman, who had taken some customers out on a routine fishing trip off Cape Cod around 4 a.m., had already seen 50 to 60 whales and dozens of dolphins.
“It was like Sea World out there,” said the 60-year-old fisherman, who has been on the water most of his life.
So when a customer announced that there was an orca prowling the waters near their tuna fishing boat, Peters didn’t believe him. After all, orcas, commonly known as killer whales, are exceedingly rare in this part of the Atlantic; marine experts said they can’t remember ever seeing one this close to Cape Cod. They can’t even estimate how many orcas live in the northwest Atlantic, because there just aren’t enough sightings.
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But sure enough, it was an orca’s 6-foot slick black dorsal fin cutting through the water about 13 miles northeast of Chatham.
Peters, owner of Capeshores Charters. snapped a photo, which he posted to Facebook and which quickly attracted the attention of amateur wildlife lovers and veteran marine biologists alike. Tony LaCasse, a spokesman for the New England Aquarium, said the aquarium’s researchers conferred with Dr. Jack Lawson, a marine mammal researcher at the Canadian Department of Fisheries and Oceans, and confirmed that it was an orca — and in fact, one they’ve seen before.
This particular orca is affectionately known as “Old Thom,” a male who is about 30 feet long and weighs eight tons, age unknown. And he’s known for being spotted in unusual places. He has been sighted by researchers in 2014 and 2015 in the Bay of Fundy, off Nova Scotia, still farther south than orcas’ typical roaming waters near Newfoundland and Labrador. In fact, LaCasse said, Old Thom has never been seen in those typical areas.
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So while seeing an orca off Cape Cod is highly unusual, seeing Old Thom in particular there is not so much.
“It’s really hard to know why one animal does anything. You’ll see a pattern of behavior, but then there are other individuals, that’s just not what they do,” New England Aquarium research scientist Philip Hamilton said. “Maybe that’s how he was raised. We don’t know all the things that go into where a whale goes and why.”
It’s possible that other orcas also travel this far south — but sightings are so rare, Hamilton said, there’s no way of knowing.
“We just haven’t had the opportunity to see that,” he said.
Peters said he has only ever seen one other orca in his career, and that was off the coast of San Francisco. For a fisherman who sees humpback and minke whales regularly, this sighting was a reminder of what makes his job so special.
“I’m grateful to have the job that I have. People pay me to take them out there to see something like that,” he said. “It was thrilling but mostly humbling to be blessed to see.”
There was one downside, though: With the killer mammal circling his boat, even swimming alongside it for a bit, he didn’t catch a single tuna.
Cape Cod residents on social media have been hopeful Old Thom will have the same effect on the plentiful seals that crowd their beaches. But LaCasse said they will probably be disappointed, as the orca population Old Thom comes from has never been documented to eat seals.
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And as for those hoping for an epic showdown between local great white sharks and this deadly predator?
“Maybe on the fantasy channel,” Hamilton laughed.
Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.