The whale was big. But what amazed Cheshire Rhett was the size of its tail — as wide as the boat was long.

Humpback whales

Grow to 60 feet long, weigh more than 40 tons.More than 11,000 estimated in the North Atlantic; more than 500 in the Gulf of Maine stock.Trap prey in bubble clouds; occasionally “bubble net,” blowing bubbles in circular patterns to herd fish, a behavior unique to humpbacks.Frequently breach and slap the surface with their fins.Males sing complex songs on wintering grounds in Hawaii that can last up to 20 minutes and be heard for 20 miles.National Marine Fisheries Service

Huge flapping flukes are a signature of a humpback whale, along with pectoral fins so long they look like wings. Rhett was among a group of anglers surprised Sunday by a 40-foot-plus humpback just off the Charleston jetties, close enough to Morris Island that you could see land.

“It was a unique experience,” said Rhett, 58.

He has been fishing offshore all his life but never had seen anything bigger than a pilot whale, less than half the size.

The anglers were aboard a 25-foot boat returning from a day’s fishing. They didn’t spot the whale at first. They spotted 40 or more bottlenose dolphins that were feeding around it in a swarm.

Humpbacks aren’t the rarity that the critically endangered right whales are. An estimated 11,000 humpbacks can be found in the North Atlantic; more than 500 are part of the Gulf of Maine stock, according to the federal National Marine Fisheries Service.

But they are just as enormous. They can grow as long as 60 feet and weigh more than 40 tons.

The whales are just one more impressive critter swimming off the Lowcountry this time of year, along with right whales, great white sharks and others.

A right whale survey flight spotted a pair of humpbacks off Murrells Inlet two weeks ago, said Melanie White, the survey team leader for Sea to Shore Alliance. “That’s awesome,” she said, to spot one so close to shore.

Two radio-tagged great whites that are offshore, Mary Lee and Genie, pinged most recently off the Savannnah River.

Humpbacks seen offshore here are thought to be on their way on their way to wintering and calving grounds off the Dominican Republic. Right whales, too, migrate through the Lowcountry or hang around to calve. The waters off the Southeast coast from here to Florida are considered their breeding grounds.

Already this year, right whales have been spotted in offshore waters from just south of Charleston to Hilton Head, White said.

The anglers off the jetties put their boat in idle and watched for about 10 minutes as the whale dove and surfaced, surrounded by the stream of dolphins. At one point it swam straight toward the boat, getting within 20 yards or so before diving.

They won’t forget the spectacle. Boat owner David Swanson kidded Rhett that he is thinking about starting a whale watching tour.

Reach Bo Petersen at 937-5744 or @bopete on Twitter.