ROCKPORT — Front Beach patrons spotted a shark toward the northwestern-most part of the beach before a lifeguard was on duty yesterday.
But the town did not need to hire a grizzled captain to hunt the fish down. It left the beach — and beachgoers — unharmed — and experts said they believed it was a species that does not pose a threat to swimmers in the first place.
Tourists and beachgoers said they first spotted the fish around 8:45 a.m., and it stayed close to shore for about half an hour before heading back out.
The species of shark was unclear, but from pictures of the dorsal and tail fins poking above the water, some guessed that it was a basking shark, which feeds off plankton, while others thought it could be a blue shark, which eats fish.
Beachgoers also gave varying descriptions of the shark’s size, estimating it was between 3 and 6 feet long.
Jeff Archambault, 40, was visiting from Rhode Island yesterday when he saw the fish. Archambault said the beach was sparsely populated at the time, and the sighting did not spark a panic or emergency.
“A bunch of people took pictures,” he said.
Tony LaCasse, a spokesman for the New England Aquarium in Boston, said it was most likely a blue shark.
While potentially deadly great white sharks have been seen again this summer off Cape Cod, blue sharks are not a significant threat to swimmers, and they are most commonly seen in July, August and September, he said.
“Literally, 90 percent of the sharks (seen) on the North Shore are blue sharks,” La-Casse said.
Basking sharks, which eat plankton, are some of the largest fish in the ocean, growing up to 20 feet; newborns are typically 41/2 feet long. While they do stick closer to shore to catch plankton and other prey, LaCasse said the basking shark is a slow mover compared to carnivorous sharks.
When catching food, “they look like they the mouth of an old Studebaker,” LaCasse said.
The shark off Rockport yesterday reportedly swam within 30 to 40 feet of the shore, according to witnesses, while others said it swam between the shore and the small square dock that lies off Front Beach.
“It was pretty cool coming after Shark Week,” said 37-year-old Bridget Hammond, visiting from western Massachusetts.
“Shark Week” is an annual summer feature on the Discovery Channel in the summer, with sharks featured in programming for the entire week; it ended Sunday.
One 62-year-old Rockporter who has lived across Front Beach for years said she had never before seen a shark.
“It was exciting,” Laurel Juthe said.