Six seals were spotted in the waters off Centre Island on the North Shore on Sunday morning, a somewhat rare sighting that experts say is becoming a more common occurrence.

Bill Bleyer, a retired Newsday reporter and Bayville resident, snapped pictures of two of the seals about 10:30 a.m. at low tide from Rocky Point — just east of Centre Island Beach.

“It took like 15 minutes to hike a rocky, slippery beach, but it was worth it,” said Bleyer, 63, a year-round Bayville resident since he was 13. Bleyer said it was his first time seeing seals in the Bayville area.

Bleyer said he was about 100 yards away from the seals. One of the seals Bleyer photographed was perched high atop a rock, while another was swimming. The others appeared to be resting on low-lying rocks, he said.

“The one on the rock was checking me out,” said Bleyer.

Rob DiGiovanni, executive director and senior biologist at the Riverhead Foundation, which tracks the movements of seals and other sea life in and around Long Island, said seals have been more typically spotted on the East End. Giovanni attributed the abundance of seals, which mostly live in the colder waters off Maine, Nova Scotia and Massachusetts, to the 1972 Marine Mammal Protection Act, which prohibited the killing of seals.

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“It is becoming more of a common occurrence,” said DiGiovanni. “We’re starting to see seals in areas all over Long Island and seeing them in larger numbers. . . . It’s a positive thing that you’d want to see as a result of conservation efforts.”

DiGiovanni, who viewed Bleyer’s photographs, said they appeared to be “robust” harbor seals. Though seals enjoy the colder weather, Sunday’s milder climate was “not a deal breaker for them.”

“It’s a nice day, so you will see seals coming out,” he said.

The foundation, which takes a monthly census of area seals, spotted about 500 gray seals off Little Gull Island near Plum Island in March 2015.

DiGiovanni urged anyone who sees seals in the waters off Long Island to contact the foundation’s 24-hour hotline at 631-369-9829.