A species of shark not often seen in New England is becoming an increasingly popular sight in the waters off Massachusetts. Smooth hammerhead sharks are being reported by fishermen and recreational boaters this summer.

State shark biologist John Chisholm told WBZ-TV that last weekend there were about a half-dozen sightings of hammerheads at the mouth of Buzzards Bay, west of Cuttyhunk Island. There have also been sporadic sightings off Martha's Vineyard and Nantucket.

"We've always been on kind of the northern limit of their range," Chisholm said. "But in the past several years with the water warming we've been seeing more and more, especially around the islands and south of the Cape where the water gets really warm during the summertime."

Other shark species could be headed for Massachusetts

And it's not just hammerheads that could be on the way to Massachusetts thanks to a warming ocean.

"I'm expecting we'll see some more southern species like the blacktip and spinner shark and maybe eventually the bull shark," Chisholm said.

Bull sharks are known to be the most aggressive toward humans. While shark attacks are rare, a 9-year-old girl in southwest Florida was seriously injured after being attacked in June by what's believed to have been a bull shark. 

What to know about smooth hammerheads

Smooth hammerheads, on the other hand, are nowhere near as dangerous to swimmers as bull sharks or the great white sharks that are already visiting Massachusetts for the summer.

"They're not really a threat to humans. they're a fish-eating shark," Chisholm said about hammerheads. "They're not really interested in people."

According to the ocean conservation organization , smooth hammerheads are on the larger end of the hammerhead species, with an average length of 8 to 11.5 feet. They can live up to 20 years or longer and can birth up to 53 pups at a time.

Chisholm said he doesn't believe there's been a fatal attack on a human by smooth hammerheads, but noted that they do have sharp teeth so people should still keep their distance. He encourages anyone who sees a shark to report the sighting.

"They're very distinct. It's easy once you get a good picture, you know you're not going to mistake a hammerhead compared to some other species that look very similar," he said.