There are sharks in Duxbury Bay — a lot of them.

So many, in fact, that Duxbury Bay has been recognized by the federal government as the largest sand tiger shark nursery north of Delaware Bay, according to John Chisholm, a biologist with the Massachusetts Division of Marine Fisheries.

Chisholm has been studying sand tiger sharks for four years in Duxbury, Kingston and Plymouth Bays, and he presented his findings Sunday to a rapt audience at the Duxbury Bay Maritime School. The discussion was sponsored by the Duxbury Beach Preservation Society Newborn sand tiger sharks and juveniles up to two years old are plentiful in Duxbury Bay, said Chisholm. He estimated that there are as many as 100 of these sharks in local waters during the summer. The grayish-brown sharks are born live in March and April in the mid-Atlantic and then find their way north to Duxbury.

Young sand tiger sharks measure between 3 - 5 feet long and they like to hang out in the Back River during high tide and in pockets of deeper water off Duxbury Beach during low tide, according to Chis-

holm. Adults can grow to 10 feet long, but Chisholm said scientists have not seen adult sand tiger sharks in Massachusetts in many years.

Despite having a jaw full of large, needlelike teeth, sand tiger sharks pose no threat to people, said Chisholm.

“These sharks are not dangerous to people,” he said. “They are fish eaters. They have zero interest in people.”

And people, it seems, are not aware they are swimming and clamming in the bay right next to the baby sharks.

“We’ve caught them in between swimmers and in between quahoggers,” said Chis-

holm.

Young sand tiger sharks may not be interested in people but they love the bait fish Menhaden, also known as pogies, which can be abundant in Duxbury waters.

“They’re like candy to them,” Chisholm said. He has caught 300 sand tiger sharks over the past few years and all but seven were caught using pogies.

The sand tiger sharks follow the pogies and swim into Duxbury Bay in mid- to late June and remain until early October. They leave and swim south to North Carolina when the water temperature drops below 60 degrees, said Chis-holm.

Chisholm and his assistants have been following the behavior of sand tiger sharks by using acoustic tracking devices. They catch the sharks – most often off the Powder Point Bridge – and insert a little black plastic tube about three inches long into their undersides. After stitching up the incision, Chisholm releases the shark. The acoustic “tag” transmits the individual shark’s whereabouts every time it swims past a receiver located in various parts of the bay.

Chisholm has discovered that these baby sharks don’t move too far and they stay in their own groups.

“The Duxbury sharks don’t go into Kingston and the Kingston sharks don’t go into Duxbury,” he said. The sharks don’t seem to like Plymouth Bay very much, he added.

While sand tiger sharks are found in other local waters, such as Quincy, they are much more abundant in Duxbury and Kingston, probably because of the water quality, said Chisholm. The oyster fisheries in the bay have contributed to improving the water quality as have the shared septic systems in Snug Harbor and Bay Road and the ongoing coastal pollution remediation projects.

Sand tiger sharks are protected by both the state and federal governments and killing them is prohibited.

Finding these sharks in Duxbury recently was a surprise, said Chisholm, because despite being very common in Massachusetts years ago, a commercial fishery exterminated most sand tiger sharks. He showed historical photos of fishermen and their multiple shark kills. From June to Sept. in 1918, over 1,900 sharks were killed, said Chisholm, for their shark liver oil.

“We haven’t seen an adult sand tiger shark in Massachusetts waters for decades,” he said.

Chisholm, who grew up in Plymouth, said he always wanted to be a shark biologist. He told the 50 children at the meeting that “we have the coolest sharks in our own backyard.”

In addition to the young tiger sand sharks, Chisholm said the most common shark found locally is the spiny dogfish. This slate gray to brownish gray shark has a spine on its dorsal fine and can grow to a maximum of 4.5 feet. Fishermen find them to be a nuisance as they get caught in lines and nets.

Also common are smooth dogfish, which have no dorsal fin spine and no teeth. They are usually three feet in length and like to eat crabs.

Chisholm said he has also seen brown sharks locally. These are bigger sharks – up to eight feet – with a big dorsal fin. They are not usually found as far north as Duxbury, so anyone sighting a brown shark is asked to call the Massachusetts Shark Research Program at 506-910-6329.

As part of the research program each summer, Chis-

holm keeps a sand tiger shark in a tank at Jones River Landing off Landing Road in Kingston. He said the public is welcome to view the shark to get a close-up look at a live sand tiger shark.