The influx of large sharks, notably great whites, in the waters off of Cape Cod has been well-documented. An ever-growing seal population draws the great whites close to shore. Perhaps in an attempt to flee the sharks, or to find a less competitive area for food, seals are moving north, and are more regularly spotted off the coasts of places like Marshfield and Scituate.

This is the first in a two-part series focusing on sharks on the South Shore, including off the shores of Marshfield and Scituate.

It’s a perfect summer day on the South Shore and you’re kayaking up the North River. As you enjoy the sights and sounds of the natural world around you, from the corner of your eye you spot something race past you just below the surface of the murky water. Leaning curiously closer to the water with a bit of apprehension, you think for a moment about what you caught glimpse of – something that looked like a large seal. It is then that you sense a shift in the balance of things, and before anything has the chance to register in your mind you see it – a large dorsal fin moving gracefully through the water. With a mixture of awe and horror you watch as a large shark glides past you; a shark large enough to easily capsize your kayak and send you sprawling into the water – with it.

Such a scenario has not happened. Not yet. And quite possibly not ever. The idea of large predatory sharks following seals into the North or South rivers is not as far-fetched as it might seem, however.

“Seals are very common in the rivers; we typically see arbor seals,” said Sara Grady, watershed ecologist with the North & South Rivers Watershed Association. “Seals are seen every year, most often in the winter when the adults are hauled out on floats in the lower part of the North and South rivers and other protected areas in the region - Scituate Harbor, Green Harbor, plus the rocks along the coastline. They tend to travel further upstream in the spring, following the river herring, a major food source. In the summer, typically July, we start to see seal pups hauled out on our beaches while their mother is getting food.”

This year a seal was seen where the Third Herring Brook meets the North River, which is about 11-1/2 miles from the mouth of the rivers, Grady said.

“They would probably be willing to follow the food as far upstream as they could.”

Following the seals are the sharks.

The influx of large sharks, notably great whites, in the waters off of Cape Cod has been well-documented. An ever-growing seal population draws the great whites close to shore. Perhaps in an attempt to flee the sharks, or to find a less competitive area for food, seals are moving north, and are more regularly spotted off the coasts of places like Marshfield and Scituate.

Andrew White, an avid South Shore fisherman and boater said as of July 16 he has not seen any seals in his travels, which includes both the North and South rivers as well as into Humarock and as far north as Egypt Beach.

"I think with warmer water, August and September, it’s possible for seal activity to be followed by some sharks," he said.

White was on Nantucket last week, however, and saw seals on both sides of the island.

Ben Haskell, acting superintendent of Stellwagen Bank National Marine Sanctuary – with headquarters located in Scituate - has seen an increase in mostly grey seals in the Sanctuary.

Stellwagen Bank National Marine Sanctuary encompasses a total of 638 square nautical miles, or 842 square miles. The western boundary line of the sanctuary is approximately 25 miles east of Boston; the southern boundary is three miles from Provincetown while the northwestern boundary is three miles from Gloucester.

Grey seals are bigger than harbor seals and are a main food source for great white sharks.

“Almost every time I go out there now I see at least one or more popping its head up and checking us out,” he said. “They’re starting to move up from the Cape into the Sanctuary area, and presumably along the coast. We see them all year round but mostly in the warmer weather. They like to eat mollusks and shellfish and are known to raid lobster traps. They’re curious but not aggressive.”

Marshfield Harbormaster Mike DiMeo has also noticed an increase in grey seals in the area. And as for seals in the North River, he said a harbor seal was recently seen as far up as the Union Street Bridge.

DiMeo and his department are working with the Atlantic Great White Conservancy to initiate a seal tracking protocol.

The mission of the Atlantic Great White Conservancy, a non-profit organization based out of Chatham, is to support scientific research, improve public safety, and educate the community, to inspire conservation of Atlantic white sharks.

“Where there are seals there are usually sharks,” DiMeo said. “I do think it’s plausible a large shark could swim up the North River.”

Check next week's Mariner for Part 2 of the story - sharks. In the meantime keep up with the sharks around Massachusetts with this Twitter link.



A Twitter List by WickedLocal

Follow Ruth Thompson on Twitter @scituateruth.