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Beaches on the Cape and Nantucket close after at least a dozen shark sightings

The shark was spotted near Cisco Beach, prompting the harbormaster to declare the beaches closed for two hours.

Lifeguards Avery Stolte and Willem Steiner watched for sharks Saturday at Cisco Beach after the second closing of the day on Nantucket’s south coast beaches. Stan Grossfeld/Globe staff

Beaches on Cape Cod and Nantucket were peppered by at least a dozen shark sightings Saturday, leading to multiple closures in the late morning and afternoon, authorities said.

On the Cape, shark sightings were confirmed near Coast Guard Beach in Provincetown, Long Nook, High Head, and Ballston beaches in Truro, Marconi Beach in Wellfleet, and Nauset Beach in Orleans in the late morning and afternoon, according to the Atlantic White Shark Conservancy’s Sharktivity app.

Long Nook Beach was closed to swimming from 1:15 to 2:15 p.m., according to the app, citing town officials. Another sighting was listed on the app a short distance away.

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A spotter plane sighted sharks near Marconi Beach and Nauset Beach, prompting them to be closed to swimming until about noon, according to the Sharktivity app.

The conservancy confirmed the sighting of a great white shark near Nausetand also reported a second sighting there by a spotter pilot. A third sighting at Pochet, half a mile south of the beach, sparked another closure there from 2:45 to 3:45 p.m., according to the app.

A spotter pilot also sighted a great white about 50 yards off Ballston Beach in Truro. It was not clear whether two sightings near Coast Guard Beach and single sightings near High Head and Ballston beaches, all posted on Sharktivity in the afternoon, resulted in beach closures.

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Beaches on the south shore of Nantucket were temporarily closed to swimming after two confirmed shark sightings Saturday morning and afternoon, the Nantucket harbormaster posted on Twitter.

The first shark sighting was near Cisco Beach, prompting the harbormaster to declare the beaches closed for two hours, beginning just before 10 a.m. A second report of a shark around 1:30 p.m. on the south shore caused the beaches to be closed for an hour.

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“Please exercise extreme caution if visiting the south shore today,’’ the harbormaster said in a tweet. Those sightings were listed but not confirmed by the white shark conservancy.

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The sighting comes after a Martha’s Vineyard beach was temporarily closed for another shark sighting earlier in the week, among other such closures along the Cape.