Apollo the harbor seal shimmied out of the Riverhead Foundation’s wooden crate and into Shinnecock Bay on Sunday as more than 100 onlookers wrapped in winter garb applauded.

“He walked like a caterpillar,” said Jordan Schule, 12 of Wading River.

“It was awesome!” said her 10-year-old sister Jenna.

The 70-pound, 3-foot-long harbor seal was found on Dec. 23 in Montauk with ear and respiratory infections, said Rob DiGiovanni, executive director and senior biologist of the Riverhead Foundation, which rehabilitated the seal.

While the human spectators hid their faces from the biting wind whipping sand beneath the Ponquogue Bridge, Apollo and other seals are well-suited to the cold, DiGiovanni said. They spend their summers in the chilly waters off Maine and Nova Scotia and can be seen lolling about Long Island from late fall through late spring in increasing numbers.

DiGiovanni said ten or 15 years ago, he would do aerial counts along the shores and see only a handful of the marine mammals. Now they count hundreds from the air, a resurgence he attributed to protection of the seals under federal law since the 1970s. The group rescues and releases about 100 seals a year, he said.

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With a GPS tracker attached to Apollo’s back, like a strapped on cellphone, scientists with the Riverhead Foundation hope to follow Apollo’s path. DiGiovanni said he expectshim to head north.

Ares, another seal released by the nonprofit group in January, has hung around the South Shore of Long Island but is currently off Montauk.

A map and locator of Apollo’s position should be on the group’s website in a couple of days, DiGiovanni said, at http://www.riverheadfoundation.org/tracking-maps/

He said if you spot a seal, stay 50 yards away and call the Riverhead Foundation’s emergency hotline at (631) 369-9840. Even though most seals won’t need to be rescued, he said the group would rather have too many calls than too few.

On Sunday volunteers took the seal in his crate around the chained off area to show the onlookers. After depositing him about 20 yards up on the sand, Apollo peaked out and then made his way down. In all, it took a few minutes before he ducked under the water.

Despite the unseasonable wind and cold, the crowd clapped through their gloves and gave a cheer when he made it.

“It was actually pretty exciting,” said Kevin Vonthaden, 46 of Manorville. “I’d do it again, on a warmer day.”