Story highlights FBI investigates why Tien Phuoc Nguyen, vacationing with family, jumped off cruise ship

Adventure of the Seas was about 15 miles east of Mona Island, Puerto Rico

Nguyen went overboard near the end of a weeklong cruise

The U.S. Coast Guard is searching off the coast of Puerto Rico for a Canadian who witnesses say jumped off a cruise ship Saturday night.

The FBI is investigating why Tien Phuoc Nguyen, 26, jumped overboard while on a cruise with his family, a Coast Guard news release said Sunday.

Adventure of the Seas, a Royal Caribbean International cruise ship, was about 15 miles east of Mona Island, Puerto Rico, when Nguyen jumped into the water, the Coast Guard said.

A Coast Guard MH-65 Dolphin helicopter and the Coast Guard Cutter Cushing were sent to the area to search late Saturday.

The cruise ship, which was sailing to San Juan, immediately turned around to search for the missing passenger, a statement from Royal Caribbean International said.

"A review of the ship's closed-circuit camera footage observed the guest going overboard," the cruise line said. "The location of the ship at the time the guest went overboard was marked on the ship's Global Positioning System and the ship, along with the Coast Guard, conducted a search for the missing guest."

The cruise to San Juan resumed Sunday morning, leaving the search to the Coast Guard, the statement said.

The Adventure of the Seas was near the end of a weeklong cruise that began in San Juan.