This is Tingle’s island. He’s always found here after you free him from his cell at Windfall Island (D2). Come to this island after you find a new Triforce Chart and have Tingle decipher it for 398 Rupees.
Blue ChuChu
Defeat the Blue ChuChu near the small wooden sign for a Blue Chu Jelly.
Silver Rupee (via Treasure Chart #10)
Find and open Treasure Chart #10 (at Crescent Moon Island [E1]) to pull a chest from the Great Sea near Tingle Island. The chest contains a Silver Rupee.
Piece of Heart #16 (via Big Octo #2)
This sector has a 12-eyed Big Octo. Sail toward the flock of circling seagulls to find it, and then use the Boomerang to target up to five of its large, yellow eyes at once. When 12 eyes turn blue, the defeated Big Octo leaves behind a ring of light. Use the Grappling Hook to haul up a chest containing Piece of Heart #16.