There is a known bug with the quests that ask you to find and turn in 5-6 pieces of litter. The quest log contains no clues on where to find them, and Ranger Bear doesn't give any hints on finding them.
Unfortunately, the pieces of litter aren't even spawned on the island, so you won't be able to complete this quest. On the positive side, timed quests will randomly come around again and don't have any critical rewards, so you're not missing out on anything major.
This bug is in fixed in version 1.8.0