What am I?

Cover the clues so you can only see number one. How many clues do you need before you know the answer?

1. I would rather still be in the sea.
2. They found me in the Bay of Islands.
3. I am part of something much bigger.
4. Catch me and you will see two.
5. If caught, I would rather stay in one piece and be tagged and returned to the sea.

Answer in next week's TreasureLink.