I thought Jaws 2 was Jaws 1 Junior. When Jaws is shot in the gob by the copper at the end of 1 and explodes, Jaws Junior falls out and is ready for revenge.
Jaws numbering follows the logic of page sizes. Just as A1 is twice the size of A2, which is twice the size of A3, which is twice the size of A4 and so on, the Jaws shark with the lowest number is the oldest and hugest, Jaws 2 is half its size, etc.
Not sure why these decisions were made, but in those days everyone was a bit mad about photocopiers so the sizing issue of paper reams presumably bled into their subconscious somehow. I'm glad. Without Xerox we probably wouldn't have had 101 Dalmations.