Back to the Shrine

  Ship
Used for navigating through the overworld and for bombing Jaws by pressing the B and A buttons for firing left or right, respectfully.
  Jaws Tracker
After getting 5 shells, go to harbor #2 to receive a tracker in exchange. The reason for it is to hear when you're close to Jaws, but it doesn't make too much sense why you would need one since you'll be able to see Jaws' dorsal fin when close. It's extrememly annoying AND pointless!
  Plane
Inbetween upgrading your ship and hunting down a man-eating shark, you'll go through bonus areas in a bombing plane. The more jellies you destroy, the more points awarded!

Now, I ask, where's the E.P.A. when you need them?
  Submarine
By far the coolest thing in the game, after obtaining 20 shells or power lvl 5, the sub will appear in one of two places. Either by harbor #1 (pictured in geography) or at the water directly behind harbor #2. It shoots missles, instead of spears, and moves along much smoother than the diver (equivalent to jelly fish.) When you get hit, you'll lose the sub but it'll reappear in either the two places from where you first got it (overworld).