Lots of money.
Shoot the fish, grab the treasure. Get the biggest stash you can and buy upgrades in the shop to help you progress! Catch fish as many as you can before time runs out.
Use X and Z to move ya boat.
Use left and right arrows to aim ya harpoon.
Press space to spear something valuable.
Spend cash in the shop and upgrade ya gear.
Drop deapth charges with the ENTER key.
Keep an eye on yer timer.