First you must collect the 8 Mission Shells scattered around the map to unlock each of the 8 Basic Missions. After completing the first 8 missions, you unlock the Super Mission. If you die then any incomplete mission progress will be reset, so you have to finish any given mission within one life. All completed missions and shells found will remain though.
Hammerhead Shark Missions:
3-1 Eat 40 Crabs
3-2 Eat 30 Sardines Within A Minute
3-3 Eat 5 Sting Rays
3-4 Swim 1000M Without Getting Stung
3-5 Eat 200 Fish
3-6 Find 3 Sunken Objects
3-7 Survive For 8 Minutes
3-8 Eat 20 Enemy Sharks
3-9 Score Over 100,000 Points
Mission & Treasure Map 3:
For more game tips, see:
http://www.urgametips.com/2013/04/hungry-shark-evolution-faq... and my solution for Super Mission 1: