The different levels on Steemit are:
Redfish/plankton <500 SP
Minnow 500-5000 SP
Dolphin 5000-50,000 SP (I think? Not sure about the upper numbers)
Orca 50,000-500,000 SP
Whale 500,000 SP+

essentially. It's really measured in Vests, but Steem Power is the easier approximation of Vests. The number of Vests you have is the number beneath your little fishie icon when you click on your Steemit Board notifications to see your badges.