Condensed sumary of imgur comments: since dolphins have actual eyes, why is the sonar needed in order to see the ninja turtle?

This is really cool!

Right??

According to Whale Facts,

The quality of eyesight a dolphin has often depends on its species.

While many species of dolphin are known for their excellent eyesight there are some species that have poor or limited eyesight where they can only see short distances or objects that are very close in proximity.

A few species such as the amazon river dolphin can only make out certain distinctions of light variations and shapes that are within a few feet in front of them making these marine mammals essentially blind.

http://www.whalefacts.org/can-dolphins-see/

Fascinating but I'm still not sure why they need eyes AND echolocation.

Today I learned that dolphins sleep with one eye open at all times:

http://animals.mom.me/dolphins-eyesight-4144.html