Full list of all 12 Ecco the Dolphin achievements worth 200 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
Complete the game 2 times.
You have completed the game without dying more than 3 times.
You reached Ridge Water without dying.
You passed the Undercaves without being hit by any Octopus.
You passed the Undercaves without dying once.
You killed 30 enemies with the Death Sonar.
You acquired the Death Sonar.
You reached the Dark Water Level without acquiring the Death Sonar.
You found the hidden glyph in Origin Beach.
You found the 'Find Big Blue' glyph in Island Zone.
You killed 10 Sharks in a row.
You rescued the dolphin family in The Lagoon level.