Death Sonar Achievement in Ecco the Dolphin
Acquire the Death Sonar.
How to unlock Death Sonar
In The Vents level you will find a dolphin at the start that if you talk to him, he will ask you to find 3 of his missing pod members. Find them, bring them back and the achievement is yours. If your having trouble, the link below is a map that has the mission dolphin marked as a BLACK square and the lost pod members as WHITE squares.(Thank to www.ecco-darksea.com for the maps.)