Even though it's a mammal and not a fish, the Weddell seal of the Antarctic is one of the greatest deep-sea divers in the world. Weighing up to 1,200 pounds, the Weddell seal can cruise under water for up to 70 minutes. It is able to reach depths as great as 1,600 feet. For comparison, the record for a human being is a 13-minute, 43-second dive down to 282 feet.