Among small- to medium-sized marine mammals such as seals and dolphins, the longer an animal can stay submerged during a dive, the greater the depth the animal can reach
Dolphins can dive to greater depths than northern fur seals can, and elephant seals can stay submerged longer than Weddell seals can
Weddell seals can dive to greater depths than dolphins can and can stay submerged longer than northern fur seals can.