Deep Divers

Another Lens on Life post by Chuck Kopczak, PhD

A young male northern elephant seal lies in waves as the early morning sun lights up the beach.
Chuck Kopczak, PhD

A young male northern elephant seal (Mirounga angustirostris) lies in waves as the early morning sun lights up the beach.

Today’s photo was taken at Piedras Blancas on the California coast with a Canon EF100-400 mm f/4.5-5.6L lens zoomed to 400 mm on a Canon EOS 5D Mk. III. The exposure was set to 1/250 sec at f/6.3 and ISO 800.

Besides being enormous in size, the northern elephant seal (Mirounga angustirostris) also has enormous abilities when it comes to diving to great depths in search of food. In fact, among mammals, the depths to which they can dive, and the time spent holding their breath is only exceeded by the sperm whale (Physeter microcephalus).

Found along the Pacific coast of North America from the Aleutian Islands to Baja California, when northern elephant seals aren’t hanging out on the beach to either mate or molt (shedding dead skin and hair all in one big yearly event), they are out at sea feeding to get ready for those events. Research has shown that while at sea, northern elephant seals literally spend almost all their time below the surface holding their breath, which helps to explain the mystery of where northern elephant seals went when they went to sea. Diving nearly continuously for the six to eight months they spend at sea, they can reach depths of 1,000-2,500 feet (330-800 m) for 20-30-minute intervals with only short breaks of only a few minutes at the surface. The deepest dive recorded for a northern elephant seal was to 5,015 feet (1,540 m) with a duration of nearly two hours.

These prodigious diving skills are made possible in part by adaptations that allow the animals to tolerate low oxygen conditions that would result in death for humans and many other air-breathing species. By having increased oxygen storage capacity, managing the depletion of those stores, and having increased tolerance to extremely low levels of oxygen in their blood stream, northern elephant seals can spend almost all their time at sea underwater holding their breath.

Northern elephant seals store many times the amount of oxygen in their blood stream and muscles as humans can. And while we try to increase the amount of air we hold in our lungs while diving, northern elephant seals exhale at the start of a dive, and soon after leaving the surface, the pressure of the surrounding water completely collapses their lungs, forcing out any remaining air. Fortunately, the fluid coating the interior of their lungs is specialized allowing their lungs to re-inflate upon return to the surface.

The northern elephant seal clearly deserves its reputation as a world class deep diver.