Tuesday, February 2, 2010

Año Nuevo Elephant Seals

[Originally posted to MBA Student Oceanography Club (SOC)]

Elephant seals are amazing creatures.  It is easy to see them on the shore and imagine that they are slow and lazy.  Other than the brief brush ups among the males (see the video above), they didn’t seem to do much when we were visiting, but in reality they are well adapted for an extreme lifestyle.

For example, though they appear to laze on the beach for months at a time, they do so without eating or drinking any food or water.  Males can be on the beach for as long as three months, and may lose up to a third of their body weight during that time.  To make up for that lost weight,  elephant seals must be voracious and efficient eaters, so when it comes time to head to sea, they go right to the best fishing ground – in the middle of the Pacific north of Hawaii for females, and up near the Aleutian Islands for males – where they gorge on squid and fish.  The seals return to our coast twice a year, and may cover well over 10,000 miles in a year.

Each year they’ll spend 8-10 months at sea, 90% of which they are underwater.  They dive continuously, rarely spending more than five minutes at the surface between dives.  They even dive while sleeping, taking 15-30 minute naps without breathing.  While foraging, they can dive for almost two hours at a time, and reach depths of nearly a mile.  At those depths, the pressure is tremendous; any air in their lungs would quickly dissolve into their blood, causing major problems as it turned back into gas when they resurfaced.  To solve that problem, they actually exhale, completely emptying their lungs, before they dive.

Without air in their lungs, they have a host of other physiological adaptations that help ensure that they have enough oxygen so that they don’t pass out while they are under water.  For one, they have blood extremely rich in hemoglobin, the protein that binds oxygen and gives blood its red color.  Similar proteins in their muscles allow them to stock their tissues with large amounts of oxygen.   When diving, they also lower their metabolism, slowing their heart rate and stopping blood flow to the skin to reduce oxygen consumption.

With such intense feats of swimming and diving, it's no wonder that they like to relax when they come to shore. 

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