A Deep Dive into the world of an Elephant seal

A Deep Dive into the world of an Elephant seal

I want you to think back to exactly where you were and what you were doing two and half hours ago. Then I want you to image that you took a deep breath and filled your lungs all the way with air and that you have kept that air inside your lungs for two and a half hours. Finally you exhale.  That is how long a northern elephant seal can hold its breath.

Northern elephant seals (Mirounga angustirostris) are the deepest diving marine mammal and they can routinely
dive to over 5,000 feet or about a mile down into water holding their breath for upwards of two hours.

One thing that I have always wondered about is how these animals can survive under these extreme conditions?
This is the critical question that sparked my interest in physiology, or the study of how their bodies work.

In this post, we are going to explore some of the strangest adaptations of these deep diving
Northern elephant seals.

If you have ever swam in a pool you know that when you dive you need to inhale completely
and hold that air within your lungs.  It turns out, that when elephant seals dive they do the complete
opposite. Just before diving, they exhale all of the air out of their lungs and for the first twenty
minutes of their dive they use oxygen already stored in their blood and muscles to survive

(Longstreth, 2016).

Northern elephant seals also have another mind blowing adaptation for deep diving.

Due to the fact that they only have a limited amount of oxygen that can be held within their

blood, they need to actively conserve as much oxygen as possible while they dive.

A way that they do this is by lowering their heart rate.  The normal resting heart rate for

an elephant seal is about 64 beats per minute. This is even lower than an average resting

heart rate of a human female. According to the American Heart Association(AHA) a

female’s resting heart rate is between 70 and 100 beats per minute. When elephant seals dive

their heart rate can drop as low as THREE beats per minute (Andrews, 1997).  Here is an

informative graph showing how their heart rate changes as they dive. For example, when

this adult female elephant seal dove to about 450 meters her heart rate dropped to about

five beats per minute. If a human heart rate dropped to five beats per minute we would

not be able to circulate enough blood through our body and we would die.

Time of Day

By lowering their heart rates and only relying on oxygen storage in their blood and muscles,

these animals can dive to incredible depths. They have specialized proteins called myoglobin

in their blood and muscles that bind oxygen. This is similar to what hemoglobin does in our blood.

These repetitive, long dives have remained a physiological mystery. It appears that the oxygen

stores in their blood alone is insufficient to maintain their metabolism while they are diving

(Meir, 2009).  This is still a heavily researched area of study because scientists are still unclear

how they can survive with such little oxygen in their bodies.

We also know that the more blood volume the animal has, the more oxygen that they can store.

The graph below shows that there is a direct relationship between the weight of a female

northern elephant seals and how much oxygen their body can store while they dive.

We might know a great deal about how deep these animals dive, but it still somewhat of a

mystery of where they go when they leave the beaches. Dr. Patrick Robinson and his

team from UC Santa Cruz is looking to answer this question by attaching geographic

location tags and time-depth recorders to female northern elephant seals. These tags

will record data about how deep they dive and where they go while we can’t physically

see them. Here is a picture of a time depth recorder that gets deployed on a Northern Elephant Seals.

Through this incredible technology, we have discovered that northern elephant seals are not

only the deepest diving marine mammal but they travel incredibly far distances in short periods

of time. In only 234 days a tagged female northern elephant seal swam OVER 7,580 miles

(Stewart 1995).  This is equivalent to the distance between San Luis Obispo, California and

Cairo, Egypt.

Believe it or not some seals have been recorded to swim farther than that. The picture below shows

four tagged female northern elephant seals and where they traveled during their long migrations.

Each color represents a different female northern elephant seal tagged at Año Nuevo State Park

here in California.

The study of northern elephant seals is intrinsically entwined with the development of new

and innovative technology. They are a beautiful but extremely complicated organism to study

because they spend 90 percent of their time out at sea thousands of miles off the coast where

researchers can’t go to observe them (Hassrick, 2010).  Just like their incredible adaptations,

with changing technology researchers have adapted they way that we study these animals.

References:

Longstreth, C. (2016). "The northern elephant seal: the biochemistry of this marine mammal may hold clues to better human health." Natural History: 14.

Andrews, R.D., et al. (1997). "Heart rates of northern elephant seals diving at sea and resting on the beach." Journal of Experimental Biology: vol. 200, no. 15 p. 2083.

Stewart, B. & R. DeLong, (1995). Double Migrations of the Northern Elephant Seal, Mirounga angustirostris. Journal of Mammalogy: 76(1), 196-205.

Meir, J. (2009). Extreme hypoxemic tolerance and blood oxygen depletion in diving elephant seals. American Journal of Physiology., 297(4), R927.

Hassrick, J. (2010). Condition and mass impact oxygen stores and dive duration in adult female northern elephant seals. Journal of Experimental Biology., 213(4), 585.