Events at Sea

Swimming

Since elephant seals spend approximately 80% of their lives at sea, swimming and diving are hugely important and necessary skills

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Despite their bulk, elephant seals can swim laterally up to speeds of between 10 and 12 m.p.h. By keeping their back flippers together and moving them in a side to side motion with the aid of their powerful hip muscles, they can propel themselves quickly through the water. When swimming at speed, their fore-flippers are usually held close to their bodies to aid in their streamlining. In other instances, the fore-flippers can be used to aid in quickly changing directions, pushing past or over rocks, or fending off another elephant seal.

While they're swimming, special muscles close their nostrils and ears to prevent water from entering their respiratory system. Co-incidentally, these special muscles keep their nostrils automatically closed while they're sleeping on land.

Elephant seal youngsters, known as weaners, start swimming shortly after entering into their second month of life. They will start out by testing their skills in their local tide pools and stream deltas that empty into the ocean. As they get more proficient, they spend more and more time in the ocean searching for edible prey. ( See Unit on Weaners )

Diving

When at sea, adult elephant seals spend almost all of their time diving to the depths in search of their prey. Scientists have identified several different dive patterns which are associated with their travel, sleep and foraging.

Elephant seals are masters of conserving energy consumption, and this is particularly true when it comes to their dives.

Not only can they slow their metabolism rates by as much as 40-50% during their dives, but also reduce their heart rates from about 80-110 beats per minute on the surface to 30-35 beats per minute in the depths, thus lowering their energy consumption dramatically. ( An elephant seal's heart can even be slowed down to 2-3 beats per minute for a short period of time.)

To decrease oxygen consumption during a dive, scientists believe that the elephant seals are able to gradually close off the blood flow to their muscles, tissues, and internal organs, restricting the oxygen to their brain and central nervous system. ( Maybe this ability is similar to traveling on autopilot. )

Before starting out on one of its 2-3 times an hour foraging dives, the elephant seal exhales, emptying almost all of the air from its lungs. ( At the start of a dive, an elephant seal will have about 40% the amount of oxygen in its lungs that a human diver would, but it will have almost seven times the amount of oxygen stored in its blood and eight times as much in its muscles.)

Shortly after the start of the dive, the lungs of the elephant seal are collapsed causing any remaining air in its lungs to be expelled. ( This reduces the buoyancy and helps to protect the elephant seal from the bends. With no air in their lungs, there can be no exchange of gases between their lungs and their blood.)

When the animal's lungs are collapsed, oxygen is stored in its spleen, ready for use in any organ that needs it. The life-giving gas is attached to red blood cells and is then delivered around the body in liquid form.

Their fairly light bones also help in the neutral buoyancy so necessary to a successful diving ability.

In the first few minutes of the dive, the elephant seal swims rapidly downward making good use of its tail fins. Then, during the rest of the descent, about 90% of the dive, the elphant seal simply glides downward, maybe taking a cat-nap in the process.

For the ascent, however, the elephant seal has to make good use of intermittent tail-fin strokes to reach the surface. ( Elephant seals have a specialized lung surfactant that helps re-inflate their lungs without damage.)

Scientists also believe that the fine hair making up their fur helps to diminish their waterdrag. The necessity of fine hair may also be a reason for the need of the annual catastrophic molt as constant immersion in salt water will dry out the hair and make it coarser.

Spending only about two minutes at the surface between dives, the elephant seal takes 15-19 breaths a minute before diving down after food again.

Most of the time they dive down to the depths around 1600 to 1800 feet to a zone known as the ' deep scattering layer ' because of its affect on sound waves. This zone is extremely rich in marine life, containing hundreds of species of squid and fish, the favored prey of the elephant seal.

Feeding and Migration

According to scientists, all elephant seals make two long migrations each year in search of food starting from the beaches of Baja, Mexico and the California coast.

Scientists estimate that adult male elephant seals spend about 250 days at sea each year covering approximately 13,000 miles, while adult females spend about 300 days at sea traveling about 11,000 miles.

Of the adult elephant seals, the first such feeding migration of each year is taken by the adult females. They start to leave the birthing beaches in February and March after spending close to a month ashore giving birth, nursing their pups and then mating. Because these females have been ashore without food for close to a month, they need to replenish their supplies not just for themselves but also for the newly conceived life they're carrying inside them. This feeding trip lasts for about two months each year, and then the females return to the beaches they've just left so their catastrophic molt can take place and to get some rest.

Female elephant seals start out by heading north along the Pacific coast of North America, but then many branch out westward across the Pacific Ocean. Adult females mostly tend to stay between the latitudes of 40 and 45 degrees North. ( See chart below.)