Inverness, California 3/4/04
Being on a beach with a colony of elephant seals is in many ways like watching a large family interact. The largest male (or alpha male) does not do anything unless his position is truly threatened, the mature females look after their babies and make themselves comfortable, the young males try and get a little action going while the young females observe the scene.
Richard and I were on the Great Beach one afternoon in January accompanying the senior scientist for Point Reyes National Seashore, Dr. Sarah Allen, as she pursued her research into these amazing animals. Our adventure began when we walked down a canyon just north of the Point Reyes Lighthouse. The lupine was sprouting new growth. We finally reached the beach and spotted several adult males lying nearby on the sand. We observed them quietly for a few minutes then Sarah slowly walked towards a solitary male. When she was a few feet away from him, she gently threw a little sand on his tail. He did not respond, so she efficiently tagged him with a special marker staple. He immediately reacted by drawing himself up and facing Sarah who withdrew a safe distance. The elephant seal then settled down once more.
Most of the male elephant seals had already been tagged. The colors of their tags indicate where they had been tagged. Sarah carefully walked up to them and read their tags. Some were local (pink tags), others had travelled up from Ano Nuevo or Piedras Blancas in the south. Further down the beach we reached the heart of the colony - twelve females, ten pups, the alpha male and a few young males. Many pups were nursing. They weigh 60 - 80 pounds at birth and increase their weight by about ten percent every day until they weigh a whopping 300 pounds when they are weaned at a month old. Elephant seal milk is very rich (50 percent fat). To translate that figure into human terms: half and half milk is actually only 10 percent fat. While they are feeding their young, the females have absolutely no interest in mating. In fact while we watched, a young male tried to mount a female. She swung around and slapped him hard where it hurt with her flipper! The alpha male, perhaps realizing there was no threat to his position as head of the harem, did not interfere.
The females come into estrus about a month after giving birth. They leave the colony within days of mating to eat. However the embryo does not implant for another six weeks. It divides into 64 cells. This is called the blastula stage when the embryo floats freely within the uterus. After the female has been at sea about six weeks it secretes a hormone which causes it to molt and she returns to shore. The blastula then implants and starts growing. As the gestation period is about nine and a half months, this ensures that the female will be on a yearly cycle and that all the females will give birth within a few weeks of each other.
After their mothers leave, the pups, now known as “weaners” will stay on the beach for another four weeks. During this time they will lose about a third of their weight. Some become “super weaners” by nursing off other females after their own mothers have left the beach. Finally they all teach themselves to swim and take off on their first foraging trip.
Elephant seals spend most of their lives in the ocean and ninety percent of that time is underwater. They dive to tremendous depths to feed. The average dive reaches 1,000 to 2,000 feet, lasts close to half an hour and is followed by only 3-5 minutes at the surface to breathe. They feed in almost total darkness. Their large eyes help them see in the dark by gathering any available light. Some of their prey, like octopus and squid, is bioluminescent which means they glow in the dark. They also feed on Pacific hake, skates, rays, shrimp, small sharks and crabs that they may “feel” with their stiff yet sensitive whiskers which are from 3 to 8 inches long. At the depths that they forage, they face little competition for food.
What allows such deep diving? Pressure increases as you go deeper into the ocean. As you dive, the pressure on the outside compresses the air in your body. When elephant seals dive, they carry all the oxygen they need in their blood rather than in their lungs. Before they dive, they exhale, collapsing their lungs so there is little air to be compressed. As they dive, their fat is also compressed so that they lose their buoyancy and sink, allowing them to achieve great depth with little effort.
Elephant seals prolong their dives by reducing their heart rate. A seal resting on land has a heart rate of 55-120 beats per minute, but when it dives, its heart slows to 4 -15 beats a minute. The seal maintains normal blood pressure by decreasing the blood supply to its extremities, allowing the blood to flow primarily to the vital organs and the brain. This also helps the seal conserve body heat when down in the cold ocean depths. Through monitors placed on elephant seals, scientists have determined that elephant seals sometimes sleep when diving. The longest recorded dive is 119 minutes while the deepest recorded dive is over 5,000 feet.
The males are much larger than the females. They weigh between three to five thousand feet and grow as long as 19 feet while females weigh between 900 and 1800 pounds and measure between nine to twelve feet. The females live up to twenty years while the male lifespan is generally only fourteen years. In the 1800’s elephant seals were hunted extensively for their blubber. A male could yield 25 gallons of lamp oil. By 1910 there were estimated to be less than a hundred on Guadalupe Island in Mexico. Now the population is over 150,000 probably near their number before they were over-hunted. Southern elephant seals which are found throughout the sub-Antarctic regions, are a larger than their Northern cousins. The males grow to 21 feet and weigh 7,780 pounds while the females weigh 1980 pounds and measure up to 11.5 feet. Their territories never overlap with the Northern elephant seals.
Excursion #2
In early March Richard and I once again photographed an elephant seal colony. This one was at the northern end of Drakes Bay. These pups were older and therefore much larger than those we had seen on the Great Beach. In fact some seemed to be so chubby they could barely move! There were about 65 pups, several large males and two females. The pups were beginning to spread out along the beach, an indication that they were getting ready to forage in the ocean. We were escorted to the colony by Jerry Nusbaum, Sarah’s assistant, who has spent 26 winters on the Farallon Islands carrying out seal research. Here, he was tagging as many of the pups that he could. He said that on the Farallones over several years he had tagged three generations of seals who chose to give birth within five feet of their own birth place. “I suspect they are doing the same here too,” Jerry said.
It is amazing how often when one goes out to observe animals one gets caught up in a dramatic scene in which the animals seem to be experiencing great emotional turmoil. We noticed a female making her way down to the waves and wondered if she was planning to leave the colony. Her pup followed her to the water’s edge. A male was swimming nearby and started moving towards her. She looked at him and headed his way. Suddenly a large elephant seal on the beach noticed the potential assignation. He gathered up his body and moved his huge torso with amazing speed. Within seconds he was by the side of the female and had his flipper on her body holding her against his own body, tucking himself around her. They lay in the shallow waves like this for a while. With the pup hovering nearby it actually looked like a loving tableau. Then the male mounted her while the pup yelped and splashed around them. The actual mating took about a minute and then the male moved away and rested on the shore. The female remained in the water with her pup. It was very likely the first time the pup had ever been in the ocean. Instinctively seal pups will do a dog-paddle, as they are descended from four-legged creatures – and this is what this seal pup did. He also flapped his tail to try and keep afloat and squealed almost continuously. The alpha male moved back up the beach towards the cliffs. As soon as he was settled, the male in the water started to swim towards the female. When they were about five yards apart, the alpha male once again realized what was about to happen and came charging down the beach. The second male again avoided conflict by swimming away. At this point we had to leave so I never discovered the final outcome. I suspect that the alpha male continued to rule the roost, the female went off to sea and the weaner learned to swim!