So, what's a weanling?
Northern elephant seal moms leave their pups abruptly after about 4 weeks of nursing. During this time, most pups have tripled or quadrupled their mass, from a birth weight of 60-80 bs to about 300 lbs. Most northern elephant seal pups wean (stop nursing) between mid-January and mid-February, gathering with other weanlings in pods. Most weanlings spend 8-12 weeks on the beach during the post-weaning fast. Although it looks like fun and games by photogenic seals, this is a critical period of development of many of their body systems.
We burn our blubber while fasting!
Northern elephant seal pups gain 200+lbs in just 4 weeks of nursing with mom, and then fast (don't eat or drink) while they remain on the beach after weaning. During the 8-to 12-week post-weaning fast, weanlings stay alive by burning their blubber for energy.
Weanings lose weight while fasting on the beach.
Scientists have found that healthy weanlings lose from 1.25 lb. to as much as 1.9 lbs. per day during the post-weaning fast. Others have estimated a loss of one-half of one percent (0.5%) of their body weight each day, amounting to 25% of their post-weaning weight by the time they depart from the rookery. So, this means that a weanling that weights 300 lbs. at weaning, could weigh 225 lbs at departure for their first migration.
Hey, what’s happening with your hair?
Pups are born with a black coat (or pelage). The weanling sheds the black natal (birth) coat and it is replaced by smooth, short hairs that give a silverish appearance as the coat grows in. All weanlings complete the molt by the time they are 7 weeks old.
Take a look inside my mouth!
All northern elephant seal pups have deciduous (baby) teeth that they shed after birth and before weaning. Female weanlings precede males in the eruption of permanent canine teeth, often occurring before weaning. Males, on the other hand, may be delayed in the eruption of canine teeth, until as long as 4 weeks after weaning.
We like to swim when it's dark!
The time spent on the beach and in the water after mom leaves is a critical time in the development of weaned northern elephant seal pups. During the post-weaning fast, weanlings spend most of the time during day light hours sleeping. They are most active in the early morning and evening hours.
We can hold our breath for a long time!
Efficiently using oxygen is essential for elephant seals to successfully search for food (forage) underwater. They begin to develop these capabilities through lengthy periods of apnea (breath-holding) on the beach and while submerged in the near shore waters. Scientists have found that elephant seal weanlings quickly develop their ability to hold their breath, most for at least 6 minutes, some for as long as 10 to 12 minutes!
Not just sleeping- conserving energy!
There are so many things changing at once. Northern elephant seal weanlings lower their resting metabolic rate (the energy it takes to run their body systems at rest) by 40% by the time they have reached 7 weeks post-weaning. That helps to conserve blubber while fasting (not eating) too!
Our red blood cells are the envy of human athletes!
Like elephant seals, humans carry oxygen in hemoglobin within red blood cells. Both the concentration of hemoglobin and volume of red blood cells increase during the post-weaning fast. By the time elephant seals are only 3 months old, their blood has a higher oxygen -carrying capacity than adult humans!
Our amazing stunts and shunts!
Elephant seal weanlings love to do this acrobatic stunt, and develop their own signature moves!
So what about the amazing shunt? Breath holding helps weanlings to develop blood shunting- sending blood away from the surface tissues and towards vital organs and the brain. This will save oxygen and conserve heat while diving deep in the ocean.
Weanling elephant seals have a busy social life!
Weanlings cuddle, vocalize and interact with each other. They have altercations over space and mock fights. These interactions last from a few seconds to over a minute, and may include biting and nipping.
I'm just gonna keep swimming!
When elephant seals pups are born on the beach, they don't yet know that 80% of their lives will be spent underwater. Initially awkward, weanlings may explore shallow tidepools, float upside down, and remain underwater for just a few seconds. After 2-3 weeks of practice, their diving skills improve, allowing them to stay underwater for several minutes and even sleep underwater for 10-15 minutes.
Weanlings play with kelp while gaining mobility in the water. Destined to be champion divers and long-distance swimmers, it all starts with the first plunge.
We're leaving home for the first time!
There is a short window of time for northern elephant seal weanling departures for their first trip into the Pacific. Seals that are born at the beginning of the season (mid-December) may spend over 10 weeks on the beach after weaning and show the earliest departure from the rookery, in late March In contrast, those pups born later in the season are likely to spend less time (8 weeks) before departure in mid- April.
Optimal departure from the rookery is timed with the coastal upwelling, when more nutrients are available. Winds blowing across the surface push the warmer surface water away. The deeper water rises up from beneath the surface brings cold-nutrient rich water to the surface. More fish for these hungry weanlings!
Oh the places you’ll go! Following the weanlings to sea..
Where do weanlings go? Dr. Roxanne Beltran (UC Santa Cruz, Ecology & Evolutionary Biology Department) shared her research on the path of two weanlings on their first migration. Take a look!
How deep can they dive? Scientists have measured impressive improvements in breath-holding and deep diving skills over just their first few months at sea. As they improve, they become more efficient and use less oxygen, which enables them to dive deeper, for longer time periods. Learn more!
Why is this so important? Their food sources are deep underwater so deep-diving and long breath-holds are very important to be able to successfully forage (eat!) Plus, weanlings that can stay underwater for long periods and at deeper depths are able to stay away from the predators (sharks and orcas) that look for seals closer to the surface.
Want to learn more?
1. Take a virtual field trip with the Friends of the Elephant Seal and see the weanlings at the Piedras Blancas Northern Elephant Seal Rookery on our YouTube Channel.
2. Visit The Friends of the Elephant Seal website:
3. Share a weanling story with a book from our online store:
What's next?
The weanlings will return for the Fall Haul-out, beginning in early September. Join us in welcoming them back to the rookery!
Credits:
Photos by Phil Arnold, Max Fowles and Kathleen Curtis, Friends of the Elephant Seal