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.
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.
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!
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.
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.