Weaners balance blubber and muscle
Weaners prepare to face their lives in the open ocean in March. They venture into the surf to practice diving, swimming and holding their breath. Watch a video on the Friends of the Elephant Seals YouTube channel.
The atmosphere on the beach is peaceful, following the
drama of breeding season. A few bulls remain on the beach, resting up,
unconcerned with the weaners.
The bulls are at their thinnest, having lived on their
blubber for more than three months. The recently weaned pups are at their
fattest.
Blubber into muscle
Feeding ended when their mothers left. Until they
begin catching fish on their first migration, they rely completely on their
blubber.
They take this time on the beach to exercise, improve
their swimming skills in the surf and turn some of that blubber into muscle. They
are more likely to be in the water at night, but you may see them splashing
around during the day. Their life deep in the ocean will require them to hunt
in the dark depths.
Balancing blubber and rest
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Generally, bigger is better for elephant seals, but
there’s a balance. Size, weight and blubber figure in dominance, staying warm,
and having physical resources to survive. Pups need enough blubber to draw on
after they stop nursing to launch them into success in the ocean. They need to
dive and catch prey to feed themselves.
Blubber is buoyant, though. Fatter weaners struggle to
dive to depth where they can hunt and feed.
Two scientists at UC Santa Cruz have followed adult
females, “to better understand the
behavior of a wild animal trying to find food while trying to avoid becoming
food.” Roxanne Beltran and Jesse Kendal-Bar evaluated data from tracking
devices. They found the females balance the need for food against the danger of
sleeping, depending on how light it is.
During the light of day. the seals are at risk of
being attacked by sharks. They are safer resting deep in the dark ocean depths
during the day. Thin seals who need to put on blubber are more inclined to risk
resting during the day, when it’s lighter, and spending more time feeding at
night, when they don’t have to dive as deep to forage.
As they put on blubber, they are more inclined to rest
at night, when they are safer. They are safer awake than asleep, but they have
to sleep sometime.
The researchers call it the Lightscapes of Fear. They
intend to use this insight to inform research on other, land-based, species.
Weaners are in danger
during their first migration. Only half of them survive to return to the beach
in September.
Stranded weaners