Cambrian: Opinion

Taking attendance among elephant seals at Piedras Blancas rookery

Male elephant seals stay cool in piles of kelp at the water’s edge.
Male elephant seals stay cool in piles of kelp at the water’s edge.

Small seals are joining the big, mature bulls on the beach at Piedras Blancas in August. It’s time for the adults to move back into the ocean and youngsters to surf in.

The fall months of September, October and November are the Juvenile Haul-Out. The smallest seals are the Young of the Year, the pups that were born during the previous breeding season. Only about half survive the first migration, the others eaten by predators or unable to catch enough food to survive. They may be no larger than when they left as weaners, but they have survived. Any seal that arrives on the beach for the haul-out is a survivor.

Even on their first migration, pups are able to dive as deep as 4,000 feet. We don’t know how they find their way north to hunt fish and squid along Canada’s west coast. Some get as far north as the Aleutians, where the adult males feed.

During the month of transition from adult males molting to juvenile haul-out, the big mature bulls pile up among younger males. Young males and females are difficult to tell apart. Females never grow a long nose, a proboscis, but males start growing that nose, and the crinkled skin of their chest shields, when they reach 5 years old. Many are big, but the size of the nose is an indicator of how old they are.

Younger seals are typically less dominant that older seals, even if they are big. But they spar a lot with each other. Dominance will be important to them in the future. Only the most dominant males get to breed.

Bulls are considered mature when they are 8 years old, but the nose and chest shield keep growing through their lives. Last week, there were several bulls with noses so long, they must be quite senior.

Their blubber insulates them from the wide variations of temperature they confront, from the cold conditions of Northern Pacific waters to warm, sunny California beaches. Conserving energy is important, because they aren’t eating anything while they are here on the beach. They are living off their blubber.

Humans need to keep body temperature within narrow limits, but elephant seals’ core temperature can range 12 degrees around their normal 99 degrees. Seals in one group that researchers measured varied 18 degrees, from 87 to 105.

On land, that allows them to heat up during the day and cool down at night. Piling up and lying on top of each other at night exposes less of each seal’s skin to the cool air, keeping them warm. As the sun warms them up, they move away from each other. Most make their way to the cool sand and lapping waves at the water’s edge.

Flipping sand onto themselves helps, too. Sand keeps the skin cool.

Another adaptation is a secondary blood circulation system that helps them regulate their temperature. Blood, warm from the internal body core in the arteries, can be shunted past the capillary system to flow freely near the skin to cool off.

The bulls are leaving to feed along the continental shelf along the Canada and Alaska coast. They’ll return in December for the breeding season.

Christine Heinrichs’ column appears the fourth Thursday of each month and is special to The Cambrian.