Cambrian: Opinion

Weaners conserve energy, prepare for journey north to Alaska

Satisfied weaners snooze the day away. The one in the center is still molting his baby black coat.
Satisfied weaners snooze the day away. The one in the center is still molting his baby black coat. Special to The Cambrian

The beach at Piedras Blancas is quiet in March and April. Mostly weaners sleeping. Between naps, they go into the water, to practice holding their breath and learn to swim. As the days pass, they spend more time in the water, swimming and diving, until they are ready to launch into their first migration.

Perhaps it’s an evolutionary disconnect, but they are unable to swim when they are born, despite the fact that they will ultimately spend most of their lives deep under water. When they are born, they are in danger of actually drowning if they are washed out to sea on a high tide. As they mature, they will spend eight to 10 months a year diving continually to 1,000 feet and deeper.

By March, they have been weaned from nursing and gaining weight — hence the term “weaners.” As they sleep on the beach and cavort in the surf, their metabolism is changing. They don’t have anything to eat on the beach. They spend the next eight to 10 weeks without food, living off that blubber. Their bodies convert some of it into muscle. They also increase the amount of blood and the oxygen-carrying capacity of their muscles, important adaptations to allow them to dive deep. The black coats they were born with are replaced with lighter tan and silver coats. 

At some point, each of the weaners feels the unknown call of the sea, and enters the water to begin its first migration. They may not get all the way to Alaska this first year, but they somehow know where to go. A few wash up on local beaches and are rescued. They will get supportive feeding until they are able to take on the ocean for themselves, then be set free. 

About half never return, part of the cycle of life. Those that aren’t able to catch enough prey starve, and others become prey themselves. The circle of life.

Those that succeed will find their way back to island and mainland beaches along the West Coast in September. About three-quarters return to the beach where they were born.

A few adult bulls remain on the beach, sleeping and resting from the rigors of the three-month breeding season. Soon they will join all those that have already left, migrating up to Alaska to gorge on fish and squid, and gain weight for the coming year. There are always a few stragglers. Biological systems are usually distributed as a bell-shaped curve, with some early, some late and most in the middle.

Watch for whales

Look beyond those sleepy weaners for whale spouts in the open ocean. Gray whales are migrating from their breeding and calving grounds in Baja California north to their feeding grounds in the Arctic from March through May. 

Mothers and their calves swim close to shore during the northward migration to avoid orca attacks. 

By staying close to the surf line, they take advantage of the pounding surf to camouflage them. 

The shallow water also helps protect them, since orcas attack from below. If orcas are around, gray whales will come right up into the rocks and stay still to avoid detection.

Whale scientist Wayne Perryman monitors the whale count from the Piedras Blancas Light Station. 

In 2014, he and his team counted 431 calves, the fourth-highest total in the 21 years that he’s been doing it.