Cambrian: Opinion

Juvenile elephant seals returning to Piedras Blancas

A shark bite is clearly visible on a juvenile elephant seal at Piedras Blancas.
A shark bite is clearly visible on a juvenile elephant seal at Piedras Blancas.

October is a busy month at Piedras Blancas, with hundreds of juvenile seals arriving for fall haul-out. That means they haul themselves out of the surf onto the beach. Most of these seals are less than 5 years old, the age when the males start growing that distinctive nose.

The smallest seals are the young of the year, the pups born in January. Those on the beach have survived their first migration. Only half of the pups make it. They may not have gained much weight, but any seal on the beach is a survivor.

These fat, young seals make a good meal for great white sharks, which migrate to the Central and Northern California coast in the fall. Young seals are more desirable prey than mature bulls, which are formidable opponents and can fight back.

Great white sharks typically attack from below and behind their prey. The relationship between predator and prey is a balance, between attack and avoidance. UC Santa Cruz researcher Sarah Kienle is studying elephant seal feeding behavior at Guadalupe Island off Baja California. Her collaborators have observed that seals returning to that island are likely to approach the beaches from below.

“Seals hug the bottom, making it difficult for sharks to attack,” she said.

In response, it seems that white sharks are changing their behavior, and attacking seals from above. Seals there had shark bite wounds on their backs, rather than their bellies. She watched sharks patrol the beaches, back and forth and up and down.

“Every animal we saw had some kind of wound,” she said.

Sharks swim along the Central Coast, but the area hasn’t become a feeding ground. Sharks head for the Farallon Islands, Tomales Bay, Año Nuevo and other points north to feed on the young elephant seals migrating back to Central Coast beaches. An elephant seal meal gives sharks the rich blubber they need to store energy in their livers for their own migration across the Pacific in the winter.

They swim as far as 2,000 miles to the White Shark Café, halfway from California to Hawaii. It was identified when tagging sharks made it possible to follow them electronically. It’s in an area otherwise thought to be an ocean desert, with few resources. The sharks may be feeding there, or they may go there to breed.

White sharks are legally protected in the U.S. It’s against the law to catch them, either commercially or recreationally. White sharks are ocean rovers, and other countries do not protect them, so they are being fished in other places for their meat and their fins. The International Union for Conservation of Species classifies the species as vulnerable.

Elephant seals are also protected, by the Marine Mammal Protection Act, but their population is doing well. They are not endangered or threatened.

“They are a sentinel species, so it’s good to know what they are doing,” Kienle said.

It’s a ballet between predators and prey. No seal is willing to be eaten, but they are all part of the web of nature.

Get involved

Be an Elephant Seal Ambassador for State Parks. Greet visitors, tell them about the elephant seals and direct them from Hearst Memorial Beach and Arroyo Laguna to the viewing area at Piedras Blancas. Ambassadors are needed during the breeding season, January through March. Training will be held Saturday, Dec.16. The deadline to apply is Nov.r 30. For a volunteer application, email SLOCoast.Hearst@gmail.com or call Robyn Chase at 805-286-0856.

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