Harbor Seals: At Home in the Bay

Aug 1, 2013

Deb Self, Baykeeper Executive Director 

Have you walked along the shores of San Francisco Bay and spotted a dark head in the water, with big eyes looking back at you? From the safety of water, a harbor seal will often curiously watch people walking on the beach. Harbor seals can also playfully bump swimmers, although they have been known to bite.

Once "hauled out" and resting on a beach or a mudflat, harbor seals are skittish. With their short flippers, they can only flop along on their bellies. At the sight or sound of humans or boats that approach too close, hauled-out harbor seals immediately lunge into the water.

Harbor seals (Phoca vitulina richardii) are smaller than the sea lions who charm visitors at Pier 39. Another quick way to tell the difference: sea lions have visible ear flaps and harbor seals have none. Unlike sea lions, harbor seals live year-round in and alongside San Francisco Bay. They spend about half their time in water, where they are swift and graceful, propelled forward by their powerful hind flippers.

"If you approach a harbor seal and change its behavior, you’re too close," said Doreen Gurrola, a marine science educator at the Marine Mammal Center in Sausalito. The federal Marine Mammal Protection Act requires people and boats to stay at least 300 feet away. However, Gurrola said, "If a seal pops up in the water and you’re on the beach or in a boat, you shouldn’t move closer, but you don’t have to move 300 feet away."

Staying 300 feet away is especially important near harbor seals’ longtime haul-out sites around the Bay, which include beaches, mudflats and rocky outcroppings exposed only at low tide, and wetlands covered with vegetation. Although development along the Bay’s edges has destroyed many former sites, harbor seals still haul out along San Francisco Bay’s shores. If left undisturbed, generation after generation will use the same haul-out site.

Harbor seals eat a variety of seafood, including sole, flounder, sculpin, herring, octopus and squid. They weigh up to 300 pounds and can live as long as 30 years. Females give birth to a single pup between March and May. At birth, pups weigh about 20 to 24 pounds and can swim immediately. Pups sometimes ride on their mothers’ backs. They make a bleating "maaaa" sound. Mother seals nurse their pups on land only, and pups gain almost a pound a day. After about a month, the pup is weaned and must catch fish on its own. This year’s pups now weigh 50-60 pounds, and will take five years to reach adulthood.

In order to nurse, mother seals need to feed in the water. They sometimes leave pups for short times alone on beaches. If you see a seal pup on a beach, it is probably not stranded or orphaned; the mother will most likely return soon to nurse the pup. Remember never to approach a pup, because the presence of humans can keep the mother away and lead to the death of the pup.

Harbor seals have spotted coats in various shades of white, silver-gray, dark brown, and black. Many of San Francisco Bay’s harbor seals have reddish coats, possibly because the water contains trace elements like iron or selenium. Harbor seals are at the top of the Bay’s food chain, and their bodies have a high fat content. This makes pollution from some toxic industrial chemicals and pesticides especially harmful, because these substances can build up in their bodies at levels that threaten their health and lives. San Francisco Baykeeper is working to stop pollution in the Bay, so that harbor seals and all Bay wildlife can thrive.

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