Why Are There Sea Lions at Pier 39? San Francisco's Colony

How the sea lions arrived at Pier 39

Before 1989, sea lions in the San Francisco area hauled out mainly on Seal Rocks, off the Cliff House on the city’s Pacific shore. In late 1989, a few California sea lions began resting on K-Dock, a set of floating boat docks in Pier 39’s West Marina on the bay side of the city.

Pier 39 dates the first arrivals to shortly after the Loma Prieta earthquake of October 17, 1989, and the earthquake is often said to have driven the animals there. Other accounts say the first few sea lions arrived a few weeks before the quake, while the docks were being rebuilt and the boats had been moved out. No one knows for sure, and there is no evidence that the earthquake itself was the cause.

What is clear is what happened next. By January 1990 about 150 sea lions were crowding the docks, and within a few months there were more than 300. Boat owners complained about the noise, the smell and animals weighing several hundred kilograms climbing onto their slips. The marina asked The Marine Mammal Center, a rescue and research organization in nearby Sausalito, for advice. The experts recommended letting the sea lions stay, the boats were moved elsewhere, and K-Dock became the sea lions’ home.

Why do sea lions like Pier 39?

Three things make the docks attractive:

• Food nearby. San Francisco Bay and the waters outside the Golden Gate are rich in fish. Pacific herring come into the bay to spawn in winter, and large schools of anchovies and sardines move in at times. Sea lions can feed and then haul out a short swim away.
• Safety. Inside the bay, sea lions are far from most of their natural predators, orcas and great white sharks, which hunt mainly along the outer coast and around the Farallon Islands.
• Easy, stable resting space. Floating docks sit just above the water, rise and fall with the tide and are easy to climb onto from the water. Unlike rocks and beaches, they are never covered at high tide.

Just as important, nobody chases the sea lions away. California sea lions are protected by the US Marine Mammal Protection Act, and Pier 39 chose to keep the docks for them rather than for boats.

Are the sea lions at Pier 39 all year?

The colony is a haul-out, a resting place, not a breeding colony. California sea lions breed mainly on islands off Southern California, such as the Channel Islands, and in Mexico. Most of the animals at Pier 39 are males, adults and younger animals, that spend the non-breeding season feeding along the central and northern coast.

As a result, numbers rise and fall with the seasons and with the food supply. Many sea lions leave in early summer, especially in June and July, to head south for the breeding season, and numbers can drop very low. They build up again from late summer through autumn, winter and spring. In recent years, Pier 39 staff have reported typical counts of around 300–400 in winter and up to about 700 in spring.

The 2009 disappearance

The most famous change came in 2009. In autumn that year, about 1,700 sea lions crowded onto the docks, the highest count recorded until then. Then, in late November and December, almost all of them left. By late December the docks were nearly empty, and the mystery was widely reported.

Experts thought the sea lions had followed their food. Around the same time, unusually large numbers of California sea lions were reported off the Oregon coast, far to the north, and many believed the Pier 39 animals were among them. A handful came back in February 2010, and by late May several hundred were again resting on K-Dock. The episode showed how closely sea lion numbers track the movements of fish such as anchovies and sardines.

Record crowds in 2024

In spring 2024, big schools of anchovies and herring in San Francisco Bay drew sea lions in numbers not seen for about 15 years. More than 1,000 were counted on the docks in late April and early May, and Pier 39 reports that numbers then rose to an all-time record of more than 2,100 in May and June 2024. Marine mammal experts noted that such surges mostly reflect where the fish are, not a sudden jump in the total sea lion population.

What the Pier 39 colony shows about sea lion behavior

Pier 39 gives visitors a close look at everyday sea lion life. The animals pile together to rest, often sleeping in tangled heaps in the sun. They shuffle for space, push rivals off the docks and bark constantly while doing so, which is why the colony is so noisy. The reasons behind all that barking are explained in Why do sea lions bark?

Visitors can also see how sea lions control their body temperature, fanning flippers in the air or sliding into the water to cool off. Some individuals are recognizable to researchers from scars or other markings. Naturalists at a sea lion education center on the pier, run by the Aquarium of the Bay, explain this behavior to visitors, and staff and volunteers keep track of numbers and watch for animals that are sick or entangled.

Visiting the sea lions

The sea lions can be watched for free from the west side of Pier 39, near Fisherman’s Wharf, where K-Dock is overlooked by railings and viewing areas. A live webcam also shows the docks.

The sea lions are wild animals. Feeding, touching or harassing them is illegal, and large males can bite if people get too close. The safety rules are explained in Are sea lions dangerous?