May 24, 2024

More than 1,000 sea lions have gathered at San Francisco’s Pier 39 this spring, the largest herd in at least 15 years.

Mounds of floppy, delightfully ungraceful marine mammals have plopped themselves on to rafts along the city’s pier, displaying themselves to the thousands of tourists who pass by the area each day.

According to the staff at the pier, the gathering has been attracted to a feast of anchovies in the bay. “With a steady food supply from a large school of anchovy, the sea lions are extra active!” the pier tweeted from its official account this week.

The charming pinnipeds have become a major attraction in the city since they first arrived at the pier about 35 years ago. The first – a big guy that staff had nicknamed Flea Collar because he had a piece of fishing net stuck around his neck – arrived in 1989. And then several hundred of his friends followed.

Sea lions bask at Pier 39. Photograph: Anadolu/Getty Images

Some years, as many as 1,700 sea lions at a time have stopped over at the pier. At other times, there have been just a few hundred. For those who are unable to visit in person, the pier provides a daily live stream of seal activity.

Many of the males at Pier 39 may be stopping there on their way south, to the Channel Islands off the coast of southern California, where they will meet up with females to mate, according to Dan Costa, a professor of ecology and evolutionary biology at UC Santa Cruz who specialises in marine mammals. “These are wandering, nomadic critters who tend to work their way north and work their way south throughout the year,” Costa said.

Sea lions meet up at Pier 39. Photograph: Anadolu/Getty Images

But researchers still don’t fully understand the movement and migration patterns of sea lions along the western coast. Costa’s lab has recently begun tracking female and juvenile sea lions along the California coast, both to better understand the animals’ migration patterns and to see how their movement and foraging might vary according to ocean conditions. Over time, researchers could also glean insights about how the climate crisis and warming ocean temperatures will affect the species.

In recent years, including during a marine heatwave off the US west coast that caused the formation of a warm “blob”, the fish that sea lions prey on became concentrated in pockets, rather than across a broader range, Costa said. That may be one of the reasons why there are more sea lions at spots like Pier 39 in some years than in others.

“But I bet a number of these guys are frequent visitors to Pier 39. Probably it’s one of their favourite places, and they keep coming back for the good food,” said Costa, not unlike visitors who stop by for a view of the bay and clam chowder in a bread bowl.

“And these sea lions are probably thinking, ‘Oh, look at all those tourists!’” he said.

Tourists observe hundreds of sea lions gathered on the docks at Pier 39. Photograph: Yuri Avila/AP

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