California Sea Lions – Pier 39, North Beach, San Francisco, California

The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of five species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic, males are larger than females, and have a thicker neck and protruding crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and white sharks.

California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females to mate with. Females are free to move in between territories, and are not coerced by males. Mothers nurse their pups in between foraging trips. Sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside of their breeding season, sea lions spend much of their time at sea, but they come to shore to molt. Sea lions are particularly intelligent and can be trained to perform various tasks. Because of this, California sea lions are commonly found in public displays in zoos, circuses and oceanariums, where they are known as the classic "seals," and are trained by the US Navy for certain military operations.

California Sea Lions have always been present in San Francisco Bay. They started to haul out on docks of Pier 39 in September 1989. Before that they mostly used Seal Rock for that purpose. Ever since September 1989 the number of sea lions on Seal Rock has been steadily decreasing, while their number on Pier 39 has generally increased. Some people speculate that sea lions moved to docks because of the 1989 Loma Prieta earthquake, but the earthquake occurred months after the first sea lions had arrived at Pier 39. It is likely that the sea lions feel safer inside the Bay.

Although the reason for their migration to the pier is unclear, the refurbishing of the docks in September 1989 required the removal of all boats from that area, leaving large open spaces for the sea lions to move into. Once the project was completed, boat owners returned, but did their best to navigate around the sea lions; no efforts were made to encourage the new guests to leave. By the end of that year, less than a dozen sea lions frequented the docks at Pier 39. By January 1990, their numbers had increased to 150 animals. Owners of the 11 boats docked there began to complain about having to avoid the animals who can weigh up to half a ton, and odor and noise complaints began to pour in. Press releases caught national attention, and the sea lions began to attract tourists. Advice from The Marine Mammal Center was to abandon the docks to the animals, and to relocate the boats elsewhere.

There are dramatic fluctuations in the number of sea lions at Pier 39 are dramatic, with as many as 1,701 having been officially reported at one time. Many of whom are recognizable to researchers and some of them have been unofficially named. Scientists continue to collect information there, adding to knowledge about sea lion health, dietary habits, and behaviour. In November 2009 the sea lions that had lived at the pier began to leave, and by late December 2009 nearly all were gone. A similar flux in population occurs annually, with the animals returning in the spring. Although the reason for their seasonal appearance and departure is not known for certain, according to Jeff Boehm, executive director of the Marine Mammal Center in Sausalito, "Most likely, they left chasing a food source," anchovies and sardines. A handful of sea lions did return in February, and by late May several hundred could once again be seen. It remains unknown exactly where they went and why. However, in December 2009, nearly 4,000 sea lions that were identified as members of the California sub-species were seen outside Oregon’s Sea Lion Caves, which meant that they were likely the sea lions from Pier 39.

Similarly, in late June 2014, the sea lions suddenly disappeared, leaving in their wake not only wood docks stained with white scat and hordes of disappointed sightseers, but also questions about the uncertain ways of the wild. On one hand, it's not unusual for the sea lions around Fisherman's Wharf to leave their docks, particularly at this time of year, said marine scientists. The early summer months are when the animals migrate, mostly south to the Channel Islands off the Southern California coast to rear their young. But for so many to go at once – even the sea lions that are too young to breed – is odd, said Monica DeAngelis, a marine mammal biologist with the National Oceanic and Atmospheric Administration. Just as unexpectedly, they returned in the first week of August.