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
1989 Loma Prieta earthquake
1989 Loma Prieta earthquake
Pier 39