Aquatic mammals are also present in the bay . Before 1825 , Spanish , French , English , Russians and Americans were drawn to the Bay Area to harvest prodigious quantities of beaver , river otter , marten , fisher , mink , fox , weasel , harbor and fur seals and sea otter . This early fur trade , known as the California Fur Rush , was more than any other single factor , responsible for opening up the West and the San Francisco Bay Area , in particular , to world trade . By 1817 sea otter in the area were practically eliminated . Since then , the California golden beaver has re-established a presence in the Alhambra Creek . The North American river otter which was first reported in Redwood Creek at Muir Beach in 1996 , has since been spotted in the North Bay 's Corte Madera Creek , the South Bay 's Coyote Creek , as well as in 2010 in San Francisco Bay itself at the Richmond Marina . Other mammals include the internationally famous sea lions who began inhabiting San Francisco 's Pier 39 after the 1989 Loma Prieta earthquake and the locally famous Humphrey the Whale , a humpback whale who entered San Francisco Bay twice on errant migrations in the late 1980s and early 1990s . Bottlenose dolphins and harbor porpoises have recently returned to the bay , having been absent for many decades . Historically , this was the northern extent of their warm-water species range
1989 Loma Prieta earthquake
1989 Loma Prieta earthquake
San Francisco Bay Area