More than 70 native fish species can be found in the San Francisco Bay. Many of these species are transients, short term visitors from nearby ocean or freshwater habitats. Some are migrants, such as Chinook salmon and sturgeon, crossing the Bay between the ocean and their spawning grounds in rivers. 33 species of native fish are completely dependent on the Bay, living and raising their young here.
In addition to the native fish species, a number of other fish species have either invaded the Bay, or have been introduced. Striped bass, for example, were introduced in 1879 for fishing. Although the number of introduced and invaded fish species has increased, the Bay fish community is still dominated by native species.
Eleven species of shark call the San Francisco Bay home, with at least five species living in the Bay year-round. The six foot long Leopard Shark is the most common and the most colorful of the shark species found here. Harmless to humans, it feeds on crabs, shrimp and herring.
In addition to the occasional lost minke or gray whale, four species of marine mammals are often seen in the Bay. Large numbers of California sea lions haul out at Pier 39, presumably because it’s a safe place away from predators. Sea lions do not breed in the Bay, but show up after breeding has finished in the Channel Islands in southern California in August, with some sea lions present all year. These highly social mammals are very vocal and can almost always be found somewhere in the Bay.
Pacific Harbor Seals haul out at Yerba Buena Island, and actively forage in the Bay all year. Harbor porpoises have recently returned to the Bay. Historically present in small numbers, they vanished from the Bay by the 1940s, due to ship traffic and environmental degradation. The final straw for these sensitive mammals was probably the steel net the navy installed between Sausalito and San Francisco during World War II to protect the harbor from submarine attack. Harbor porpoises are among the most elusive of the marine mammals and usually a quick view of a dorsal fin is all a human observer will see.
Bottlenose dolphins are now found regularly. Prior to the 1982-83 El Nino that brought warm water to northern California, these playful animals were rarely seen north of southern California. The expansion of warm water allowed them to range further north, and when the water cooled, the dolphins stayed, expanding their range.
More than a million birds stop or stay on the San Francisco Bay. It’s a critical stopover and wintering spot on the Pacific Flyway for many species of shorebirds and waterfowl. More than 300,000 shorebirds show up every year and the number of ducks can be in the hundreds of thousands every winter.