San Francisco Bay Area - Ecology

Ecology

Despite its urban and industrial character, San Francisco Bay and the Sacramento-San Joaquin Delta remain perhaps California's most important ecological habitats. California's Dungeness crab, Pacific halibut, and Pacific salmon fisheries rely on the bay as a nursery. The few remaining salt marshes now represent most of California's remaining salt marsh, supporting a number of endangered species and providing key ecosystem services such as filtering pollutants and sediments from the rivers. Most famously, the bay is a key link in the Pacific Flyway. Millions of waterfowl annually use the bay shallows as a refuge. Two endangered species of birds are found here: the California least tern and the California clapper rail. Exposed bay muds provide important feeding areas for shorebirds, but underlying layers of bay mud pose geological hazards for structures near many parts of the bay perimeter. San Francisco Bay provided the nation's first wildlife refuge, Oakland's artificial Lake Merritt (constructed in the 1860s) and America's first urban National Wildlife Refuge, the Don Edwards San Francisco Bay National Wildlife Refuge (SFBNWR) (1972). The Bay is also invaded by non-native species.

Steelhead trout (Oncorhynchus mykiss) populations in California have dramatically declined due to human and natural causes. The Central California Coast distinct population segment (DPS) was listed as threatened under the Federal Endangered Species Act on August 18, 1997; threatened status was reaffirmed on January 5, 2006. This DPS includes all naturally spawned anadromous steelhead populations below natural and manmade impassable barriers in California streams from the Russian River to Aptos Creek, and the drainages of San Francisco, San Pablo, and Suisun Bays. The U.S. National Marine Fisheries Service has a detailed description of threats.

The Central California Coast Coho salmon (Oncorhynchus kisutch) Evolutionary Significant Unit (ESU) population is the most endangered of the many troubled salmon populations on the West Coast. It was listed as threatened on October 31, 1996 and later downgraded to endangered status on June 28, 2005. The ESU includes all naturally spawned populations of coho salmon from Punta Gorda in northern California south to and including the San Lorenzo River in central California, as well as populations in tributaries to San Francisco Bay. The National Park Service has made major recent investments in restoring the tidal wetlands at the mouths of Lagunitas Creek and Redwood Creek including levee removal and placement of large woody debris in the creeks, which provide shelter to salmonids during heavy stream flows and flooding. Lagunitas Creek's coho population is especially important, as 80% of the ESU depends on this stream draining the north slope of Mount Tamalpais. This year's coho count dropped to 64 from an average of 600 in previous years.

Western Burrowing Owls (Athene cunicularia) were listed as a Species of Special Concern (a pre-listing category under the Endangered Species Act) by the California Department of Fish and Game in 1979. California's population declined 60% from the 1980s to the early '90s, and continues to decline at roughly 8% per year. In 1994, the U.S. Fish and Wildlife Service nominated the Western Burrowing Owl as a Federal Category 2 candidate for listing as endangered or threatened, but loss of habitat continues due to development of the flat, grassy lands used by the owl. A 1992–93 survey reported no breeding burrowing owls in Napa, Marin, and San Francisco counties, and only a few in San Mateo and Sonoma. The Santa Clara County population is declining and restricted to a few breeding locations, leaving only Alameda, Contra Costa, and Solano counties as the remnant breeding range. Despite organized protests at Kiper Homes' Blue Ridge property in Antioch, California by Friends of East Bay Owls, one-way doors were installed in the birds' burrows so that the owl families could not return to their nests in early 2010. In addition, in 2008, Mountain View, California evicted a pair of burrowing owls so that it could sell a parcel of land to Google to build a hotel at Shoreline Boulevard and Charleston Road. Eviction of the owls is controversial because the birds regularly reuse burrows for years, and there is no requirement that suitable new habitat be found for the owls.

Much of the SFBNWR consists of salt evaporation ponds acquired from the Leslie Salt Company and its successor, Cargill Corporation through a series of land sales and donations. Many of these salt ponds remain in operation and produce salt used throughout the Western United States in food, agriculture, industry and medicine. The refuge pond support dense populations of brine shrimp, and therefore serving as feeding areas for waterfowl. In 2003, the US Fish & Wildlife Service and California Department of Fish & Game entered one of the largest private land purchases in American history, with the state and federal governments paying $100 million for 15,100 acres (65 km²) of salt ponds (which government appraisers valued at $243 million prior to the acquisition) in the south bay and 1,400 acres near the Napa River. SFBNWR and state biologists hope to restore some of the recently purchased ponds as tidal wetlands.

Aquatic mammals recently re-colonizing the Bay Area include the California Golden Beaver (Castor canadensis) which is now established on Alhambra Creek in Martinez, Napa River and Sonoma Creek; and North American River Otter (Lontra canadensis) which was first reported in Redwood Creek at Muir Beach in 1996, and recently in Corte Madera Creek, and in the south Bay on Coyote Creek, as well as in 2010 in San Francisco Bay itself at the Richmond Marina. Sea otter (Enhydra lutris) were hunted to extinction in San Francisco Bay by about 1817. Historical records reveal that the Russian-American Company snuck Aleuts into San Francisco Bay multiple times, despite the Spanish capturing or shooting them while hunting sea otters in the estuaries of San Jose, San Mateo, San Bruno and around Angel Island. The founder of Fort Ross, Ivan Kuskov, finding otter scarce on his second voyage to Bodega Bay in 1812, sent Russian ships and hired an American ship to hunt otter in the Bay, catching 1,160 sea otter in three months.

Humphrey the Whale, a humpback whale (Megaptera novaeangliae), entered San Francisco Bay twice on errant migrations, and was successfully rescued and redirected each time in the late 1980s and early 1990s. This occurred again with Dawn and Delta a mother and calf in 2007.

The seasonal range of water temperature in the Bay is from about 8 °C (46 °F) to about 23 °C (73 °F).

Industrial, mining, and other uses of mercury have resulted in a widespread distribution of that poisonous metal in the bay, with uptake in the bay's phytoplankton and contamination of its sportfish. In November 2007, a ship named Cosco Busan collided with the San Francisco – Oakland Bay Bridge and spilled over 58,000 gallons of bunker fuel, creating the largest oil spill in the region since 1996.

In March, 2012 a Bald eagle (Haliaeetus leucocephalus) nest was reported on the northwest arm of Lower Crystal Springs Reservoir and upper San Mateo Creek. This is the first bald eagle breeding pair on the San Francisco Peninsula since 1915, when they nested in La Honda, almost one hundred years ago. The birds were once common in the Bay Area. While visiting Santa Clara County in 1855, physician naturalist James G. Cooper described "a nest of this bird large enough to fill a wagon, built in a large sycamore tree, standing alone in the prairie. Habitat destruction and thinning of eggs from (now banned) DDT poisoning reduced the California state population to 35 nesting pairs at their lowest point. In the 1980s re-introductions began with the Santa Cruz Predatory Bird Research Group and the San Francisco Zoo began importing birds and eggs from Vancouver Island and northeastern California in the late 1980s.