Stockton Fish and Wildlife Office
Pacific Southwest Region

female chinook salmon iconAFRP OVERVIEW: BACKGROUND

450 miles long and 50 miles wide, California's Central Valley contains one-sixth of the irrigated land in the United States and hosts two major river drainages Sacramento and San Joaquin which meet and drain into the Pacific Ocean through the San Francisco Bay. Authorized by President Franklin D. Roosevelt in 1935, the largest reclamation endeavor ever undertaken, the Central Valley Project (CVP) was viewed to be the remedy for the imbalance of environmental impacts associated with power and water production in the Central Valley. The goal of the CVP was a water transportation network to supply irrigation water from dams and reservoirs in the Sacramento River to the water limited, but highly arable lands of the San Joaquin River Basin. Covering an area over 400 miles long and up to 100 miles wide, the CVP never finished as planned. Ecological impacts to migratory salmon and controversies over dam construction prevented further construction and led to the passage of the CVPIA in 1992.

Since settlement of the Central Valley in the mid-1800s, populations of native anadromous fishes, in particular, Chinook salmon (Oncorhynchus tshawytscha), steelhead (O. mykiss), white sturgeon (Acipenser transmontanus), and green sturgeon (A. medirostris) have declined dramatically. These declines have been so dramatic that several species are currently in danger of extinction. At present, winter-run Chinook salmon are listed as endangered and spring-run Chinook salmon and steelhead are listed as threatened under both the federal and state Endangered Species acts, and all other races of Chinook salmon are considered candidates for listing by the National Marine Fisheries Service.

Habitat degradation is the primary cause of these declines. Hydraulic mining for gold was the first major human activity that resulted in large-scale habitat degradation due to sedimentation and diversion of water in many Central Valley streams. Hydraulic mining was prohibited in 1894, but habitat degradation still continues today. Habitat quantity and quality have declined due to anthropogenic modifications to natural hydrologic regimes by construction of dams and other diversions and barriers to migration, levees and other flood control infrastructure, and gravel mining. Major alterations to watersheds such as these isolate spawning habitat and can lead to other effects such as elevated water temperatures, low available oxygen, sedimentation problems and water pollution. Although the effects of habitat degradation on fish populations were evident by the 1930s, the decline for most anadromous fish species has only accelerated since completion of major water project facilities to meet the increasing demands for Central Valley water.

Other factors that have adversely affected natural stocks of anadromous fish include overharvest by commercial fisheries, illegal harvest, competition and loss of genetic integrity from hatchery produced fish, and introduction of competitors, predators and diseases. Natural events such as drought and poor ocean conditions, such as El Niño, affect water flow and temperature and can severely affect populations. Historically, populations in habitats not so heavily impacted by human activity typically recover within a few years after natural catastrophic events. However, the decline of anadromous fish populations in the Central Valley has continued through these natural cycles of beneficial and adverse natural conditions, indicating the need for human intervention to improve fish spawning and rearing habitat, the identified ecological crux for continued survival.

American shad (Alosa sapidissima) and striped bass (Morone saxatilis), the two non-native anadromous species identified for restoration by the CVPIA, were introduced into the Sacramento-San Joaquin system in the 1870s. Both species supported valuable sport and commercial fisheries throughout much of this century, but California Department of Fish and Game (CDFG) data indicate that populations have declined since the mid-1960s. Other diadromous fishes in Central Valley waters include threespine stickleback (Gasterosteus aculeatus) , brown trout (Salmo trutta), and lamprey (Lampetra spp.). However these are not identified in Title 34 of CVPIA and not included in the AFRP restoration goals.

Expanding the accessible range of habitat and improving the quality of fish habitat are important, key features of AFRP sponsored activities to restore natural stocks of anadromous fish. The AFRP coordinates closely with CALFED and many other agencies and programs focused on restoration of Central Valley streams and the Bay-Delta ecosystem. The AFRP, much like CALFED, has adopted an “adaptive management” approach towards ecosystem restoration.

Last updated: August 24, 2011