Chinook salmon spend most of their lives in salt water, but they hatch, spawn, and die in freshwater streams. While they can travel many hundreds of miles to spawn, they always return to the very spot where they were hatched.

Four separate runs of chinook salmon pass through Golden Gate each year, in the spring, fall, late fall, and winter. After their journey, female fish lay eggs in gravel nests for the males to fertilize. The adult fish then die, leaving the "small fry" to make their way back to salt water, renewing the cycle. The completion of Shasta Dam in 1945 made it impossible for the winter-run chinook to return to their traditional spawning ground upstream from the dam, and so the fish now spawn primarily in the main stem of the Sacramento River, between Redding and Tehama, just below Red Bluff Diversion Dam. Young fish spend time in the bay before moving out to the ocean.

Because they travel such distances over the course of their lives, the chinook are exposed to a variety of environmental factors. That makes it difficult for researchers to pinpoint the precise causes of population trends (an upswing in population could be the result of conditions in any of several parts of the ecosystem). On the other hand, it also makes the chinook a good bellwether for the health of the entire system.

The Winter Run's Health
The winter run is the most imperiled of the Bay-Delta's four runs of chinook salmon. (Salmon runs are named for the time of year when the fish leave the ocean and move upstream in preparation for spawning.) The winter-run salmon was listed as a threatened species under the federal Endangered Species Act in 1990 and reclassified as endangered in 1994. Many factors have contributed to the decline of these salmon, including:

• Warm-water releases from Shasta Dam. As the reservoir was drawn down during the last drought, the remaining water was heated by the sun to temperatures that killed salmon eggs and young fish downstream.
  
  
• Loss of habitat. Shasta Dam blocks access to most of the winter run's historic spawning habitat. Habitat losses in the Sacramento River and in the bay and delta have also hurt the salmon.
  
  
• Water diversion. Two massive state-run water projects completed around 1970 divert huge quantities of water from the Sacramento-San Joaquin Delta to agricultural and residential uses elsewhere. Salmon suffer from the lower levels of remaining freshwater in their habitat and from the increased water temperature resulting from those lower levels.
  
  
• Red Bluff Diversion Dam. This dam on the Sacramento River pumps water from the river to agricultural canals. Fish are often sucked in here and killed. In addition, the pumps at some agricultural diversions have no fish screens, while others are inadequately screened.
  
  
• Mine drainage. Contaminants from the abandoned Iron Mountain Mine harm the winter run.
  
  
• Agricultural pollution. Runoff from agricultural fields contains pesticides and fertilizers that harm the chinook.
  
  

Weather and ocean conditions also play an important role in determining winter-run populations, as does fishing pressure. But the impact of sport and commercial fishing on chinook has been greatly reduced by restrictions on the total take of fish and seasonal closings to protect the winter run.

Undoing the Damage
In recent years, significant progress has been made in the effort to bring back the Bay-Delta's salmon. For example, state and federal agencies have finally adopted standards designed to protect the Bay-Delta and its fisheries from the impacts of water diversions. Some water has been dedicated to providing needed freshwater flows for salmon recovery, and a few small dams have been removed from spawning streams. In addition, fish screens have been installed on pumps at several agricultural water diversions. Finally, the CALFED Bay-Delta Program and other efforts have restored some critical habitat for young salmon on Central Valley rivers, in the delta, and in the bay. These efforts have contributed to modest population increases in recent years. More work in each of these areas will be needed, however, to restore healthy populations.

For example, greater flexibility is still needed to reduce the volume of water pumped from the delta at critical times to protect migrating fish. Several obsolete dams still need to be removed to open up spawning habitat. And, given the loss of habitat in the Central Valley and in the bay, much more habitat restoration will be needed to meet the needs of salmon as they migrate through this ecosystem.

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