REDDING, Calif. -- About 75,000 young Chinook salmon have died while being hauled in tanker trucks from a federal fish hatchery in Anderson to San Pablo Bay near Vallejo.

The hatchery's manager suspects an oxygen level problem killed about 40 percent of the 180,000 fish in the tankers.

Monday's delivery was the first of 18 planned in the next several weeks as part of an effort to revive the state's salmon population, which has suffered a severe decline in recent years.

Officials hope more salmon will survive by being trucked to the ocean instead of trying to reach it by navigating the delta, where they must survive the state's water pumps.

U.S. Fish and Wildlife Service spokeswoman Alexandra Pitts says scientists plan to perform autopsies on some of the dead Chinook salmon smolts to determine the cause of death.