A historical understanding of the decline of chinook salmon in California's Central Valley may help conservation biologists set goals for restoring this formerly prodigious population, UC Davis researchers say. Once a substantial food source for early Native Americans and Euro-American settlers of the region, chinook salmon were decimated during the past century through overfishing, dam construction and mining-related stream degradation. Research associate Ronald Yoshiyama and Professor Peter Moyle, both of UC Davis' wildlife, fish and conservation biology department, took a comprehensive look at historical records. Better estimates of previous chinook salmon numbers and a close look at factors linked to their decline may guide future efforts to restore the depleted salmon runs, the researchers say. Based on early commercial catch records, at least 1 million to 2 million spawners -- fish old enough to reproduce -- once filled rivers and streams annually in four seasonal runs during the fall, late-fall, winter and spring. Today, only the fall run is considered stable; the other runs are threatened with extinction. But even the fall run is at risk. In the Sacramento River basin, wild chinook salmon numbers are greatly influenced by hatchery fish. While the hatcheries contribute to overall salmon production, potential negative effects include competition between wild and hatchery juveniles, disease transmission and loss of genetic diversity in wild populations. "We assumed that early hatcheries helped restore the number of chinook salmon in this region," Yoshiyama said. "Now we realize that we're really doing band-aid operations with hatcheries." "Restoration efforts have been based on 20-to-30-year-old estimates of previous salmon numbers," Moyle said. "The purpose of this research was to set a more accurate baseline for restoration efforts." Study results were published recently in the North American Journal of Fisheries Management.