Sonic tags were used by the California Department of Fish and Game to study San Joaquin River salmon migrations through the Sacramento-San Joaquin Delta, to find out if the effects of adverse stream conditions are a significant cause of salmon run decline. It was concluded from the 1965 sonic tagging that (1) the fall-run migrated through the Delta and lower San Joaquin River with ease, reaching the spawning areas two weeks earlier than in recent years, (2) once the San Joaquin River quality and quantity reached suitable levels for salmon, the rate of migration was not affected by gradual changes which occurred in these factors thereafter and (3) pumping water from Tracy into the San Joaquin River above Stockton, to increase the flow past Stockton, increased the numbers of Sacramento River salmon in the lower San Joaquin River.
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