One way to effectively increase the California coastal salmon population is to increase survival of Chinook salmon smolts released by the three large Sacramento Valley hatcheries. These three hatcheries produce nearly 30 million fall-run smolts a year and account for 70-90% of California’s ocean and river fishery catch. A one percent smolt survival leads to 300,000 adult returns to the fisheries and escapement to spawning rivers. Doubling survival to two percent would increase returns to 600,000 adults. With survival at or below one-half percent in recent drought years, returns have fallen to near 100,000.1
How can we get survival back to one or even two percent or higher? Fortunately at least a quarter of the smolts are tagged to allow estimates of their survival and contributions to fisheries and escapement back to spawning rivers. Survival estimates are now available for hatchery smolts released up to 2013. Figures 1-3 show a summary of survival from the three largest hatcheries for salmon brood years 2008-2012 (smolt releases from 2009-2013). I drew the following conclusions from the figures:
- Releasing smolts in the spring of drought years in the rivers near the hatcheries provides only about a half percent survival in drought years (release years 2009 and 2013). Survival improves to 1-3 % in wetter years (release years 2010 and 2011), likely a consequence of better transport flows, lower water temperatures, and lower predation because of higher turbidity.
- Poor ocean survival (2008-2009, and 2014-2015) likely contributes to poor survival (percent returns) for those brood years rearing in the ocean under poor conditions.
- Transporting the salmon smolts via truck to San Francisco Bay for release into acclimation pens markedly increases survival in dry and wetter years into the 1-3% range. The benefit appears smaller in the wetter years, but remains significant and substantial. The Feather and American state hatcheries continue transporting the bulk of their smolts in recent years, while the federal Coleman hatchery has greatly reduced the practice because of apparent higher straying rates.
- The program of releasing Feather smolts to coastal bay pens sharply increases returns to coastal fisheries. However, the threat of these fish straying to coastal streams with different genetic stocks now limits this practice.
- Lastly, barging fish from near their hatcheries to the Bay shows much promise. Barging may triple survival in drier years when survival is one percent or less, and may reduce straying. A multiyear study of barging is currently underway.
In conclusion, adult salmon stocks in coastal waters continue to benefit from transporting smolts to Bay net pens. Further benefits may derive from barging the smolts 100 to 200 miles to the Bay. Potential benefits of barging over trucking include higher survival and reduced straying. Release of hatchery smolts directly to Sacramento Valley rivers near the hatcheries provides minimal survival especially in drier years. Increasing survival factors like augmenting flow releases from reservoirs at the time of river hatchery releases may improve survival, but trucking and barging appear necessary to keep ocean and river fisheries afloat in the short term.