On March 8, I posted some questions about the San Joaquin salmon restoration program and its upcoming release of hatchery smolts. On March 18, CDFW released 105,000 hatchery smolts into the San Joaquin River near Merced.1
The release coincided with the modest peak in annual San Joaquin River flow (Figure 1). Delta outflow peaked near 70,000 cfs at that time. Water temperatures were also below the stressful level of 68°F (20°C) (Figure 2). Smolt releases in the past two years did not have such good conditions, and few survived to reach the Delta. In contrast, in the week following this year’s release nearly 500 of these marked Spring-Run smolts have shown up in fish salvage at the South Delta export facilities , a clear indication that many survived to the Delta. The salvage numbers also indicate the released smolts had to take a tough route through the Delta with no assurance that they were successful in reaching the Bay even under the high wet year Delta outflows. It remains to be seen how well these smolt releases from the past three years fare in terms of survival to the Bay (Chipps Island Trawl Survey) and Ocean (coastal fisheries returns). I stand by my recommendation of barging the smolts to the Golden Gate, which would assure 99% survival to the Ocean.
Figure 1. Hourly flow in the San Joaquin River near Vernalis from March 5 to April 4, 2016.
Figure 2. Water temperature (Deg F) in the San Joaquin River below Merced from March 5 to April 4, 2016.