The California Department of Fish and Wildlife released spring-run and fall-run salmon smolts raised at the Feather River Hatchery into the lower Feather River from late March to early May 2018. The initial spring-run releases were accompanied by a flow pulse up to 14,000 cfs into the lower Feather River.1 The early May release2 of fall-run was made without the benefit of a flow pulse.
Past performance of hatchery spring-run smolt releases is shown in Figure 1. The 2011 successful smolt release was accompanied by 8,000-17,000 cfs Oroville Dam flows (Figure 2) and wet year conditions in the Bay-Delta. The 2012 modestly successful smolt release was accompanied by a 3000 cfs flow pulse. The 2007 to 2009 smolt releases also had an accompanying 3000-5000 cfs flow releases, but flows that followed fell to 1000-2000 cfs. There was no flow pulse in 2010.
The early April 2018 flow pulse in the Feather River was followed by falling flows (14,000 cfs in early April down to 1000 cfs flow in late April – Figure 3). The latest release of fall-run smolts on May 2 was made near the mouth of the river because of low Feather River flows. Flows in the Sacramento River were also low (less than 10,000 cfs – Figure 4), and water temperatures were marginal at 65°F. The evidence summarized in Figures 1 and 2 suggests that smolts should be trucked to the Bay in non-wet years without strong flow pulses. Survival would be further increased if the smolts are barged from the mouth of the river.3
We can expect good survival from the earlier releases that were accompanied by flow pulses and poor survival from the early May release without a flow pulse. The latter release should have been trucked to the Bay.