In a June 1 post, I wrote of an apparently strong year class of striped bass developing in 2016.  This analysis was based on May surveys.  I suggested then the comeback could fall short after higher exports began in June.

The results of the two DFW 20-mm Surveys for June are in, and these results indeed show a sharp decline in the densities of juvenile striped bass between early and late June (Figure 1), coincident with a rise in south Delta exports over the month (Figure 2).  Some of the greatest changes occurred in the interior Delta (900 stations), where the effect of exports would be greatest.

The late June densities, though higher than 2014 and 2015, are consistent with densities over the previous decade of striped bass decline and are lower than the prior decade of striped bass recovery.  With the demise of the Delta smelt population, it may be appropriate to consider striped bass once again as the Delta’s “canary-in-the-coal-mine.”

Figure 1. Striped bass juvenile density in the Delta in June 2016 20-mm surveys. The 700 stations are from the lower Sacramento River channel of the west and north Delta. The 800 stations are from the lower San Joaquin River channel of the west and central Delta. The 900 stations are from interior Delta channels. ( http://www.dfg.ca.gov/delta/data/20mm/stations.asp )

Figure 2. Reverse flow in Old and Middle Rivers in central Delta in June 2016. Reverse flows are representative of the direct effects of south Delta exports on central Delta channels. The survey periods of the two DFW 20-mm surveys are shown.