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Figure 1. Major Delta net daily flows (cfs) in mid-December 2017. Map source: USGS. Data sources: USGS and CDEC.<\/p><\/div>\n
For juvenile winter run, spring run, fall run, and late fall run Chinook salmon migrating down the Sacramento River, the risk is obvious.\u00a0 With nearly 40% of Sacramento River inflow diverted at Georgiana Slough and another 30% diverted at Threemile Slough, less than half of the Sacramento River\u2019s inflow to the Delta is reaching the Bay.\u00a0 Of the total Delta inflow, only 45-50% is reaching the Bay.\u00a0 Nearly all the San Joaquin River Delta inflow is being exported.<\/p>\n
Assuming that the young salmon split with the flow, 60% of Sacramento fish are being diverted to the central Delta and near 100% of the San Joaquin fish are lost to the interior Delta.\u00a0 With winter run and late fall run juvenile salmon from the Sacramento River moving into the Delta during the late November storms (Figure 2), there is a high risk that the diverted fish will be lost in the interior Delta.\u00a0 Soon, spring run and fall run fry salmon will be moving into the Delta.<\/p>\n
Under the conditions in the \u201cReasonable and Prudent Measures\u201d required by the National Marine Fisheries Service\u2019s Biological Opinion (BO) for the operation of the state and federal water projects, exports should be reduced when \u201clarge numbers\u201d of juvenile salmon begin entering the Delta (Figure 3).\u00a0 The finding that there are \u201clarge numbers\u201d is based on monitoring of juvenile salmon at Knights Landing and Sacramento.\u00a0 Peak catches in the past month were 3-7 per day (Figure 2).\u00a0 This does not meet the level of 10 per day under which the BO would trigger reducing exports. \u00a0\u00a0However, the trigger dates from a time when the Sacramento River was producing 6 to 10 times more \u00a0juvenile winter run salmon.\u00a0 In the last four years, juvenile production of winter run in the upper Sacramento River near Redding has been at record low levels of 300,000 to 500,000, compared to 3.3 million in 2009 when the BO was published. \u00a0\u00a0\u201cLarge numbers\u201d today are understandably smaller than they were eight years ago.<\/p>\n
Exports should be reduced immediately until outflow to the Bay increases dramatically.\u00a0 January BO limits will require Old and Middle River (OMR) flows near the south Delta export pumps to be no more negative than 5000 cfs.\u00a0 With December OMR flows in excess of -9000 cfs (Figure 4), exports should be reduced now to limit OMR to -5000 cfs or lower per BO Action IV.3 through the remainder of December.<\/p>\n
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Figure 2. Catch of unmarked older Chinook juveniles (likely winter run and late fall run) at Knights Landing and Sacramento in fall 2017. Data from CDFW and USFWS surveys as reported by www.cbr.washington.edu\/sacramento\/<\/a><\/p><\/div>\n Figure 3. Excerpt from p. 652 of NMFS BO 2009.<\/p><\/div>\n Figure 4. OMR flows in south Delta. Source: https:\/\/www.usbr.gov\/mp\/cvo\/vungvari\/OMR_Dec2017.pdf .<\/a><\/p><\/div>\n","protected":false},"excerpt":{"rendered":" With a potentially record-low rain total for December, the federal and state water projects are cutting reservoir releases but keeping up exports from the Delta, causing great peril to Central Valley salmon.\u00a0 Figure 1 summarizes Delta conditions as of mid-December. … Continue reading ![\"\"](\"http:\/\/calsport.org\/fisheriesblog\/wp-content\/uploads\/2017\/12\/image3-1024x558.jpeg\")
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