In a March 25, 2018 post, I suggested strong measures to protect salmon populations in the Central Valley. Well, it is time for action number one. Young salmon from last fall’s spawn are pouring down the rivers for the Delta, Bay, and ocean. Hatcheries are about to stock millions of fall-run smolts. Up until last week, young salmon were getting lots of roiling cold water to push them along on their journey. But with a break in the rains snow melt is being trapped in reservoirs, and things are changing. Waters are getting warmer, fish are getting stressed, and predation is up. Sacramento River water levels have dropped over ten feet in the past week, and flow has dropped by half (Figure 1). Water temperatures below Colusa have risen sharply to over 60°F, perfect to stimulate the appetites of striped bass.

Figure 1. River flow at Wilkins Slough on lower Sacramento River, March 26-April 1 2018.

Over the next six warm months, April through September, state water quality standards are supposed to assure salmon of cold 56°F water at Red Bluff and cool 68°F water from there down to the Delta. Outmigrating young salmon need cool water. Newly hatched sturgeon need the cool water in spring. Adult winter-run and spring-run salmon also require the cool water during their spring upstream migration. Adult fall-run salmon need the cool water during their upstream migrationin the late summer and fall.

Until a few years ago, the fish were usually provided what they needed, even in a drought year like 2013 (Figure 2). But that changed during the 2013-2015 drought. In 2015, water temperature reached above 68°F by late April and near 80oF in the summer. (Figure 3). In below-normal water year 2016 and wet water year 2017, low Shasta releases and high water temperatures continued (Figures 4 and 5), to the great detriment of salmon and other native fishes like steelhead and sturgeon.

Now, in spring 2018, conditions have already deteriorated quickly. Water temperatures at Red Bluff now exceed 56°F (Figure 6). Soon lower river water temperatures will reach above 65°F.

The answer is simple. At minimum, Reclamation should keep the flow of the lower Sacramento River at Wilkins Slough near 8000 cfs, as in 2013. Shasta Reservoir is 88% full, 105% of average, and the reservoir will likely fill (4.5 million acre-ft) this spring. Federal managers and contractors probably are forecasting a spring flow of 5000-6000 cfs in the Sacramento River at Wilkins Slough, similar to last year. That would save Reclamation 240,000-360,000 acre-feet in Shasta over two months. But the extra storage would come at the expense of water quality and fish standards, and would mean a lot fewer salmon for the future.

Figure 2. Wilkins Slough gage spring-summer flow and water temperature 2013. Green line is 65°F stress limit for salmon. Red line is water quality standard 68°F for lower Sacramento River.

Figure 3. Wilkins Slough gage spring-summer flow and water temperature 2015. Green line is 65°F stress limit for salmon. Red line is water quality standard 68°F for lower Sacramento River.

Figure 4. Wilkins Slough gage spring-summer flow and water temperature 2016. Green line is 65°F stress limit for salmon. Red line is water quality standard 68°F for lower Sacramento River.

Figure 5. Wilkins Slough gage spring-summer flow and water temperature 2017. Green line is 65°F stress limit for salmon. Red line is water quality standard 68°F for lower Sacramento River.

Figure 6. Water temperature at Bend Bridge near Red Bluff in 2018.

The Merced River salmon population trends follow a similar pattern to those of other Central Valley rivers (Figure 1). Droughts (76-77, 87-92, 07-09, and 13-15) drive the population down. The basic response appears as a two year lag, reflecting the fact that primary mortality comes in the first year of life while living in rivers and migrating to the ocean. Lack of lag in some years likely reflects poor river conditions in late summer and fall when high mortality of adults may occur during their spawning run. The population increases in normal-wet year sequences (82-86, 95-00, and 10-12). The recent better drought performance with good runs in 2016 and 2017 (not shown) likely reflects the practice of trucking most of the Merced Hatchery smolts to the Bay in spring since 2010.

High trucking survival, especially in dry years, is indicative of the real problem facing Merced, San Joaquin, and Sacramento River salmon: poor river habitat conditions downstream of the hatcheries and upper river spawning grounds. One only has to look at water temperatures and flows in the lower San Joaquin River in winter-spring to see that survival conditions are poor in spring, especially in drier years.

With 2017 being a wet year, Merced Hatchery fall run smolts were released in spring at the hatchery outlet instead of being trucked to Bay pens. Approximately 1,250,000 smolts were released in three groups: 4/24, 5/3, and 5/18 (Figure 2). The problem with these releases even in a wet year like 2017 is warm water in the San Joaquin River below the mouth of the Merced River (Figure 3). In dry years like 2015, water temperature are are even higher and occur earlier in spring, with lethal temperatures (>770F) occurring by late April (Figure 4). This is the reason why the hatchery trucks smolts to the west Delta in dry years.

Looking at the most recent tag return data (Figure 5), it appears that trucking to the Bay or west Delta is the best course of action even in wet years like 2011. Because smolts were released at the hatchery in wet year 2017, a poor return would be expected in 2019. A good return is expected in 2018 because smolts were trucked in 2016. Based on these data, trucking would be the best choice in all years.

Merced hatchery smolts are expected to be released later this spring. DFW should truck these smolts to the west Delta. This is particularly important because since 2011, spring Delta exports have been higher than they generally were over the previous three decades. During the Vernalis Adaptive Management Program (VAMP) from 1999 through 2010, April 15 – May 15 exports were restricted to 1500 cfs. Higher spring export levels since the end of VAMP are a real threat to Merced and other Central Valley salmon populations (Figure 6).

Figure 1. Merced River salmon run (escapement to river) 1975-2016. Source: CDFW GrandTab.

Figure 2. Summary of salmon salvage at south Delta pumping plants in winter-spring 2017. Note three Merced hatchery smolt release groups reached the south Delta salvage facilities in early May and continued to be salvaged into mid June. Only 20% of Merced hatchery smolts were tagged, so many of the non-marked smolts at that time were likely also hatchery smolts. Source: http://www.cbr.washington.edu/sacramento/tmp/deltasalvagelength_1521657439_409.html

Figure 3. Water temperature in the San Joaquin River below the mouth of the Merced River at Crows Landing in spring 2017. Red line is high stress level that would lead to poor growth and survival, and high rates of predation. Green line is upper end of optimal growth potential. Yellow line is moderate stress level.

Figure 4. Water temperature in the San Joaquin River below the mouth of the Merced River at Crows Landing in spring 2015, a critically dry year. Red line is high stress level that would lead to poor growth and survival, and high rates of predation. Green line is upper end of optimal growth potential.

Figure 5. Adult hatchery salmon return percentage from tagged smolts released from 2007 to 2013 at the hatchery or trucked to the west Delta. Data Source: http://www.rmis.org/ .

Figure 6. May 2017 salmon salvage at south Delta export facilities with export cfs. Data source: CDFW.