In an October 2018 post, I discussed the record low Sacramento River1 2017 adult fall-run Chinook salmon run and juvenile fall-run production index from winter-spring 2018. Both record lows were indications that something had gone wrong for brood year 2014. I also forecasted a poor adult run in fall 2018. The latest information on salmon runs for 2018, recently published by the California Department of Fish and Wildlife, indicates the 2018 fall run was indeed also poor (Figure 1). The run size in 2018 was 8980 (5th lowest in the record), as compared to 1822 in 2017, and 29,966 in 2014.
Despite a normal water year in winter-spring 2016 in the Sacramento River, the hangover from the critical 2013-2015 water-years drought (low reservoir levels) provided harsh conditions for brood year 2015 fall run that led to the poor adult run in 2018:
- Poor river conditions due to low streamflows during the spawning run in summer and late fall 2015 (Figure 2 and 3).
- Poor egg-embryo incubation in gravel redds due to low streamflow in late fall 2015 and early winter 2016 (Figure 2).
- Poor fry survival from low winter streamflows (February and early March) and poor smolt survival from low late spring streamflows (late April and May) in 2016 (Figure 3).
In addition, most of the 10 million Coleman Hatchery smolts raised for brood year 2015 were released at the hatchery in lower Battle Creek from April 7 to April 29, 2016, under sharply declining streamflows (Figure 3) and rising water temperatures in the lower Sacramento River (Figure 4). Their contribution to the 2018 spawning cohort was similarly low. Of the 10 million smolts released, only 14,000 adults returned to the upper river, as compared with 84,000 in 2012.
Based on the spawner recruit model, the 2018 fall run of 8980 adult salmon could have been three times as high or higher (similar at least to 2012 or 2014) if not for poor river flows and associated high spring water temperatures that exceeded water quality standards.
The prognosis for the upcoming 2019 run is mixed, but the run should show improvement. Early indications are good,2 despite very low numbers of spawners in fall 2016 (red 16 in Figure 1). Water year 2017 was wet (19 will be blue in Figure 1). Coleman Hatchery’s released 10-million smolt to the upper river in April 2017 under optimal conditions. There were stressful warm water (>20oC) and low flow conditions in July-August 2016 early in the 2016 spawning run (Figure 5), as well as low and sharply dropping flows in the fall spawning season that likely caused some redd dewatering and low egg/embryo survival. Maintaining less than stressful water temperature during the early run in summer will be important; conditions are already marginal during late spring when winter-run and spring-run adults are migrating (Figure 6). Flows in the 10,000-14,000 cfs range may be necessary to maintain water temperatures at or below 20oC through the summer. With Shasta Reservoir full and an abundant snowpack, that should be readily achievable.
Hopefully, the 2019 run can approach that of 2012 (green 12 in Figure 1) for that low level of spawners (09 and 16 were similar). The results for summer coastal and river fisheries will be the next indicator of success for the 2019 fall-run salmon.
- Keswick Dam to Red Bluff mainstem river. ↩
- https://www.sanluisobispo.com/news/local/article230993873.html https://cdfgnews.wordpress.com/2019/03/01/slightly-improved-forecast-for-californias-2019-ocean-salmon-season/ ↩