The fall midwater trawl index of spawning adult longfin smelt in 2019 was below expectations for a wet year (Figure 1). In a January 8, 2020 post, I foreshadowed the reduced fall spawner index for 2019, and suggested a grim outlook for the future of the population. In addition, high December 2019 Delta exports forced more spawning upstream into the Delta, increasing the likelihood of larval entrainment into the south Delta export pumps.
January 2020 larval smelt surveys (Figures 2 and 3) indicate that the production of longfin smelt larvae was indeed low. However, modest improvement occurred in both 2018 and 2020 compared to recent drought years (2015 and 2016). Application of the Fall X2 Delta outflow prescriptions in wet years 2017 and 2019 (higher outflow in Figure 4) likely contributed to the higher numbers of longfin larvae in the Bay in January 2018 and January 2020.
The numbers of larvae in 2018 and 2020 were still well below those in January 2012 (Figure 2), when the spawning population (2011) was much higher. Also, December exports in 2011 were much lower than in 2019 (Figures 5 and 6).
In summary, the benefit of the Fall X2 Bay Delta water quality standard has shown up again in the Larval Smelt Survey in January 2020. High December south Delta exports continue to hinder recovery of the longfin smelt population.