Climate Change Projections on Management-Relevant Scales: Coupling Local-Scale Models of Water Temperatures to Maturation of Delta Smelt

Delta Smelt, a species endemic to the San Francisco Estuary, is of significant interest because actions taken to protect the species can affect water management in California.  Reproduction of this primarily annual species is dependent on maturation of individuals within a single year. We defined the “maturation window” as the time period between the cessation of stressful summer-fall water temperatures (≥24°C) to the initiation of spawning in the early spring at 15°C. We then calculated trends in the Julian date of the initiation of the maturation window and duration of the maturation window for four scenarios of climate change for 2010-2099. Increases in the number of days with mean daily water temperature ≥24°C during the fall and earlier initiation of spawning resulted in significant declining trends in decadal medians of the duration of the maturation window for 14 of 15 sites evaluated for all four scenarios (P<0.05, Mann-Kendall test). For the most severe scenario, this translates to a shortening of the maturation window of about 40 to over 80 days over the century. It seems likely that this reduced time for growth and maturation would have a negative effect on fecundity and therefore on viability of the Delta Smelt population.