Fig 1.
Map of the upper San Francisco Estuary depicting the sites at which Delta Smelt was collected, their region classifications, and the locations of temperature loggers.
DWSC = Sacramento Deep Water Ship Channel, LSZ = low salinity zone, SR = Sacramento River. Blue colored region indicates water bodies (perennially wetted area) in the estuary and purple colored region denotes the extent of Yolo Bypass floodplain that can be inundated during flooding events.
Table 1.
Number of juvenile Delta Smelt analyzed for otolith microstructure in this study, sorted by region and year.
All fish collected at the Yolo Bypass were genetically confirmed as pure Delta Smelt. Cache is Cache Slough region, DWSC is Sacramento Deep Water Ship Channel, LSZ is low salinity zone, SR is Sacramento River, and Yolo is Yolo Bypass. Numbers in parentheses indicate the number of fish that were also processed for diet analysis, followed by the number of fish with stomach content intact.
Fig 2.
Catch per unit effort of Delta Smelt in the Yolo Bypass compared to elsewhere in the San Francisco Estuary: a.) Catch per hour of Delta Smelt in the Yolo Bypass rotary screw trap sorted by calendar year, life stage, and whether fish was genetically confirmed as Delta Smelt. b.) Abundance index from the 20-mm Survey [45]. c.) Abundance index from the Summer Townet Survey [43].
Fig 3.
Comparison of juvenile Delta Smelt size between the Yolo Bypass (red) and elsewhere in the San Francisco Estuary (from 20-mm Larval Survey in light blue, from Summer Townet Survey in dark blue). Note that the YBFMP does not record fish with fork length under 25 mm. Red dashed line represents the 25 mm fork length lower limit cutoff for the YBFMP. Areas between the vertical black dotted lines represent the months of May and June, the months of focus for this study.
Fig 4.
OLS regression results demonstrating the linear relationship between fish age and length in our dataset.
Each dot represents a single individual fish and shaded region represent the 95% prediction interval of the regression model.
Fig 5.
Box plots showing G (individual growth rate) and hatch date for juvenile Delta Smelt used in this study by region and year.
Color indicates the water year classification for the year (e.g. critically dry, dry, wet, etc.). Region codes are as follows: Cache = Cache Slough region, DWSC = Sacramento Deep Water Ship Channel, LSZ = low salinity zone, SR = Sacramento River, Yolo = Yolo Bypass.
Fig 6.
Estimated mean a.) individual growth rate and b.) hatch date by region based on our GLMM. Error bars are the 95% confidence intervals for each region. Letters above error bars denote grouping with significant differences at α = 0.05 after Bonferroni-Holm correction (e.g. A and B regional difference was statistically significant, and as such regions labeled AB were not statistically different from regions labeled as either A or B). Region codes are as follows: Cache = Cache Slough region, DWSC = Sacramento Deep Water Ship Channel, LSZ = low salinity zone, SR = Sacramento River, Yolo = Yolo Bypass.
Table 2.
Parameter estimates for the GLMMs used to evaluate if G and hatch date for Delta Smelt vary by region of capture.
Cache = Cache Slough region, DWSC = Sacramento Deep Water Ship Channel, LSZ = low salinity zone, SR = Sacramento River, Yolo = Yolo Bypass.
Table 3.
Summary of diet composition information from juvenile Delta Smelt collected in the Yolo Bypass Toe Drain (N = 42).
%N is percent of prey taxon by number, %W is percent of prey taxon by weight, %FO is frequency of occurrence, and IRI is index of relative importance.
Table 4.
Summary of February-May Delta Smelt-relevant temperature metrics comparing the Yolo Bypass Toe Drain, lower Sacramento River near the city of Rio Vista, and the confluence between Sacramento and San Joaquin Rivers (Sac-SJR confluence) for the duration of the study period.
Values shown are mean temperature from February to May for each year, the number of spawning days available for Delta Smelt for each period based on temperature (15–20°C), and the median day of year for each spawning period (where January 1st = 1).