Patterns and predictors of condition indices in a critically endangered fish

Condition indices are key predictors of health and fitness in wild fish populations. Variation body condition, therefore, can be used to identify stressful conditions that may impact endangered species, such as California’s endemic Delta Smelt (Hypomesus transpacificus McAllister, 1963). Here, we examined spatiotemporal variation the condition > 1600 collected over nine years (2011–2019), a period characterized by tremendous variability hydrodynamic water quality conditions. The population exhibited low hepatosomatic index (HSI) factor (CF) during September/October/November (fall), both declined nine-year study fall. HSI was positively correlated with indicators pelagic productivity (e.g., Chlorophyll a, zooplankton biomass, proximity tidal wetlands), whereas CF negatively temperature, peaking at relatively cool 10–13 °C. In sum, seasonal interannual corresponded most strongly little correlation freshwater outflow. Management actions increase productivity, restore freshen productive wetlands late summer-fall, reduce temperatures overall likely benefit and, population.