Living in a Dynamic Environment: Variability in Life History Traits of Age‐0 Splittail in Tributaries of San Francisco Bay

Abstract

AbstractSplittail Pogonichthys macrolepidotus is a relatively large cyprinid endemic to the San Francisco Estuary watershed. During late winter and early spring, splittails migrate from the estuary to upstream rivers and floodplains for spawning. During 2002 and 2003, we examined the diet composition, muscle stable isotope signatures (δ13C and δ15N), and growth rates of age‐0 splittails in the four primary rivers used for spawning. Overall, we found substantial variability in all three traits in spatial and temporal comparisons. Age‐0 splittails consumed a variety of prey taxa, consisting almost exclusively of aquatic invertebrates, larval stages of chironomids or copepods generally being the most common. We found that the δ15N and δ13C signatures of age‐0 splittails significantly varied spatially and temporally (δ15N range = 6.1‐19.6‰; δ13C range = −36.3 to −17.5‰). Environmental conditions, namely flow and how it manipulates habitat connectivity, appeared to affect δ13C. Age‐0 splittails exhibited substantial variability in growth rate both spatially and temporally. However, this variability was not associated with diet composition or stable isotope signatures, suggesting that food availability and physical habitat conditions were important factors affecting growth rates during our study.