Potential interactions between urban runoff and decline of pelagic fishes

Urban runoff has been identified as one of many potential drivers of the decline of pelagic fishes in the upper San Francisco Estuary. Participants in this working group will use an ecological risk-assessment approach to address potential chemical influences on delta smelt, longfin smelt, threadfin shad, and striped bass in urban environments. Housing and transportation infrastructure drains into spawning and nursery areas for these species. Three of the species spawn during months in which rain typically falls, leading to substantial urban storm runoff. Shifts in the pesticides applied in urban environments, from organophosphates to synthetic pyrethroids and, more recently, phenyl pyrazoles, have coincided with steep declines in pelagic fishes. These newer pesticides have relatively long persistence times, and may be transported in sediments into the fishes’ habitat. There is potential for relatively high toxicity to prey items for larval fishes as well as to early life stages of the fishes.