A new study from the Center for California Water Resources Policy and Management released last week provides a fresh perspective on the endangered Delta Smelt. The tiny fish at the epicenter of the Delta ecosystem debate has continued to decline despite nearly two decades of efforts to protect it. Resource managers and policymakers should take note of the study’s findings, the important insights it provides, and the new pathway identified for recovery of the species.
The peer-reviewed scientific study, published in Environmental Management, identifies food availability as well as predation and competition from invasive species as the key factors contributing to the decline of the delta smelt. The study relied on the concept of “limiting factors” or the recognition that while multiple factors may influence the status and trend of a species, just one or two operate to control population numbers and their directional trend. According to the study, the limiting factors impacting smelt survival are the availability of zooplankton as a food source, and predation and competition from non-native, invasive Mississippi Silverside fish.
Having identified the two limiting factors that are harming the performance and recovery of the species, a more effective approach to recovery can be implemented. A new focus is desperately needed. State and federal resource managers have previously expended significant water resources intended to benefit the Delta Smelt but that approach hasn’t worked. The study supports a conservation strategy that relies less on water outflow, focusing instead on actions designed to address the limiting factors such as restoration of tidal marshlands and minimizing opportunities for predation.
New approaches and actions, such as the ones identified by the study are desperately needed in the Delta. By looking at the Delta through the lens of limiting factors, we can see old problems in a different – maybe simpler – way. This different way of focusing will lead to better management of the complex ecosystem. Sound science can guide these actions, but resource managers must be willing to try new approaches to improving the ecosystem. Unless and until that happens, we will remain on the current path of continued species decline and water supply disruptions.