Quantifying relative risk of collapse for Delta fish populations

Jonathan Walter (Project Contact)
Levi Lewis
Jim Hobbs
Andrew Rypel
Project Description

Widespread collapse of native fisheries in the Sacramento-San Joaquin Delta is an existential threat to fisheries management and water policy in California. However, most research and management attention is focused on species already known to be in severe decline. This strategy may be sub-optimal, costly, and tends to fail to restore species to former abundances. In contrast, intervention prior to collapse is less costly and more effective, but requires tools for detecting early indicators of population decline. The central aim of this project is to develop and share tools for identifying populations of Delta fishes vulnerable to collapse. Further, we propose identifying critical variations in environmental conditions linked to potential collapse, thereby elucidating management actions with a high probability of preventing irreversible change.  

The ability to assess risk of impending regime shifts associated with stressors is increasingly vital to supporting proactive natural resource management. Yet identifying populations susceptible to collapse is a longstanding challenge in conservation biology. Indeed, alternate stable states of ecological systems, including the thresholds and breakpoints that occur between them, have been investigated since at least the 1970s. Traditionally, identifying susceptible populations has required detailed, species-specific population models, precluding their application to a suite of many understudied species. However, recent developments in ecological theory on resilience and regime shifts, and their successful application in empirical settings, offer new possibilities for enhanced predictions. We are applying these statistical approaches to long-term monitoring datasets in the Sacramento-San Joaquin Delta and developing sharable tools for early identification of fragile fish populations vulnerable to collapse.

Project Status