Pelagic Organism Decline Overview

The Interagency Ecological Program (IEP), a consortium of nine state and federal agencies, has been monitoring aquatic organisms and water quality in the San Francisco estuary for decades. Since late 2004, scientific and public attention has focused on the unexpected decline of several pelagic (open-water) fishes (delta smelt, longfin smelt, juvenile striped bass, and threadfin shad) in the freshwater portion of the estuary known as the Delta. This decline has collectively become known as the Pelagic Organism Decline (POD). In 2005, the IEP formed a multi-agency POD Management Team tasked with designing and managing a comprehensive study to evaluate the causes of the decline and to synthesize and report the results. The causes under investigation include stock-recruitment effects, a decline in habitat quality; increased mortality rates; and reduced food availability due to invasive species.

POD Synthesis Overview

Abundance indices calculated by the Interagency Ecological Program (IEP) suggest recent marked declines in numerous pelagic fishes in the upper San Francisco Estuary (the Delta and Suisun Bay). Although several species show evidence of long-term declines, the recent low levels were unexpected given the relatively moderate winter-spring flows of the past several years.

Our initial conceptual model included three general factors that may be acting individually or in concert to lower pelagic productivity: toxins, invasive species, and water project operations. The overall approach for 2005 was based on a “triage” model to identify the most likely causes, and to assign priorities to projects on the basis of where funds and resources can be best used. The 2005 work fell into four general types: an expansion of existing monitoring (four expanded surveys); analyses of existing data (nine studies); new studies (six studies); and ongoing studies (four studies). This document represents a progress report for the 2005 work completed to date. Because most of the studies are still in progress, the 2005 findings should be considered tentative and this report will be updated as input and information becomes available.

For a more detailed look at the Synthesis Report, please read the full document:

IEP Synthesis of 2005 Work to Evaluate the Pelagic Organism Decline (POD) in the Upper San Francisco Estuary

Supporting Documents