Pelagic Organism Decline Overview
In the last few years, the abundance indices calculated by the Interagency Ecological Program (IEP) Fall Midwater Trawl survey (FMWT) and Summer Townet Survey (TNS) show marked declines in numerous pelagic fishes in the upper San Francisco Estuary (the Delta and Suisun Bay) (IEP 2005). The abundance indices for 2002-2004 include record lows for delta smelt and age-0 striped bass and near-record lows for longfin smelt and threadfin shad.
In contrast, the San Francisco Bay Study did not show significant declines in its catches of marine/lower estuary species. Based on these findings, the problem appears to be limited to fish dependent on the upper estuary. In response to these changes, the IEP formed a Pelagic Organism Decline (“POD”) work team to evaluate the potential causes.
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: