Interagency Ecological Program: Summer Townet Survey for Young Pelagic Fishes in the San Francisco Estuary

The Interagency Ecological Program’s (IEP) Summer Townet Survey (STN) is a long-term effort to monitor the annual recruitment success of young pelagic fishes in the upper San Francisco Estuary (California, United States). Conducted by the California Department of Fish and Wildlife (CDFW) since 1959, STN has sampled fixed locations from Eastern San Pablo Bay to Rio Vista on the Sacramento River, and to Stockton on the San Joaquin River; and a single station in the lower Napa River. The study area was expanded in 2011 to include the Sacramento Deep Water Ship Channel (SDWSC) and Cache Slough (CS). Currently, 40 stations are sampled as a “survey” every other week June through August for 6 surveys. A conical net, lashed to a fixed metal “D” frame, is pulled obliquely through the water column 2 to 3 times at each station. All fish and macro-invertebrates are identified and enumerated from each tow, with fork lengths (mm) of the first 50 of each fish species also recorded. Fish catch, length-frequency, and catch-per-unit-effort (CPUE) among stations is available with data visualization tools on the study website for all species (https://wildlife.ca.gov/Conservation/Delta/Townet-Survey). Data collected at historic 31 stations are used to calculate annual relative abundance indices for age-0 Striped Bass (Morone saxatilis) and Delta Smelt (Hypomesus transpacificus). The remaining 9 stations are sampled to expand our sampling range further upriver and increase our understanding of larval and juvenile fish abundance and distribution in the lower Napa River and the North Delta. A meso-zooplankton net targeting copepods and cladocerans is also used in parallel to assess fish food resources at each station and a subset of the fish collected are retained for diet analysis by CDFW researchers (beginning 2005, see STN and FMWT zooplankton data on EDI). The STN also measures habitat conditions via water temperature (°C), water clarity (Secchi disk depth in cm), Turbidity (NTU) and specific conductance (µs/cm). Historically, STN began in response to the development of Central Valley Project pumping plants exporting water from the South Delta. STN continues to monitor fish abundance and distribution in relation to water diversions, for the operation of the Central Valley Project and the State Water Project, and management flow actions to improve summer-fall habitat conditions. Managers and researchers use the data collected by STN to inform decisions and improve our understanding of the health of the upper San Francisco Estuary.