Interagency Ecological Program: Fish catch and associated water quality for the Fall Midwater Trawl Survey, Sacramento-San Joaquin Delta, 1967-2024

Most stations no longer sampled occur in South and Central San Francisco Bay (1968-1979), with others located in San Pablo Bay and upstream into the Delta. There are catch records for stations that were sampled only once. Data users are encouraged to look at station frequency over time to understand when and where sampling occurred.

Sampling takes approximately 14 days per month to complete. Historically, FMWT sampling occasionally began as early as July (1972) or August (1968-1973, 1993-1994, 1996-1997) and sometimes continued past December to March (1968-1973, 1978, 1991-2001) or beyond (1992-1995). The Spring Midwater Trawl (SMWT) was a modified survey created to continue sampling January-March to track movements of mature adult delta smelt from 1991-2001.

SMWT was replaced in 2002 with the more effective Spring Kodiak Trawl (SKT). All fish, shrimp, and jellyfish are identified and enumerated. In addition, the crew measures water temperature (°C), specific conductance (µs/cm), Secchi depth, and Turbidity (NTU).

FMWT also currently collects meso- (copepods and cladocerans) and macro- (mysids and amphipods) zooplankton samples at 35 stations. Midwater and zooplankton tows conducted by FMWT allow for determination of available zooplankton prey resources. FMWT equipment and methods have remained consistent since the survey's inception, which allows annual abundance indices to be compared across time.

Monthly and annual abundance indices are calculated using catch data from 100 “index” stations grouped into 14 regional “areas”. Monthly indices are calculated by averaging catch per tow for index stations in each regional area, multiplying these means by their respective weighting factors (i.e., a scalar based on water volume) for each area and summing these products for all 14 areas. Annual abundance indices are the sum of the 4 (September-December) monthly indices.

The FMWT catch data has been used to meet permit obligations to the State Water Resources Control Board (SW and DRCB) via Water Rights Decisions (D-1485 and D-1641) and USFWS-NMFS biological opinions for Delta Smelt (Hypomesus transpacificus), and for incidental take permits issued by CDFW for operation of Central Valley Project (CVP) and State Water Project (SWP). For more FMWT information, as well as a user copy of our Microsoft Access, please visit our website: wildlife.ca.gov/Conservation/Delta/Fall-Midwater-Trawl ## About This Federated Record This CNRA Open Data Platform record is based on metadata federated from the Environmental Data Initiative (EDI) Data Portal.

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