DOI: 10.6073/pasta/19a7dcaf26f9d6a9e79fcbdae781d05b
title: Interagency Ecological Program: Drift invertebrate and ichthyoplankton catch and water quality from the Sacramento River channel, and Sacramento River floodplain and tidal slough, collected by the Yolo Bypass Fish Monitoring Program, 1998-2022

description: Largely supported by the Interagency Ecological Program (IEP), California Department of Water Resources (DWR) has operated a fish monitoring program in the Yolo Bypass, a seasonal floodplain and tidal slough, since 1998.
 The objectives of the Yolo Bypass Fish Monitoring Program (YBFMP) are to:
 1. Collect baseline data on water quality, chlorophyll, lower trophic level biota, and fish in the Yolo Bypass to monitor spatial and temporal changes in trends and abundance.
 2. Analyze and communicate Yolo Bypass data with interested parties and the scientific and management communities to address pertinent management-related questions.
 3. Provide technical expertise on Yolo Bypass aquatic ecology and monitoring and sampling methods.
 Aquatic and terrestrial insects are an important component in the diet of juvenile and adult fishes within the San Francisco Estuary, including two important native fishes: juvenile Chinook Salmon and Sacramento Splittail. The YBFMP collects drift invertebrates year-round from two sites. Currently, samples are collected biweekly (every other week) to weekly (during floodplain inundation) using a rectangular aquatic drift net that sits at the surface of the water. Invertebrates are identified and enumerated by contractors (currently EcoAnalysts, Inc.). The goals of the monitoring program are to compare the seasonal variations in densities and species trends of aquatic and terrestrial insects/non-insects within the Sacramento River channel and the Yolo Bypass, the river’s seasonal floodplain.
 Drift invertebrate Key findings to date include: (1) Chinook Salmon sampled in the floodplain had diets comprised of 90% Dipterans and zooplankton, with Chironomidae being the dominant Diptera family (Sommer et al., 2001), (2) The floodplain of the Yolo Bypass contains significantly higher densities of Diptera (Diptera densities being positively associated with flow) and terrestrial invertebrates than the adjacent Sacramento River (Sommer et al. 2001b: Sommer et al. 2004: Sommer et al. 2007), (3) A major portion of the diet of juvenile Sacramento Splittail are chironomid larvae (Kurth and Nobriga 2001, Moyle et al. 2004, Sommer et al. 2007), and (4) The Yolo Bypass was the site of the discovery of a new aestivating and winter emerging chironomid; Hydrobaenus saetheri (Cranston et al. 2007).
 The collection of ichthyoplankton is one of multiple elements of the YBFMP. Currently, the YBFMP collects ichthyoplankton in the Yolo Bypass from January to July. Historically, ichthyoplankton were also sampled in the Sacramento River, but due to low catch, this was stopped in 2019. Sampling is conducted with a 500-micron mesh conical plankton net. Fish are identified and enumerated by contractors (currently EcoAnalysts, Inc). The initial goal of ichthyoplankton monitoring was to compare the seasonal variations in densities and species trends within the Sacramento River channel and the Yolo Bypass, the river’s seasonal floodplain (Sommer et al. 2003). The collection of ichthyoplankton samples is an important element in determining the annual presence, timing, and recruitment success of fishes utilizing the Yolo Bypass. Data on ichthyoplankton and associated water quality parameters are presented in this dataset.
 Key findings to date include: (1) 26 species of fish larvae were observed in the Yolo Bypass during the 20-years of monitoring (Mollie Ogaz and J. Frantzich, DWR, unpublished data), including Delta Smelt, Hypomesus transpacificus (Sommer et al 2004); (2) The native Prickly Sculpin and non-native Threadfin Shad dominated samples, contributing to over 60% of the total larval catch (Mollie Ogaz and J. Frantzich, DWR, unpublished data); (3) Native species made up a higher percent of total catch in the Yolo Bypass (22.43%) in comparison to in the Sacramento River (10.2%), and appeared earlier in the year than many non-natives (Mollie Ogaz and J. Frantzich, DWR, unpublished data); (4) Similar to other seasonal floodplains in the San Francisco Estuary, alien fishes made up a large portion of the assemblage of early life stages in the Yolo Bypass (Sommer et al 2004); (5) Water temperature and stage are the best explanatory
 environmental variables for larval fish abundance in the Yolo Bypass (p=0.001). Flow was not statistically significant (Mollie Ogaz and J. Frantzich, DWR, unpublished data); (6) Species richness and diversity are higher in the Yolo bypass in comparison to in the Sacramento River (Sommer et al. 2004).