UC Davis Suisun Marsh Fish Study, CA,1980-2024

Suisun Marsh, at the geographic center of the northern San Francisco Estuary, provides important habitat for native and non-native fishes, as well as many valued and endangered plants, reptiles, mammals, and birds. The University of California, Davis, Suisun Marsh Fish Study, in partnership with the California Department of Water Resources (DWR), has systematically monitored the marsh's fish populations since January 1980 (O'Rear et al. 2023). The study’s main purpose has been to determine natural and human-caused factors affecting fish and invertebrate distribution and abundance.
All sampling has occurred in Suisun Marsh, mostly in subtidal sloughs. Sampling began in 1979, but standardized methods and stations were not implemented until 1980. Sampling has occurred monthly from January 1980 to the present at geographically fixed stations. Fixed stations have been necessary because snags preclude uninterrupted trawls in many sections of smaller sloughs. Originally, 48 stations were selected haphazardly that could be easily and safely sampled by boat and covered the breadth of Suisun Marsh to ensure capture of all variability in fish populations. However, the emphasis has been on sampling smaller sloughs because they exhibit greater variability in a smaller space than the marsh's two big sloughs (Suisun and Montezuma), and because only the big sloughs are sampled by other long-term monitoring projects such as California Fish and Wildlife's Fall Midwater Trawl. The 48 stations were sampled in 1980 and 1981. Water quality and catches were then compared across these stations to locate redundancies and thereby improve logistical efficiency while maximizing capture of variation by eliminating uninformative stations (Brown et al. 1981). Seventeen stations were then chosen and were continuously sampled from 1980 through 1993. Geographic scope was reassessed in 1994, when sampling was reinitiated in the northeast marsh in Denverton and Nurse sloughs at four stations (DV2, DV3, NS2, NS3; Figure B), in part to look for dwindling fish species [e.g., delta smelt (Hypomesus transpacificus), Sacramento splittail (Pogonichthys macrolepidotus)]. Catches in Nurse and Denverton sloughs were found to be unique (Matern et al. 2002); thereafter, those four stations have been included in the regular sampling, with a total of 21 stations. In 2014, to complement continuous water-quality sampling from the salinity control gates to the very top of Denverton Slough (Montgomery et al. 2016), three more stations as part of the UC Davis Arc Project were added to the 21 stations, resulting in 24 stations that are currently sampled monthly. These three additional stations (DV1, NS1, and MZ6) have also been retained because (1) they better captured gradients in water-quality conditions less discernable with the four stations (Montgomery et al. 2015), and (2) they surround areas slated for tidal restoration, increasing baseline information needed to assess restoration actions. Additionally, the transect from the MZ1 station in Montezuma Slough to the DV1 station also allows assessment of the extent of the impact of the salinity control gates (Beakes et al. 2020) in the most valuable area of the marsh for fishes (Moyle et al. 2014). Many other stations were sampled intermittently for small ancillary projects to the Suisun Marsh Fish Study.
Two dedicated people - the Principal Investigator and the Supervisor - have been the primary ones paid on the study, with crews filled out with part-time staff and/or volunteers, generally graduate students but also undergraduate students, agency employees, or any other person interested in Suisun Marsh. Most supervisors have been graduate students of Peter Moyle. Most crews have consisted of three people, often four, and sometimes only two if both people are well-versed in all aspects of the sampling.
Literature Cited
Beakes, Michael P., Cory Graham, J. Louise Conrad, James R. White, Michael Koohafkan, John Durand, and Ted Sommer. 2020. Large-Scale Flow Management Action Drives Estuarine Ecological Response. North American Journal of Fisheries Management. https://doi.org/10.1002/nafm.10529.
Brown, L., R. A. Daniels, B. Herbold, and P. B. Moyle. 1981. A Survey of the Fishes of Suisun Marsh: Progress Report submitted to DWR. 23 pp.
Matern, Scott A., Peter B. Moyle, and Leslie C. Pierce. 2002. Native and Alien Fishes in a California Estuarine Marsh: Twenty-One Years of Changing Assemblages. Transactions of the American Fisheries Society 131 (5): 797–816. https://doi.org/10.1577/1548-8659(2002)131<0797:NAAFIA>2.0.CO;2.
Montgomery, Jacob, John R. Durand, and Peter Moyle. 2016. Zooplankton Biomass and Chlorophyll-a Trends in the North Delta Arc: Two Consecutive Drought Years. IEP Newsletter 28 (3): 14–23.
Moyle, Peter B., Amber D. Manfree, and Peggy L. Fiedler. 2014. Suisun Marsh: Ecological History and Possible Futures. Univ of California Press.
O’Rear, Teejay A, Peter B Moyle, and John R Durand. 2023. Trends in Fish and Invertebrate Populations of Suisun Marsh January 2022 - December 2022. Report to DWR.