Delta Smelt Enclosure Studies, North Delta Arc of the upper San Francisco Estuary, CA, 2019 - 2024

This dataset comprises data from seven different enclosure studies, each of which used Delta Smelt reared by the UC Davis Fish Conservation and Culture Laboratory (FCCL). Each study had unique study questions and utilized slightly different methods. Enclosure Prototype (Rio Vista (RV) and Sacramento Deep Water Ship Channel (SDWSC)) – these studies, conducted January through February (RV) and March (SDWSC) of 2019, were designed to test different enclosure mesh sizes to assess their effects on Delta Smelt growth, survival, and feeding efficacy over a period of four weeks. Three different enclosure designs were deployed at two locations (Rio Vista and the Sacramento Deep Water Ship Channel), with 60 to 64 fish per enclosure and a control group of 30 fish at FCCL. See Baerwald et al, 2023 for details. - https://doi.org/10.1371/journal.pone.0286027 North Delta Pilot – This study, conducted in July and August of 2019, was implemented to test the feasibility of using enclosures to evaluate a flow action designed to improve food for Delta Smelt in the Yolo Bypass, and test upper thermal limits in field conditions for cultured Delta Smelt. Three enclosures were placed at Rio Vista and one enclosure was placed in the Yolo Bypass. Each enclosure held 60 fish. A control group of 90 fish was held at FCCL. The study lasted for four weeks; however, the Yolo Bypass enclosures were removed after three weeks following a heat wave that was lethal to all enclosure fish at that site. Suisun Marsh Pilot – This study, conducted in October and November of 2019, tested the feasibility of using enclosures to evaluate a flow action designed to improve low salinity habitat for Delta Smelt in Suisun Marsh. Three enclosures per site were placed at three locations (Suisun Marsh, Rio Vista, and the Yolo Bypass). Each enclosure held 60 fish, and a control group of 90 fish was held at FCCL. The study lasted for four weeks. Domestication/Behavior – This study, conducted in January and February of 2021, was designed to test the effect of domestication level on Delta Smelt survival and health in a naturalized environment. Nine enclosures, each holding 34 fish, were deployed at Rio Vista, with a control group of 40 fish held at FCCL; however, a high-wind storm event resulted in high mortality (93%) of field-deployed fish, limiting the available data from this experiment. Feeding Study – This study, conducted in February and March of 2022, was designed to test the effect of two different feeding strategies implemented at FCCL (dry-fed only, or acclimated to live-feed 30-days before the field trial) on survival, growth, and diets of fish transported to a naturalized environment. This study was designed to inform Delta Smelt supplementation strategies. Six enclosures, each holding 84 fish, were held at Rio Vista, and two control groups of 172 fish total were held at FCCL. During this study, subsamples of fish were collected and processed weekly from each enclosure and control group to provide deeper insight into fish condition and diet over time. The study ran for a total of four weeks. Biofouling Study – This study, conducted August through October of 2023, had the dual-purpose of testing: (1) Whether enclosures could be used to test the efficacy of a summer flow action to reduce salinity in Suisun Marsh and (2) Different methods for reducing biofouling on then enclosure, which in prior years had been noted as a potential confounding factor when utilizing enclosure studies during warmer months. Four enclosures were deployed at each of two locations (Rio Vista and Suisun Marsh) with each enclosure holding 70 fish. A control group of 24 fish was held at FCCL. Two of the enclosures at each field location were exchanged for clean enclosures every two weeks, while the other two enclosures at each location were scrubbed with a handheld brush once per week. The study ran for a total of six weeks. Suisun Marsh Salinity Control Gate Study – This study, conducted August and September of 2024, was designed to repeat the 2023 testing of the salinity action in Suisun Marsh to see if results were typical, though without the exchanging of enclosures. Four enclosures, each holding 70 fish, were deployed at each of two locations (Rio Vista and Suisun Marsh) for a total of four weeks. A control group of 70 fish was simultaneously held at FCCL. We had intended to run the study for six weeks; however, throughout the course of this study, the anchoring system securing the enclosures in Suisun Marsh repeatedly came loose. After the third failure, which occurred at four weeks, we made the decision to end the study.