Delta Smelt stress responses during fish salvage at the John E. Skinner Delta Fish Protective Facility, California

The John E. Skinner Delta Fish Protective Facility (Skinner Fish Facility) diverts entrained fish from the State Water Project’s pumping facilities in the southern Sacramento-San Joaquin Delta (the Delta) and transports them via tanker trucks away from the immediate influence of the export pumps. During this process, the fish are counted and released back into the Delta, generally known as fish salvage. Since fish are caught and released back into the Delta, this whole process involves various points that can be stressful to fish, such as the Delta Smelt (Hypomesus transpacificus), a state and federally listed species. To understand this process and improve fish facilities function, an investigation was conducted in 2005–2006, in which we evaluated sublethal stress associated with the terminal portion of the fish salvage process. This study included fish collection, handling, transportation, and release (CHTR) away from the export facilities. Physiological stress parameters for Delta Smelt were measured in the Skinner Fish Facility. We inserted wild and cultured adult Delta Smelt into the CHTR process and later sampled for plasma cortisol, glucose, and lactate, which typically respond to acute and cumulative stress in fish. To help identify the source of overall stress response, we partitioned CHTR into three test phases: collection and handling, trucking and release, and uninterrupted CHTR. Differences in the delayed stress response between the different phases of CHTR were evaluated. Delta Smelt experienced stress in all phases of the CHTR process and in experimental handling controls indicated by higher plasma cortisol concentrations compared to their pre-experiment levels. Wild Delta Smelt experienced higher levels of cortisol response and took longer to recover than did cultured Delta Smelt.