Water exports have been implicated in the decline of fish populations in the upper San Francisco Estuary, California. We evaluated the relation between delta smelt salvage at the John E. Skinner Delta Fish Protective Facility (SFF) and underlying entrainment losses at the State Water Project (SWP, south Delta). We used cultured delta smelt in mark-recapture experiments in February and March 2009 (adults) and June 2009 (juveniles) to estimate: (1) the percent of fish recaptured at the SFF of the total released at the entrance of the SFF (fish facility efficiency), (2) the percent of fish recaptured at the SFF of the total released in Clifton Court Forebay (CCF), a reservoir for SWP exports, and (3) the fish losses in CCF and before the SFF (pre-screen loss). Mean fish facility efficiency was lower in successive releases: February (53.2%), March (44.0%) and June (24.0%). The mean percent recapture of fish released at the CCF entrance was also lower over time: February (3.01%); March (0.41%) and June (0.03%). Correspondingly higher mean pre-screen losses occurred over time: February (94.3%); March (99.1%) and June (99.9%). We concluded that: (1) entrainment losses of delta smelt could be higher at times, compared to other species previously studied at the SWP; (2) pre-screen loss was the largest source of mortality for delta smelt; (3) increased release distance from the SFF and residence time in CCF-and decreased exports-resulted in a lower percentage of recaptured fish at the SFF; and (4) salvage of delta smelt at the SWP does not seem to be a consistent index of entrainment.
The Delta Smelt Hypomesus transpacificus is a protected osmerid endemic to the San Francisco estuary of California. We conducted laboratory tests on marked versus unmarked juvenile adult smelt to evaluate (1) calcein mark intensity and postmarking survival for juveniles and adults, (2) photonic mark retention and survival of adults, and (3) predation by juvenile Striped Bass Morone saxatilis. Calcein mark intensity was graded in six body sections and adults were photonically marked using four fin‐color combinations. Across all immersion times (1–7 min) all fish showed 100% mark retention 7 d after exposure to calcein concentrations of 2.5 and 5.0 g/L of water. Average survival 7 d after calcein marking was 93.9% in juveniles and 98.6% in adults. After 97 d of calcein and photonic marking, adults had weaker double marking, but each type of mark still showed 100% retention. Average survival of adult fish 70 d after marking was 98.7%. Unmarked and calcein + photonically marked adult Delta Smelt exposed to juvenile Striped Bass did not experience significantly different predation rates. Calcein is both effective and practical to batch‐mark juvenile and adult Delta Smelt. Combined calcein and photonic marking for adult Delta Smelt further enables identification of multiple groups while potentially improving mark detection in short‐term studies.Received October 1, 2012; accepted August 22, 2013Published online January 14, 2014
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