Recent surveys suggest a declining population of White Sturgeon Acipenser transmontanus in the Sacramento–San Joaquin River basin (SSJ), California. Probable reasons for the decline include overharvest and habitat degradation compounded by poor recruitment during recent droughts. Despite the importance and status of White Sturgeon, knowledge of their population dynamics in the SSJ remains incomplete and additional information is needed to further inform management decisions. The purpose of this study was to evaluate the population dynamics of White Sturgeon in the SSJ and use the information to estimate the population‐level response under plausible management scenarios. White Sturgeon in the SSJ exhibited fast growth and high rates of mortality and experienced relatively high levels of exploitation. Under current conditions, the population will likely continue to decrease (population growth rate λ = 0.97); however, there was considerable uncertainty in estimates of future population growth. Population growth of White Sturgeon in the SSJ was most influenced by the survival of sexually mature adults. The models also suggested that White Sturgeon in the SSJ could reach the replacement rate (i.e., λ ≥ 1.00) if total annual mortality for age‐3 and older fish does not exceed 6%. Low levels of exploitation (i.e., <3%) would likely be required to maintain a stable population.
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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