Population Dynamics and Evaluation of Management Scenarios for White Sturgeon in the Sacramento–San Joaquin River Basin

Abstract

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.

Habitat use differences mediate anthropogenic threat exposure in white sturgeon

“…Fish in this age range are below the slot limit, and below-slot fish, in our study, tended to be found lowest in the system, in areas tending toward higher salinity, compared with larger fish. Note that the youngest fish in our dataset was estimated at 7 years old based on the growth curve presented in Blackburn et al (2019), which Sellheim et al (2022) indicate would tend to be using higher-salinity habitats. The discrepancy in ages between these studies also highlights that telemetry data on juvenile white sturgeon are limited, resulting in uncertainty over their habitat use and movements.…”

“…For the PERMANOVA analyses, we considered three classes of fish size relative to the current slot limit on the white sturgeon recreational fishery in California, which permits only fish between 40 in (102 cm) and 60 in (152 cm) fork length to be kept. Blackburn et al (2019), analyzing fish from the same region, showed that typical white sturgeon are in the fishery from ages 10 to 15. Using growth curves from Blackburn et al (2019), we extrapolated length-at-tagging forward in time and classified fish as below slot, in the fishery, or above the slot limit at each water year.…”

“…Across the range of white sturgeon, many populations are in decline due to overfishing and habitat degradation (Hildebrand et al 2016), and the extent of state and federal protections varies among regional subpopulations (Schreier et al 2013; Hildebrand et al 2016). The Sacramento-San Joaquin population is not currently federally protected, but there is evidence that this population is in decline (Hildebrand et al 2016; Blackburn et al 2019).…”

“…Harvest rates are monitored using angler report cards and a fishery-independent stock assessment. A recent analysis estimated that the population growth rate of white sturgeon in the Sacramento and San Joaquin River systems may be below replacement levels and, consequently, the population may be in decline (Blackburn et al 2019). Moreover, despite consistent monitoring of the fishery, habitat use and movements of white sturgeon in the San Francisco Estuary and Sacramento River system are relatively little studied (but see, e.g., Johnston et al, 2020; Miller et al, 2020), leaving open questions about their ecology, patterns of habitat use, and effective approaches to improving habitat and fishing conditions to reverse declining abundance trends.…”

Estuarine Habitat Use by White Sturgeon (Acipenser transmontanus)

“…The estuary population was nearly extirpated in the late 19th century from commercial harvest, but now supports a recreational fishery (Chadwick 1959;Skinner 1962;Parks 1978;Kohlhorst 1980). However, current harvest levels are unsustainable and, together with the loss of habitat, represent a serious threat to the continued existence of the population (Blackburn et al 2019).…”