Abstract
A Bayesian hierarchical model that integrated information about state and observation processes was used to estimate the number of adult Delta Smelt entrained into the southern Sacramento−San Joaquin Delta during water export operations by the California State Water Project and the Central Valley Project. The model hierarchy accounted for dynamic processes of transport, survival, sampling efficiency, and observation. Water export, mark−recapture, and fish facility count data informed each process. Model diagnostics and simulation testing indicated a good fit of the model, and that parameters were jointly estimable in the Bayesian hierarchical model framework. The model was limited, however, by sparse data to estimate survival and State Water Project sampling efficiency. Total December to March entrainment of adult Delta Smelt ranged from an estimated 142,488 fish in 2000 to 53 fish in 2014, and the efficiency of louvers used to divert entrained fish to fish facilities appeared to decline at high and low primary intake channel velocities. Though applied to Delta Smelt, the hierarchical modeling framework was sufficiently flexible to estimate the entrainment of other pelagic species.
Highlights
The process of entrainment is broadly defined as the geographic redistribution of a population via hydrodynamic advection
The abundance of fish lost to entrainment has at times been considered a threat to population viability, and many entrainment mitigation actions have occurred at the expense of water exports and foregone agricultural production (Yoon 2014)
Inclusion of σtransport in the model fit to Delta Smelt resulted in very little change between prior and posterior, indicating that transport error was not informed by the model or available Delta Smelt data. σtransport was dropped from the Delta Smelt model, and Equation 1 was modified to logit(ptransport,m,y) = α1 ∗
Summary
The process of entrainment is broadly defined as the geographic redistribution of a population via hydrodynamic advection. Southern Sacramento− San Joaquin Delta (South Delta) (Figure 1) entrainment, or advection of fishes into the South Delta, occurs during the process of water extraction and is a primary management concern, for those species with threatened or endangered status (USFWS 2008; NMFS 2009). The abundance of fish lost to entrainment has at times been considered a threat to population viability, and many entrainment mitigation actions have occurred at the expense of water exports and foregone agricultural production (Yoon 2014). Assessing the risk imposed by entrainment on population viability depends on the number entrained, the size of the population, SAN FRANCISCO ESTUARY & WATERSHED SCIENCE Sacramento-San. VOLUME 17, ISSUE 4, ARTICLE 4.
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