Abstract
Hydrodynamic models have been used to estimate rates of ichthyoplankton transport across marine and estuarine environments and subsequent geographic isolation of a portion of the population (i.e., entrainment). Combining simulated data from hydrodynamic models with data from fish populations can provide more information, including estimates of regional abundance. Entrainment of postlarval delta smelt (Hypomesus transpacificus), a threatened species endemic to California’s Sacramento–San Joaquin Delta, caused by water export operations, was modeled using a Bayesian hierarchical model. The model was fit using data spanning years 1995–2015 from multiple sources: hydrodynamic particle tracking, fish length composition, mark–recapture, and count data from entrainment monitoring. Estimates of the entrainment of postlarval delta smelt ranged from 10 (SD = 23) in May 2006 to 561 791 (SD = 246 423) in May 2002. A simulation study indicated that all model parameters were estimable, but errors in transport data led to biased estimates of entrainment. Using only single data sources rather than integration through hierarchical modeling would have underestimated uncertainty in entrainment estimates or resulted in bias if transport, survival, or sampling efficiency were unaccounted for.
Highlights
Water regulation and withdrawals contribute to habitat and population fragmentation and degradation (Dynesius and Nilsson 1994; Aparicio and others 2000) and affect multiple trophic levels (Arthur and others 1996; Jassby and others 2002; Kennish 2002; Moyle and Williams 1990; Gumpinger and Scheder 2008)
We investigated two key sources of entrainment losses of delta smelt at the State Water Project (SWP): fish facility efficiency and pre-screen losses in Clifton Court Forebay (CCF), as defined earlier
The objectives of this study were to obtain mark– recapture estimates for the: (1) fish facility efficiency for juvenile and adult delta smelt at the Skinner Delta Fish Protective Facility (SFF), (2) percent of marked juvenile and adult delta smelt released in CCF and recaptured at the SFF, and (3) pre-screen loss for juvenile and adult delta smelt
Summary
Water regulation and withdrawals contribute to habitat and population fragmentation and degradation (Dynesius and Nilsson 1994; Aparicio and others 2000) and affect multiple trophic levels (Arthur and others 1996; Jassby and others 2002; Kennish 2002; Moyle and Williams 1990; Gumpinger and Scheder 2008). Because of record low fish population abundance indices for several pelagic species since the early 2000s (Feyrer and others 2007; Sommer and others 2007; Messineo and others 2010), water allocation has become increasingly critical for the Delta of the upper San Francisco Estuary (hereafter the Delta), one of the most intensively watermanaged estuarine systems in the world. The water diversions by the State Water Project (SWP) and Central Valley Project (CVP), including water export from the south Delta for agricultural, industrial, and urban use, have long been considered factors that contribute to the decline of fishes in the upper San Francisco Estuary (Erkkila and others 1950; Stevens and Miller 1983; Moyle and others 1992; Arthur and others 1996; Bennett and Moyle 1996; Sommer and others 2007; Grimaldo and others 2009). Delta smelt was deemed to warrant federal endangered status in 2010, but was precluded from a status change because of other listing priorities (Federal Register 2010)
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