Factors Affecting Fish Entrainment into Massive Water Diversions in a Tidal Freshwater Estuary: Can Fish Losses be Managed?

Abstract

Abstract.-We examined factors affecting fish entrainment at California's State Water Project and Central Valley Project, two of the largest water diversions in the world. Combined, these diversions from the upper San Francisco Estuary support a large component of the municipal and agricultural infrastructure for California. However, precipitous declines in the abundance of several estuarine fish species, notably the threatened delta smelt Hypomesus transpacificus, have generated major concern about entrainment as a possible cause of the declines. We examined a 13-year data set of export pumping operations and environmental characteristics to determine factors affecting entrainment (as indexed by salvage at fish screens) and the potential for manipulation of these factors to improve conditions for fish. Entrainment of three migratory pelagic species-delta smelt, longfin smelt Spirinchus thaleichthys, and striped bass Morone saxatilis-was primarily determined by the seasonal occurrence of particular life stages close to the export facilities. We also found that the direction and magnitude of flows through the estuary and to the export facilities were reasonable predictors of pelagic fish entrainment. Entrainment of resident demersal species (prickly sculpin Cottus asper and white catfish Ameiurus catus) and littoral species (Mississippi silverside Menidia audens and largemouth bass Micropterus salmoides) was not explained by diversion flows, although large numbers of individuals from these species were collected. Our study suggests that entrainment of pelagic species can be effectively reduced by manipulating system hydrodynamics.

Abundance Trends, Distribution, and Habitat Associations of the Invasive Mississippi Silverside (Menidia audens) in the Sacramento–San Joaquin Delta, California USA

“…It has been previously shown that estuarine species respond strongly to interannual variability in freshwater flow (Jassby et al 1995;Kimmerer 2002), though this has yet to be evaluated for Mississippi Silversides. Water diversion projects within the Delta can alter the hydrodynamics of the region and have been shown to entrain a sizeable number of Mississippi Silversides in certain years (Grimaldo et al 2009). Water temperature and turbidity may be important for Mississippi Silversides on a longer time scale based on our GAM analysis results (Question 2 above) and previous studies (Moyle 2002).…”

Forebay use and entrainment rates of resident adult fish in a large hydropower reservoir

“…However, resident species (i.e. those that do not emigrate from reservoirs) are also vulnerable to entrainment when they use habitats near water intake structures, with vulnerability to entrainment varying with factors such as species, life stage, time of day, season and operations (Coutant & Whitney 2000, Grimaldo et al 2009, Spinelli 2010.…”

Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…Once sediment enters the central Delta through the Georgiana Slough pathway, it is gradually advected southward though Old and Middle rivers into the south Delta; Wright and Morgan (2015) calculated a travel time of about 2 weeks from Freeport to the south Delta for a first flush sediment pulse in December 2012. This slow advection of sediment southward, which increases turbidity in the south Delta, has important implications because elevated turbidity in the region of the pumping facilities has been linked to high entrainment of Delta Smelt at the facilities (Grimaldo et al 2009), which can lead to curtailments of federal and state water deliveries.…”