Entrainment at the South Delta pumps of the State Water Project and the Central Valley Project has been a concern for years, but disentangling its impact on the dwindling smelt population from those of other environmental and water management factors isn’t easy, and operational differences between the SWP and CVP facilities complicate analysis. Now, US Fish and Wildlife Service statistician Will Smith has developed computer models for entrainment effects on different smelt life stages, part of a larger Delta Smelt Life Cycle project being rolled out this month; his model of adult smelt entrainment was published in the December issue of San Francisco Estuary and Watershed Science (a separate model for postlarval smelt will appear in another journal). “Adults exhibit behavior that changes under different environmental conditions,” says Smith. The adult model builds on San Francisco State University biologist Wim Kimmerer’s 2008 prototype, and differs from it in being dynamic (allowing for variations in channel velocity, for example) and hierarchical (with parameters like sampling, survival, and transport nested like Russian dolls.) It’s open to revision if new research sheds light on adult behavior. Delta smelt abundance estimates based on field surveys declined by 98 percent between 1995 and 2015; Smith hopes his work and the overall Life Cycle Project will allow more accurate estimation of the fish’s true state of abundance and retrospective assessment of the effectiveness of conservation measures. “The critical issue,” he says, “is that the declining number of fish entrained could be due either to management or to the declining abundance in the population, or to both.”

 

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Researchers hope new computer models will help clarify the effects of entrainment on the population of endangered Delta smelt.

Entrainment at the South Delta pumps of the State Water Project and the Central Valley Project has been a concern for years, but disentangling its impact on the dwindling smelt population from those of other environmental and water management factors isn’t easy, and operational differences between the SWP and CVP facilities complicate analysis. Now, US Fish and Wildlife Service statistician Will Smith has developed computer models for entrainment effects on different smelt life stages, part of a larger Delta Smelt Life Cycle project being rolled out this month; his model of adult smelt entrainment was published in the December issue of San Francisco Estuary and Watershed Science (a separate model for postlarval smelt will appear in another journal). “Adults exhibit behavior that changes under different environmental conditions," says Smith. The adult model builds on San Francisco State University biologist Wim Kimmerer’s 2008 prototype, and differs from it in being dynamic (allowing for variations in channel velocity, for example) and hierarchical (with parameters like sampling, survival, and transport nested like Russian dolls.) It’s open to revision if new research sheds light on adult behavior. Delta smelt abundance estimates based on field surveys declined by 98 percent between 1995 and 2015; Smith hopes his work and the overall Life Cycle Project will allow more accurate estimation of the fish’s true state of abundance and retrospective assessment of the effectiveness of conservation measures. “The critical issue,” he says, “is that the declining number of fish entrained could be due either to management or to the declining abundance in the population, or to both.”