The Ecology and Management of Delta Smelt: Why this Annual Species May be the Most Important Non-Game Fish in the United States

While game fishes such as Chinook Salmon remain a primary focus of fisheries management along the Pacific Coast and its inland waters, the decline of an annual forage fish, Delta Smelt Hypomesus transpacificus, represents a resource issue of national significance. Along with several other pelagic fishes, this native osmerid has undergone a serious decline in the upper San Francisco estuary, leading to its listing under the federal and state endangered species acts.  Its relatively narrow range (freshwater tidal and low salinity zone) overlaps with large diversions that supply water to over 25 million people and a multi-billion dollar agricultural industry, leading to major water use conflicts.  These and related issues have stimulated fish management techniques such the control of tidal flows and turbidity levels to reduce fish losses at diversions, as well as restoration of tidal wetlands.  This rare and sensitive species is now heavily-monitored throughout the year, leading to the development of innovative new field tools such the SmeltCam, a towed video imaging system.  This information has led to substantial new insight into the biology of Delta Smelt, such as its sensitivity to invasive species, declines in the planktonic food web, and climate change.