Crisis Management: The Decline and Fall of the Fishes of the San Francisco Estuary

Like other estuaries on the Pacific Coast, the fish community of the San Francisco represents a rich and diverse combination of freshwater, marine and brackish water species.  However, heavy urbanization in the surrounding watershed, water diversions, habitat degradation, and a remarkable number of invasive species has had severe effects on many fishes.  Perhaps the best example is the recent collapse of the pelagic fish community of the upper estuary, which has become a resource issue of national significance. The consequences of the fisheries decline are most serious for delta smelt Hypomesus transpacificus, a federally listed species whose relatively narrow range overlaps with large water diversions that supply fresh water to over 23 million people and a multi-billion dollar agricultural industry. The state-listed longfin smelt Spirinchus thaleichthys shows some of the same abundance trends despite a more marine distribution.  An apex predator, the introduced striped bass Morone saxatilis has undergone a long term decline in juvenile production, while the adult population remains contrastingly strong.  One of the most striking changes has been the disappearance of another introduced species, threadfin shad Dorosoma petenense, a planktivore which for years had been one of the most abundant fishes in the freshwater portion of the estuary.