Status, Distribution, and Conservation of Native Freshwater Fishes of Western North America

Splittail “Delisting”: A Review of Recent Population Trends and Restoration Activities

Ted R. Sommer, Randall D. Baxter, and Fredrick Feyrer

doi: https://doi.org/10.47886/9781888569896.ch3

ABSTRACT Splittail Pogonichthys macrolepidotus, a minnow native to the San Francisco Estuary, was originally listed by the U.S. Fish and Wildlife Service as threatened in 1999. The listing was remanded in 2003 based on recent evidence about its status and efforts to restore the species. Although young-of-year production declined during a 6-year drought prior to the listing, the return of wet conditions in the late 1990s resulted in record indices of abundance. Much of the minnow’s historical off-channel habitat was lost by the early 1900s, but surveys suggest that the current range of splittail has stabilized. Year-class strength is directly related to the duration of inundation of remaining floodplain. Adults migrate upstream in winter or early spring to spawn on seasonally inundated vegetation. Their offspring rear in the food-rich floodplain habitat before emigrating with receding floodwaters. Based on the recognition that the species is perhaps one of the most floodplain-dependent fishes in the estuary, floodplain restoration became a central component of a major agency/stakeholder effort to fix long-standing problems in the region. Floodplain restoration is likely to substantially improve the long-term status of splittail, although extreme alterations in the food web from alien species may prevent the minnow from returning to historical levels.