Southern Steelhead: Ecology, Evolution, and Complexity

In 1997 the National Marine Fisheries Services (NMFS) listed two distinct populations segments (DPSs) of steelhead (Oncorhynchus mykiss) within the southern half of coastal California at the southern extent of their range in North America: a threatened set of sub-populations along the south-central coast and an endangered set of sub-populations along the south coast; the range of the set of southern sub-populations was extended to the U.S. - Mexico border in 2002.

NMFS Technical Recovery Team (TRT) for southern steelhead has divided the South-Central and Southern California Coast Steelhead DPSs into nine Biogeographic Population Groups (BPGs), characterized by a distinguishing suite of physical, climatic and hydrologic features.  Recovery of the southern steelhead DPSs will require the restoration of a minimum number of populations within each of the nine BPGs.  The core watersheds identified in this biological recovery strategy are geographically dispersed across the recovery planning area (extending from Monterey Bay to the U.S. - Mexico Boarder) to preserve the existing diversity of life-history forms (ranging from anadromous to resident) and their evolutionary trajectories.  Additionally this biological recovery strategy is intended to minimize the likelihood of extirpation of individual populations within each BPG by natural perturbations (ranging from periodic droughts and wildfires to longer range climatic changes), and to preserve the potential natural dispersal of fishes between watersheds.

The Recovery Plans for the southern steelhead DPSs identify a series of recovery actions intended to address the threats currently facing the species, as well as future threats posed by climate changes, and related habitat transformations.   Additionally, a long-term research and monitoring program is proposed to address a number of key issues (such as the relationship between anadromous and resident forms) and refine the population and DPS-wide viability criteria developed by the TRT.  Recovery will require re-integrating the listed populations back into habitats in a manner which allows for the co-occupancy of watersheds populated with approximately 27 million people.