Population Structure and Viability Criteria for Interior Columbia Basin Salmon ESUs and Steelhead DPSs

NOAA Fisheries has designated four evolutionarily significant units (ESUs) and three distinct population segments (DPSs) in the Interior Columbia River basin as threatened or endangered under the Endangered Species Act.    The Interior Columbia River basin is one of four geographic regions designated as salmonid recovery planning domains in the Pacific Northwest.    NOAA Fisheries established technical recovery teams for each domain, charging them with developing viability criteria and technical assistance specifically applicable to listed ESUs/DPSs within their domains.   The Interior Columbia Technical Recovery Team (ICTRT) based viability criteria for each listed interior Columbia River salmonid ESU/DPS on previously developed viable salmonid population concepts.   Interior Columbia ESU/DPSs vary considerably in population structure, diversity and status.   The viability criteria and technical guidance developed by the ICTRT were specifically designed to inform establishing long term recovery objectives and to aid policy makers and recovery planners in targeting efforts to move towards those objectives.    

The ICTRT viability criteria at the ESU/DPS level are expressed in terms of risk ratings for component populations organized by major population groupings.   The population structure within each of the ESUs was determined based a number of factors including: genetic attributes; dispersal distances and rates, drainage structure; life history patterns and environmental characteristics.   ICTRT criteria for moderate, low and very low risk populations are expressed as a composite of several specific factors organized into two major subsets.     Abundance and productivity are evaluated relative to model generated viability curves corresponding to particular risk thresholds.   Spatial structure and diversity criteria include components that directly correspond to population characteristics (life history, phenotypic and genetic diversity) and indirect factors (hatchery spawner influences, habitat diversity, and anthropogenic selectivity).   The ICTRT developed and applied spatially explicit historical habitat potential analyses in formulating the viability criteria.

In addition to providing examples aid in applying the viability criteria, the ICTRT also developed guidance on associated topics including:  alternative recovery scenarios; assessing the potential contribution of restored natural production in extirpated populations or major population groupings to ESU/DPS viability; assessing current gaps relative to viability criteria; and opportunities to reduce significant uncertainties in assessing current status vs. viability criteria.  ICTRT viability criteria and population structure have been used in developing recovery plans, prioritizing regional research and monitoring efforts and in framing ESA level consultations on specific actions.