Document: MIC-3-81-14

Risk assessment for twelve salmonid evolutionarily significant units in the Columbia River basin.

MCCLURE, M.* and B.SANDERSON

National Marine Fisheries Service Seattle WA 98112 USA ¹

Abstract:
Since 1991, twelve salmonid Evolutionarily Significant Units (ESUs) in the Columbia River Basin have been listed as threatened or endangered under the Endangered Species Act. Human impacts on these stocks include in-river and ocean harvest, freshwater rearing and spawning habitat degradation and loss, estuarine habitat degradation, potential ecological and genetic interactions with hatchery fish, and the construction of dams throughout the basin. We conducted extinction risk analyses for the twelve listed ESUs, using a modified Dennis extinction analysis and a simple simulation model. In addition, we assessed the potential contribution of impacts in the "4 Hs" (habitat, harvest, hatcheries and hydropower) to current risk. Finally, we used age-structured matrix models (when possible) to identify life stages at which reductions in mortality might contribute substantially to improving population trajectories. All ESUs face substantial long-term risk; for example, the probability of extinction of Snake River stocks in the next 100 years ranges from 33-93%. Many stocks face substantial risk of extinction in the short-term as well (0-15%). Opportunities for improvements in survival vary from ESU to ESU. Some stocks may benefit significantly from actions in all areas, such as those that improve habitat, reduce harvest, and improve first year survival.

Keywords: salmon, endangered species, Columbia River, extinction risk

This abstract is being presented at: 9:00 AM in session:
Oral Session #57: Ocean-Going Fish and Mammals.