Estimating the Freshwater Component of Essential Fish Habitat for Pacific Salmon with the Shiraz Model

摘要

The 1996 Sustainable Fisheries Act states that all federal fisheries management plans should contain a description of essential fish habitat (EFH). While much emphasis has been placed on estimating EFH for marine stocks, very little attention has beenpaid to doing so for Pacific salmon Oncorhynchus spp., in part due to their complex life histories. An earlier assessment of EFH for Pacific salmon across the west coast of the United States focused on the freshwater component of EFH due to limited knowledge about marine distributions. That analysis concluded that a more in-depth and smaller-scale examination was needed to assess how freshwater habitat affects the various life stages. Here we use a detailed life history model for Pacific salmon to estimate the freshwater component of EFH for two threatened populations of Chinook salmon within a large watershed draining into Puget Sound, Washington, USA. By accounting for proposed harvest rates, hatchery practices, and habitat structure, we identified23 of 50 subbasins as EFH for ensuring no significant decrease in the total number of spawners relative to current average escapement. Our analytical framework could be easily applied to other populations or species of salmon to aid in developing recovery and management plans.