Here we describe one conservation tool that will help to identify particularly significant river basins of the North Pacific for the conservation of salmon: the first Pacific-Rim wide assessment of salmon populations at a consistent scale.
In conjunction with a scientific advisory panel and a peer review workshop we developed four criteria for the Pacific Salmon Conservation Assessment (PSCA) to provide an indication of aquatic ecosystem and salmon population resilience at the basin scale. These criteria are salmon abundance, diversity, hatchery influence, and landscape suitability.
Highly abundant salmon populations have more “cushion” with which to absorb anthropogenic or natural disturbance (Quigley and Arbelbide 1997; McElhany et al. 2000). They may also produce more strays to supplement or repopulate nearby rivers, thereby contributing to recovery in impacted landscapes (Cooper & Mangel 1999; Levin & Schiewe 2001).
Second, populations with high species and life history diversity spread risk and the effects of disturbance across multiple life history strategies that may respond differentially to threats and stresses (Hilborn et al. 2003). Diversity also provides the reserves from which advantageous adaptations to future climate and other stresses may emerge.
As this assessment focuses on wild salmon, hatchery influence on wild populations is treated as a negative factor due to the potential for genetic disruption, overharvest of mixed stocks, and competitive effects on or displacement of wild fish (NRC 1996; Williams 2005). While hatchery reform programs are currently underway to mitigate impacts, historical impacts have been predominately negative.
Rivers with intact ecosystem processes are more likely to contain the intact ecosystem processes that supply wood, nutrients, and sediment, regulate hydrology and temperature, and provide connectivity and other aquatic ecosystem processes necessary to aquatic life. These rivers are also more likely to contain the disturbance regimes and diversity of microhabitats necessary to produce abundant salmon and to support resilient biological diversity (Williams 2005; Stanford et al. 2005; Stanford and Ward 1993; Ward et al. 2002).
