Diversity in Estuarine Habitat Utilization by Puget Sound Salmon Juveniles: Variability within and Between Species, Populations and River Systems

One of the most striking features of anadromous Pacific salmon is the wide variability in life history traits they exhibit.  Life history diversity is generally regarded as one of the ways for salmon to be resilient and persist in the face of anthropogenic and natural disturbances.  Here, I use existing data sources, including empirical studies of estuarine habitat use, otolith and scale pattern analyses, and migrant trapping data, to identify the suite of estuarine life history types of coho salmon, Chinook salmon and chum salmon that occur in a variety of different Puget Sound watersheds.  My objectives were to determine: 1) how pervasive certain life history types are in Puget Sound watersheds, 2) differences and similarities in diversity between species, and 3) some of the biological and physical characteristics of watersheds that may help explain differences and similarities in diversity (such as variability in populations sizes, watershed area, characteristics of estuarine wetlands).  Life history types were defined based upon time and size of estuarine entry, duration of estuarine residence, and patterns of estuarine habitat use.  I focused on estuaries because recent evidence suggests that estuarine habitat characteristics and the period of estuarine residence are critical to the viability of some salmon populations and can directly affect population productivity.  Further, estuaries have been the focus of considerable anthropogenic change in Puget Sound and are thus now the focus of major conservation efforts.  Restoring the breadth and diversity of juvenile life history types associated with esturies has the potential to improve salmon population viability and resilience.  An increased understanding of the relationships between the quantity and quality of different estuarine habitat types and their support of diverse life history types can help improve restoration efforts in estuaries.