Chinook Salmon (Oncorhynchus tshawytscha)in Puget Sound : Effects of Spatially Correlated Catastrophes on Persistence

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Abstract Recovery efforts for endangered species typically are focused at the level of the species. However, many species of conservation concern are composed of multiple populations, and these populations often exhibit a metapopulation-like structure that has a large effect on species viability (reviewed by Hanski and Gilpin 1997). Contributing to a species’ metapopulation structure is the geographic distribution of catastrophic events; such catastrophes can have a large effect on population and, therefore, species, persistence. In practice, the effects of catastrophic population loss on species viability are difficult to estimate, in part because of the dearth of information on rates and magnitudes of catastrophic events (Hanski and Gilpin 1997). Nevertheless, it is important to consider the combined effects of the spatial distribution and connectivity among populations and their likely rates of catastrophic loss and recolonization (i.e., population turnover) in estimating species persistence. Incorporating such potential effects on species viability can lead to very different strategies for recovering species (e.g., Ralls et al. 1996). In this chapter, we develop a simple model to explore the effects of both metapopulation structure and the spatial distribution of catastrophic risks on the probability of persistence of a wide-ranging species. Our focal species for the spatial model we developed is chinook salmon (Oncorhynchus tshawytscha), an anadromous fish whose geographic range extends throughout the north Pacific from Japan to southern California (Healey 1991, Myers et al. 1998). Salmonin general are characterized by a strong metapopulation-like structure because of the spatial distribution of streams they inhabit during their freshwater phase and their unique life history attributes. One of the most important of salmon life history features in their effect on population structure is their strong homing tendencies (Groot and Margolis 1991).