11 CHAPTER Modeling Anadromous Salmonid Life-history Marc Mangel 1, * and William H. Satterthwaite 2 Introduction Modeling anadromous salmonid life history could be an entire book itself, so in this chapter we are selective in both the literature that we cite and the methods we review. In particular, although we give an overview of the main methods that could be used to model anadromous life histories, we focus on state dependent life history theory implemented by Stochastic Dynamic Programming (SDP) (Mangel and Clark 1988; Mangel and Ludwig 1992; Houston and McNamara 1999; Clark and Mangel 2000) to capture the dependence of patterns of development and behavior on physiological state. That is, in order to understand anadromy, particularly in changing environments, we need to understand how natural selection acts on development and behavior in the context of trade-offs and fitness. Natural and sexual selection act to optimize from available variants, which are products of previous optimization events. Thus, state dependent life history theory, implemented by SDP is a powerful tool allowing us to formally analyze the outcomes of living systems at any point in evolutionary history. The approaches we describe here were first developed by one of us (Mangel) over about a decade long period in collaboration with Felicity Huntingford, Neil Metcalfe, and John Thorpe with Atlantic salmon Salmo salar in Scotland in our minds. They 1 Center for Stock Assessment Research, University of California, Santa Cruz, CA, and; Department of Biology, University of Bergen, Bergen, Norway, 1-831-234-2970. E-mail: msmangel@ucsc.edu 2 Southwest Fisheries Science Center, NOAA Fisheries, 110 Shaffer Rd, Santa Cruz, CA 95060, and; Center for Stock Assessment Research, University of California, Santa Cruz, CA, 1-831-420-3997. E-mail: will.satterthwaite@noaa.gov * Corresponding author © 2016 by Taylor & Francis Group, LLC