important determinant of fish productivity in large river systems (Junk et al. 1989). Fish populations ultimately decrease when the amount of habitat is reduced, for example through flow reduction (Zorn et al. 2012), or infilling of aquatic habitats. The area of useable habitat varies temporally as water levels change; shoreline and littoral habitats expand and contract as water levels change, creating seasonally available habitats that are important to many species. Along with habitat quantity, the physical, chemical, and biological properties of a given habitat patch help to determine its quality and, therefore, potential productive capacity (Minns 1997; Minns et al. 2011), though what is considered ideal for one species may not be suitable for others. Both loss of habitat area and changes to habitat quality can affect the ongoing productivity
of a fishery (Randall et al. 2012). The abundance and biomass of a variety of species have been linked to numerous habitat properties beyond areal measures, including overhead and in-stream cover, flow velocity and variability, turbidity, invertebrate biomass, and aquatic vegetation (Binns and Eiserman 1979; Bowlby and Roff 1986; Hubert and Rahel 1989; Stoneman and Jones 2000; Inoue and Nakano 2001). Temperature and pH are often the most important limiting factors to the productivity of a given species, particularly over broad geographic ranges (Jowett 1992; Kwak and Waters 1997; Warren et al. 2010). Indeed, the volume of habitat with optimal thermal conditions for a given species is strongly
linked to its productivity (Christie and Regier 1988).