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velocity and depth. Riffle velocity (V7) and depth (VB) are important for spawning site selection. Temperature during larval development (Vs) is important to larval ontogeny and survival and to the timing of migration of larvae to a lake or riverine rearing area. The time periods specified for each variable (e.g., April through July) indicate when the variables are important for the specified life stage throughout the entire range of the species. If one of these suitability indices is used in an HSI model developed to rate habitat, the time period when the life stage is actually present, or expected to be present, should be used. , Cover. Shelter availability and presence of resting areas (V9) is assumed to enhance the carrying capacity of streams for white suckers. Percent pools (VlO) was included because pools serve as resting areas before spawning and provide cover in the form of deeper water. Model Description - Lacustrine Water quality component. Refer to riverine model description. Reproduction component. Lacustrine populations of white suckers spawn in tributary streams or in 1 ittoral areas over sand and sand/gravel substrates (VII) at suitable temperatures (V6) and dissolved oxygen levels (V3), any of which can be limiting. If stream spawning occurs, the reproduction component rating is derived from measurements taken in the riverine environment. Suitability Index (51) Graphs for Model Variables f Suitability indices for selected variables are given below. The "R" for riverine and "L" for lacustrine, under the heading "Habitat", describe where the variable should be measured. Sources of data and assumptions used to develop the suitability indices are listed in Table 1. Habitat Variable Suitability graph 10 1.0 >< 0.8 OJ "'0 s:::: ....... >, 0.6 +-' 'r- .0 0.4 <0 +-' 'r- ::l 0.2 Vl 0.0 0 100 200 300 400 JTU fJ R,L VI Maximum monthly average turbidity during the year.