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Model Description - Riverine t Ri veri ne green sunfi sh habi tat is assumed to be composed of food and cover, water quality, and reproduction components. Variables that have been shown to affect growth, survival, distribution, or abundance were placed in the appropriate life requisite component (Fig. 1). Variables that did not appear to be related to a specific life requisite component were placed in the "otherll component. Information describing cause and effect relationships of variables and components in determining habitat suitability was lacking. We assumed that high values for one life requisite or variable would compensate for lower values of another life requisite, except when values for a variable approached levels that had clearly demonstrated negative impacts on growth or survival. Food and cover component. Percent bottom cover (V1) is assumed to be important because bottom cover provides habitat for aquatic insects, crayfish, and small fish which are the predominant food items of green sunfish. Bottom cover also provides resting areas with low current velocities and protection from predation. Species abundance has been positively correlated with percent cover. Percent pools (V2) is included to quantify the amount of habitat actua 1 ly used by the speci es. Food and cover have been aggregated into one component because the fish have a tendency to feed near cover. Water quality component. The water quality component is limited to dissolved oxygen (V4), turbidity (Vs), pH (V,), temperature (V7, Va), and salinity (V18) measurements. The salinity measurement is optional. These parameters have been shown to affect growth or survival. Variables related to temperature and oxygen were assumed to be limiting when they reach near-lethal levels. Toxic substances were not considered in this model. t Reproduct i on component. Temperature for spawni ng (V,) descri bes water quality conditions that affect embryonic development. Substrate (VlD) is important in determining spawning success. Current velocity (V12) within pools during spawning is important because developing eggs will not survive in areas with velocities> 15 em/sec. Other component. The variables which are in the other component also describe habitat suitability for the green sunfish, but are not specifically related to life requisite components already presented. Stream gradient (V3) is i ncl uded because green sunfi sh are most abundant in streams wi th lower gradients (~ 2 m/km). Current velocity (V11, V13) is important because green sunfish prefer low velocity areas. Stream width (V14) further describes preferred habi tat because sma 11 to medi um-si zed streams (< 30 m width) are most suitable. t 4