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SI curves for spawning (Fig. 4) were taken from the HSI model section (V6, V" Ve, V12). Assumptions and sources used in developing the curves are in Table 1. e Egg incubation. For IFIM analyses of white sucker egg incubation habitat, use curves for the time period from the beginning of spawning to 14 days beyond the end of spawning. All SI curves for egg incubation (Fig. 5) were taken from the HSI model section (V" Va, V12) except for the temperature curve, which was taken from McCormick et al. (1977). See Table 1 for assump- tions and information sources. Fry. For I FIM ana lyses of white sucker fry habi tat, curves shoul d be used for the time period beginning with the end of spawning, and ending approx- imately 2 months after spawning, at which time fry become juveniles (at lengths of 0.7 to 0.9 inches, when their mouths become ventral). Very little informa- tion was found concerning fry habitat requirements. The SI curve for fry depth (Fig. 6) was derived from observations of fry inhabiting the upper 6 inches of the water column (Stewart 1926), and the assumption that a maximum depth does not ex i st. The SI curve for fry ve 1 ocity was based entirely on professional guesswork, and the assumption that free-swimming fry can tolerate only the lowest of velocities because of their small size. The SI curve for fry substrate resulted from the assumption that substrate type is unimportant to fry after their emergence from the gravel. The SI curve for fry cover was taken from the HSI model section (Vg), and the assumption that the cover requirements for fry are the same as for juveniles and adults. The SI curve for fry temperature was taken from McCormick et al. (1977). e Juvenile. For IFIM analyses of white sucker juvenile habitat, curves should be used for individuals 1.0 to 9.9 inches in length, or from age two months to age at sexual maturity (usually ages III to VIII; Carlander 1969). SI curves were taken from the HSI model section (V4, Vg, V1], V16), except for the substrate curve. Juveni 1 es and adul ts have been observed over all forms of substrate ranging from sludge to rock (Thompson and Hunt 1930; Shurrager 1932). See Table 1 for all other assumptions and information sources. Adult. For IFIM analyses of white sucker adult habitat, all curves are the same as for juveniles, and assumptions are outlined in Table 1. Adults are considered to be sexually mature at lengths ~ 10 inches. REFERENCES Aggus, L. R., and D. 1. Morais. 1979. Habitat suitability index equations for reservoi rs based on standi ng crop of fi sh. Nat 1. Reservoi r Res. Prog. Unpubl. Rept. to U.S. Fish Wildl. Serv., Habitat Eval. Proc. Group, Ft. Collins, CO. 120 pp. Beamish, R. J. 1972. Lethal pH for the white suckers, Catostomus commersonii (Lacepede). Trans. Am. Fish. Soc. 101(2):355-358. 52 e