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than rainbow trout which helps the brown trout population maintain a more stable density in streams with light or moderate fishing pressure. Lastly, wild brown trout populations were present in all ten study sites while rainbow trout populations existed at only five sites and dominated at only two sites. PHABSIM calculates rainbow and brown trout W.U.A. separately. Total W.U.A.versus total trout standing stock should more accurately represent streams with both species. An attempt to estimate total W.U.A. was made by superimposing the rainbow and brown trout preference curves and developing a new curve which defined the overlap of the two trout (Fig. 5). The program was re-run, using the overlap velocity, depth and substrate curves. The resulting W.U.A. was then subtracted from the sum of the W.U.A. for rainbow and brown trout. The regressions for total W.U.A. versus total trout density and biomass were significant at the 0.05 level (Figs. 6 and 7). This regression analysis supports the contention that W.U.A. and trout standing stock are highly correlated. To complete the carrying capacity equation, a value for B/H (potential adult biomass per unit W.U.A.) must be supplied. This value canmbe obtained from a stream that is believed to be at its carrying capacity. An example is the South Platte River, Cheesman Canyon, trout population (catch and release area for R years) . By dividing total ?+1.iJ.A. }~y total. adult biomass for this area, the B/H value was found to be 8.6 g/ft (Table 2). The fact that this was the largest B/H value of the ten study sites is not surprising since this area has a large an~ stable adult trout population and no suckers (Table 1). Not many trout streams in Colorado fit this description. B/H values from streams with other biological characteristics could also be used. The Colorado River, similar t2o the South Platte at Cheesman Canyon, except with 10% suckers is 7.6 g/ft The South Fork of the Rio Grande is brown trout dominated (less than 5% rainbow trout), has few carry over adults and no suckers. This ~tream had the largest B/H value for areas with this characteristic, 6.5 g/ft Lastly, the North ForkMOf the South Platte ~ith a 50% brown trout and 50% sucker population had a B/H of 3.6g/f t m Example use of the carrying capacity equation Indications are that angling mortality has suppressed the trout popula- tion of the Deckers area on the South Platte River well below the physical carrying capacity of this stream (Nehring and Anderson 1983). From 1979 to 1982, the South Platte River in the Deckers area has had a total adult trout standing stock averaging 106 kg/1000 ft (203 kg/ha) and the range has been ' from 92 to 136 kg/1000 ft. The habitat quality appears to he midway between that of Cheesman Canyon (6J.U.A. = 37,050) and Trumbull (W.U.A. = 21,800). Using W.U.A. = 29,400 for Deckers, what would PHABSIM predict biomass of this area to be in the absence of angling mortality? C.C. = 29,400 ft2/1000 x 8.6 g/ft2 = 253 kg/1000 ft (485 kg/ha) Therefore, the habitat would probably support an adult population 238% larger 31