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backwaters and gravel pits combined account for 72%. Use of runs drops off entirely during June. The spring period ends when adults return to their home range area. Summer There appears to be no clear distinction between a spring and summer period for razorback suckers. July might be viewed as a transitional month between the spring spawning period (late April through late June) and summer (August through October) use of the non-spawning home range. In July, chute-channel backwaters continue to be used (36%) but gravel pits are no longer available. Use of pools and slow runs begins to increase again in July. July, along with the spring months of May and June is the only period that razorback sucker are sometimes found inhabiting shoreline habitat (7-9%). During the August-October period, habitat usage is fairly evenly divided between pools and slow runs which together are used almost exclusively. Seasonal Partitioning of the Year Though coexisting under the same conditions, the different behavioral patterns of razorback sucker and Colorado squawfish result in a year that is partitioned somewhat differently. However, because we can only recommend one flow regime for the river, a third seasonal partitioning was made that was a composite of the ones made for each species. Summer and winter flow needs of razorback sucker in the 15-mile reach could not be addressed in this report because of a lack of 15- mile reach summer and winter habitat use data, i.e., radio-tagged razorback suckers spent their summers and winters in the adjacent 18-mile reach. However, to keep things consistent, we used patterns of habitat use of both species to partition seasons in a way that can be used for both reaches. Transitional periods were either lumped or split but the core months of each season stayed basically the same (Fig. 7). A distinct winter period emerged in which averaged pool use was greater than 40% for all months and use of slow runs was 20-40%. Winter included November, December, January, February and March. A spring season included April, May and June when use of pools averaged 30-40% and backwater use was 20-40%. Summer included August, September and October. In October, the diversity of habitats used declines and pool use increases for both species. However, slow run use is still high and pool use is not nearly as high as during winter. Also, main channel temperatures are still high enough for the fish to be quite active. July appears to be more of a transition month. Although habitat use for Colorado squawfish is fairly constant during July, August and September, habitat use by razorback sucker in July is more similar to that during May and June, particularly the continued high use of backwaters (36%). Besides lumping March in with the winter months, the biggest departure in seasonal partitioning from the earlier flow recommendations is including October in the summer period and splitting out July from the summer and including it as part of spring. Including July as one of the spring months also makes sense from a hydrologic standpoint; flow levels are still quite high, considerably above base flow. Thus, we end up with a spring period which includes the runoff months and two base- flow periods, summer and winter. 20