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An estimated 33 pounds/acre of brown and 60 pounds/acre of rainbow were harvested from May through August 1985 (Table 4). This represents 16% of the reduction in brown trout biomass and 105% of the reduction in rainbow biomass between April and November 1985. Discrepancies in these data, such as the large reduction in brown trout and the estimated harvest of more rainbow than were lost in the pre-to-post-fishing season population estimates, cannot be fully explained with the available information. SUMMARY AND CONCLUSIONS On Sand Creek at Ranch A, prior to the first fishing season, there was a very dense, un exploited population of wild brown trout with a carrying capacity of up to 800 pounds/acre of brown trout. The dense brown trout population showed evidence of stunting with the bulk of the fish collected ranging from six to 12 inches in length. Rainbow were incidental in numbers, but larger in average size, making up 12% of the trout numbers, but 25 % of the pre-season standing crop. Following the first season in at least 20 years, there was a reduction of 1,147 brown and 116 rainbow trout/mile between the pre- and post-fishing season population estimates. Fishing harvest, however, only accounted for 22% of this mortality in brown, but 141 % of the mortality in rainbow. Reasons for the unaccountable loss in brown trout and the harvest of more rainbow than were estimated to be lost can only be conjectured. Undoubtedly, sampling errors and variability in the estimates and techniques play an important part in these discrepancies. Actual changes in these populations, outside of the fishing mortality and expected natural mortalities, is doubtful. The difficulty in collecting fish under the assumption of equal effort in Sand Creek, combined with the sensitivity of the two-pass method to violations of this assumption, suggests that the magnitude of differences seen in these population estimates from pre- to post-fishing season may be overestimated. It appears that fishing pressure on Ranch A, although light by comparison with other streams and other portions of Sand Creek, may have had a positive effect on body condition and possibly growth through the harvest or reduction of fish over six inches. Post-season condition factors were higher in November 1985 at both stations than during either of the two pre-season sampling periods. An increase in the population of brown trout under six inches was also noted in the post-season estimate which indicates good survival and a strong year-class of 1985 young-of-the-year brown trout. Under relatively light fishing pressure, the small population of rainbow was recycled up to 1 1/2 times through catch and release fishing, while the abundant brown trout population was only slightly exploited. . Regardless of the inability to fully explain differences in the population estimates, Sand Creek remains one of the most densely populated trout streams in the state, with post-fishing season trout population estimates in excess of 500 pounds/acre. Starting in July 1986, the Wyoming Game and Fish Department will begin a 30 year lease of Ranch A for the eventual purpose of establishing a state fish hatchery and rearing station. It will be recommended that Sand Creek on Ranch A be open to fishing during the calendar year without restrictive regulations in hopes of encouraging more harvest of the over-populated brown trout. In conjunction, the trout populations will continue to be monitored for changes. Techniques will be refined to reduce sampling errors and to get more accurate estimates of all size groups. 13