Rations and the proportions of course fish in the ration were made. Using the estimated daily rations of prey trout along with knowledge of the magnitude of the predator trout stocks, the number of prey trout by age class consumed per mile of river was calculated. The predator brown trout kill of small trout was 7, 626 fish per mile -of river in the normal angling regulation water (7. 0-inch minimum seize, any lure, -10 trout creel limit) and 3, 579 fish per mile in the special angling regulation water (9. 0-inch minimum size, flies-only, 5 trout creel limit). Kills of small brown trout were relatively low in both the normal and special regulation waters and amounted to only 217 and 218 fish per mile for the respective waters.

Brown trout are the most significant natural predator yet identified on the Au Sable in terms of total trout killed. However, because the brown trout eat only small trout they are not in direct competition with anglers, as are the American Merganser, Great Blue Heron, mink, and otter which kill more large trout.

Brown trout predation is probably detrimental to brook trout populations where brook trout fisheries are the primary management objective. However, brown trout predation is probably beneficial in controlling slow growth in high population densities of small trout. Further, if older brown trout lacked smaller trout as prey they would grow slower and fewer large "trophy" size fish would be produced. Also, the predation of the brown trout on coarse fish populations is beneficial to all trout.

Many of the trout spared from the anglers ' hooking mortality and not caught due to special regulations, are subsequently eaten by natural predators. However, in the normal regulation waters the kill of trout by natural predators is also high.