Factors Influencing Fish Food and Fish Production in Southwestern Streams

For the past two years surveys have been in progress on the mountain streams of the Southwest. These investigations included chemical analyses, quantitative counts of bottom food organisms, a study of the physical character of the streams, and studies of the fish such as species present, relative abundance, age, and growth rate. An intensive creel census has been undertaken in several streams. An intensive study is being made on two experimental streams, one of which has been improved to the practical limit and the other left in its original condition. The surveys have shown that vegetative cover on the watershed and especially in the canyon bottoms is of great importance in maintaining productivity. Vegetative cover is essential for retaining moisture and preventing severe floods which have been found to be the outstanding limiting factor in southwestern streams. Floods not only roll and grind the bottom materials and widen the stream bed, destroying pools and cover, but they also sweep away rich organic materials essential for an abundant bottom fauna and deposit light‐colored inorganic silt which is almost barren of life. It has been found that streams not subject to severe floods for some years are much richer than those streams having frequent floods. Studies made on the experimental streams clearly demonstrated this fact. These two streams–Upper Tonto Creek and Horton Creek–are similar in character and water supply. The unimproved stream, Tonto Creek, is, however, 0.2 mile longer and has a larger flow. Formerly it was considered the better fishing stream. Since improvement, however, an intensive creel census and food studies have shown that the improved stream, Horton Creek, is now the better stream. Last year it was found from food studies made at different times throughout the year that Horton Creek had an estimated yield of over 300 pounds more food than Tonto Creek. Also, the creel census revealed that Horton Creek yielded a greater number of fish. In addition, the catch per hour was greater on Horton Creek and the average total number of fish for each fisherman was greater. Scale studies reveal that prior to improvement the growth rate of the fish was more rapid in Tonto Creek, but since improvement it is more rapid in Horton Creek. On the average these two streams yielded about 50 pounds of trout to the acre of stream. At the market price for trout this is a return of $30.00 an acre for meat alone, not taking into consideration the recreational value. This return is very good as compared to any southwestern land and gives a more definite idea of the real value of the fish resources of the Southwest.