Changes in Minnow Populations in a Small Desert Stream Resulting from Naturally and Artifically Induced Factors

Abstract

Population dynamics and standing crops of minnows were examined in a small Upper Sonoran stream, Arizona, between 1969 and 1971. Statistics varied from year to year, largely attributable to hardiness of the respective species, in- creased streamflow, and flooding. Consistent yearly patterns of change in length and weight and, in most cases, biomass of all three species occurred; however, condition (K) failed to display parallel trends among species. Total biomass of fishes was comprised predominantly of one cyprinid in this small stream in the arid South- west. No published data are known to me concerning fish production and/ or biomass of the few remaining low-elevation streams of the arid American Southwest. Biomass and production information are avail- able for fishes in some eastern streams, lakes, and reservoirs but are concerned with sport or commercial fisheries. This paper analyses fish population dynamics of an Arizona creek over a period of several years during cursory studies of the stream. Cave Creek, Maricopa County, Arizona, lies within the Upper So- noran life-zone approximately 50 km N of Phoenix. A general de- scription of the area is given by Stout, et al. (1970). Seven-Springs Wash, a major tributary of Cave Creek, is approximately 2 km long, extending from its confluence with Cave Creek immediately below an artificial concrete fall (1.5-2.0 m high) to its headspring. Physical and hydrological characteristics for this tributary are: mean depth, 19.6 cm; mean width, 3.32 m; total surface area, 0.55 ha; and flow rate, 0.66 m3/min. At present only a U.S. Forest Service picnic ground at the lower end of Seven-Springs Wash and a small irrigation canal diverting water from the headspring at the rate of 3.0 m3/min are ex- 1 Current address: EAFFRO, P. O. Box 1881, Kisumu, Kenya, Africa.