An ecological study of the minnows of the Des Moines River, Boone County, Iowa.

摘要

There are 52 species of fishes known to occur in the Des Moines River, Boone County, Iowa. The southern channel catfish and carp are the only abundant food fishes in the river.; The number of species of minnows was found to increase in Boone County with increased stream width. The hardiness of a species to withstand low oxygen and limited space is considered as an important factor in limiting the number of species in small streams subject to partial drying. Intolerance to other species is believed to be an important factor in the local abundance of the fathead minnow. Some species tend to have a limited distribution because of ecological preference. In the river, habitat preference varied among some species with light intensity and season. The speckled dace remained in the channel regardless of light and season.; Severe interspecific competition for food was not thought to exist among the minnows during the course of this investigation. Some competition possibly existed in the winter of 1946--47 for dipterous larvae; however, it appears that other compensating foods and diversified feeding habits of the minnows reduced the competition to a minimum.; The scarcity of entomostraca during late spring and early summer is believed to be a limiting factor to some fishes, including the yellow pikeperch, golden shiner, and common emerald shiner.; The abundant species of minnows in the Des Moines River are late spawners, which is correlated with low-river stage. The river shiner appears to be a late spawner and no explanation of its scarcity is given.; The total minnow population of the Des Moines River is known to be composed of 22 species. These species vary in their abundance from rare to the most abundant fishes in the river. This population is dynamic and is subjected in varying amounts to the decimating factors, depending upon the individual species' requirements. Several consecutive years of low-river stages in the spring and early summer followed by high-river stages later in the summer could have a serious effect on the present abundant species and would tend to favor greater production of the early spawners. Based on a 15-year average of river stages, there seems to be little possibility of such a condition continuing over a long period and the return of river stages to the average would again favor the now abundant species. The total population of the minnows in the Des Moines River could remain somewhat constant with great changes in the abundance of its composite species.