Colonization Rates of Fishes in Experimentally Defaunated Warmwater Streams

The colonization of Illinois streams by fishes was measured during late spring and early summer in 18 experimentally depopulated reaches that ranged from 46 to 113 m in length. Rates of colonization in terms of total fish numbers, number of species, individual species, and community structures were measured over time intervals ranging from 0.5 to 140 h. Both the proportion of original fish abundance (all species) and the proportion of original community structure (measured by a proportional similarity index) increased with time. Linear colonization models indicated that 0.70 of the maximum proportional similarity index would be reached in 60–140 h (90% confidence limits of the model) and that 0.90 of the original fish abundance would be reached in 100–270 h. The results of this and previous studies indicate that in drainages dominated by surface runoff, disturbed fish communities in short stream reaches can quickly return to their original structures and abundances without any aid, provided that fish have unrestricted access to the reaches and that the environment returns to its original state.