Stability of a Stream Fish Population

Abstract

The study of fish populations in streams requires that definite information be known about the movement of fish, since the latter is not confined as it is in lakes or ponds. If fish move long distances, long distances in streams will have to be studied in order to include a "natural" population; if fish do not move very much the technical problems are simplified greatly. Fish of 9 spp. in a small creek in s. Indiana were caught by the electric fish shocker and marked by fin-clipping so that fish from adjoining sections could be identified. The area was subdivided into 5 sections. The whole area was 0.25 mile long, was about 30 ft. wide and had a max. depth of 3 ft. A period of 42 days elapsed between the time the fish were marked and the time some of them were recaptured. It was discovered that 75% of all individuals of the 9 spp. marked were found in their original location. Two weeks later a spot check showed 70% living in the same place where they were 1st marked. Longear sunfish, rock bass, and green sunfish definitely seemed to have "homes" during the summer, but none of the spp. strayed great distances. Small longear sunfish displayed the same tendency to remain "home" as large longears. The evidence that these fish do have homes is strengthened by the fact that a flash flood occurred between the time of marking and the time of recapture which subjected the population to a natural physical stress. The movement which did take place was generally upstream.