Movement and Population of the Mottled Sculpin (Cottus bairdi Girard) in a Small Montana Stream

Movement and population of the mottled sculpin (Cottus bairdi Girard), excluding young-of-the-year, were studied in Trout Creek, Gallatin County, Montana between 4 August 1962 and 10 March 1963, and in the laboratory between 7 August 1962 and 21 December 1962.Fin-clipped fish were recaptured at an average rate of 23.9 per cent (38.1-11.8 per cent) for the five censuses.About 50 per cent of the recaptures were within the original section (average length 46.8 feet), and about 80 per cent were in an original section or one of the two adjacent sections (average length 153.2 feet).Upstream movement of all masked sculpins was 23.4 per cent greater than downstream movement, but downstream movement of jaw-tagged sculpins was 16.6 per cent greater than upstream.No mass upstream migration occurred.Home range was estimated to be less than 150 feet.Homing was not exhibited.About one-third of the displaced sculpins homed, one-third did not move, and one-third moved away from home.The longest upstream movement noted was 590 feet, and the longest downstream was 502 feet.Spatial isolation and aggressive behavior were not observed in a laboratory experiment, which suggests a lack of territoriality during the non-breeding season.Modified Petersen population estimates ranged from 474-555 sculpins in a 234-foot section over the five inventories, and Schumacher-Eschmeyer estimates ranged from 480-492.