Production of Mountain Whitefish (Prosopium williamsoni) in Altered and Unaltered Reaches of Two Intermountain Streams in Their Alluvial Flood Plains

• Main Author: Ottenbacher, Michael J.
• Format: Others
• Published: DigitalCommons@USU 1980
• Subjects: mountain whitefish; altered reach; unaltered reach; intermountain stream; alluvial flood plains; Aquaculture and Fisheries; Ecology and Evolutionary Biology; Environmental Sciences
• Online Access: https://digitalcommons.usu.edu/etd/6367; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=7435&context=etd

Estimates of production and related parameters (growth rate, density, standing crop) were made for populations of mountain whitefish in altered and "unaltered" areas of the Glacksmith Fork and Logan River, UtJh from spring 1975 through summer 1976. Capture records of marked whitefish were also analyzed to describe fish movement and check on assumptions implicit in the population estimator. Mean weights and instantaneous growth rates of whitefish were similar at all sites for comparable size/age groups. Among sites, differences in production per sampling interval and annual production were due mainly to differences in standing crop and/or age structure. Estimates of mountain whitefish density varied by site and season and ranged from 0 to 3,467 fish/ha, with the highest densities occurring during the fall and winter (spawning season) and the lowest during the summer when streamflows were low. Estimates of standing crops of whitefish followed a pattern similar to density. In the sites where fish remained during the summer most production occurred during the spring and summer. A bulldozed reach of the Logan River (including an "unstable" section) had the highest annual production of mountain whitefish (51.85 kg/ha/yr)--almost double the annual production for the same reach when the unstable section was not included (31.85 kg/ha/yr). The highest annual production of whitefish in sites in the Blacksmith Fork River (51.23 kg/ha/yr) occurred in a reach that had been recently dredged but still contained a riffle and pool structure. Annual production of whitefish was low in a recently bulldozed reach (5.47 kg/ha/yr) and an old bulldozed reach (10.08 kg/ha/yr) of the Blacksmith Fork River where suitable habitat (pools and glides) was lacking, especially during the summer months. Mountain whitefish remained or returned to reaches after channel alterations as long as water depth remained sufficient. This study illustrated the necessity of frequent sampling when attempting to evaluate the effects of perturbations on fish populations or in production studies in general.