Population estimates of young Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., by electrofishing in two small streams in north Norway
Heggberget, TG.; Hesthagen, T.
Institute of Freshwater Research Drottningholm Report 58: 27-33
Mark-recapture and successive-removal methods using electrofishing were analyzed at the same sampling stations in 2 small streams near Tromso, northern Norway. The mark-recapture estimates were conducted by using the Petersen and Schnabel methods, while the removal-method estimates were obtained by Zippin's method and regression analyses performed by least squares. The catch-recapture method gave fairly good estimates, while the removal methods underestimated the population size by about 50%. One of the main reasons for the underestimation by removal methods in fenced areas in small rivers is thought to be the reduced catchability of fish that have already previously experienced electric current. Because of lower efficiency for salmon, the removal methods tended to underestimate the population size to a greater degree than for trout.