The estimate of fish density and biomass in rivers on the basis of relationships between specimen size and efficiency of electrofishing

Abstract

It is shown that the catch-effort electrofifhing methods, which are those most often employed for estimates of riverine fish density and biomass, are often not precise. These multiple sampling procedures are time- and manpower-consuming, and can change the habitat and fish community structure. The results, collected in rivers of different size and character, show curvilinear relationships between the average specimen size and the percentage, number and biomass of fish caught by one electrofishing. Using such relationships minimizes the alteration of fish community structure by the sampling procedure. Conditions which must be fulfilled for proper use of the proposed relationships are discussed.