THE RELATIONSHIP BETWEEN FISH YIELD AND PRIMARY PRODUCTION IN LARGE EUROPEAN FRESH-WATER LAKES

The data published on fish yield (Yf) and primary production (PP) in t hree large European freshwater lakes (Ladoga, Ilmen and Pskovsko-Chuds koe) were analyzed on a long-term basis. The ratios between Yf and PP were found to vary from 0.02% to 0.46%. It was shown that there was an optimal level of PP, above which the efficiency of energy transfer in the pelagic food chain began to decrease. An individual optimum of PP was characteristic of each of the lakes studied. This level was prima rily determined by the original trophic status of a given lake as well as by its morphometry and hydrochemistry. The results warn practical ecologists against erroneously predicting commercial harvests from PP.