Investigations on the growth and population-structure of bream (Abramis brama L.) at different areas of Lake Balaton the assessment of mortality and production

Bíró, Péter and Garádi, Péter (1974) Investigations on the growth and population-structure of bream (Abramis brama L.) at different areas of Lake Balaton the assessment of mortality and production. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 41. pp. 153-179. ISSN 0365-3005

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Abstract

Investigations were carried out on length-distribution, age-composition and growth of breams collected a t five different areas of Lake Balaton (720 specimens in 1972 and 1403 specimens in 1973). It has been established that: 1. Regression of the total caudal radii of scales on the standard length is linear. 2. On the basis of back-calculated standard lengths from the annuli of scales the growth of bream is fearly rapid. Average values indicate a straightened growth, although in several age-groups considerable variations are observable. Exponential growth in standard length could be represented well by Bertalanffy’s model. Breams of Lake Balaton did not stunt in growth compared with other bream populations inhabiting different Hungarian waters. It is' considered even in European relations to be a fast growing population. According to earlier data referring to the bream stock of Lake Balaton the fast growth is an evident result of the eutrophication and of the quantitative increase of zoobenthos in the open waters, chiefly in Keszthely Bay. 3. Considering the data of earlier years, the ratios of breams of different age caught in Lake Balaton are shifted to the advantage of the youngers, i.e. 2+ age-group is doubled and it already consists of 1/4 of the annual catch (25 per cent). 3+ age-group dominates, and from 3+ to 7+ year-old ones the instantaneous total mortality coefficient proved to be Z = 0.9677. Average annual mortality was 62 per cent and the survival rate was 38 per cent. The sudden increase of 2+ age-group in the catches from the north-eastern basin was on account of the overfishing the population here. 4. Average biomass (B) according to the exponential growth was assessed and its annual production for the most intensively exploited 3+ to 7+ age-groups was derived as 72.6 per cent.

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