RESUMEN
Based on the model describing the dynamics of the number of generations of fish during the life cycle, the influence of growth and maturity on the biological and commercial productivity of conditional populations of Caspian sturgeon, formed from 1.0 million specimens of yearlings, was studied. On the biomass of conditional sturgeon populations, their gross output and catch are influenced by the length of yearlings, the size and age of maturity, the periodicity of spawning, the rate of linear and weight growth of individuals, and the degree of stocks catching. The highest yield of biomass and catch, obtained from 1 million yearlings, is observed in Beluga (Huso huso), then Ship Sturgeon (Acipenser nudiventris), Russian sturgeon (Acipenser gueldenstaedtii), Stellate Sturgeon (Acipenser stellatus) and sterlet (Acipenser ruthenus).
RESUMEN
The seasonal variation of fish species composition and abundance in gillnet catches (14-90 mm knot-to-knot) from the Greek part of the transboundary Lake Doirani was studied during the period 2006-2007. A total of 8,419 specimens weighting 182.3 kg and belonging to 9 species were caught. Catch composition differed with season. Thus, Rhodeus meridionalis dominated in terms of NPUE the spring, Perca fluviatilis the summer and Alburnus macedonicus the autumn and winter catches. Cyprinids were generally the most abundant, with the cyprinids:percids biomass ratio ranging from 1.7 in summer to 14.8 in winter, supporting the eutrophic character of the lake. Richness and Shannon-Wiener diversity and evenness indices differed seasonally (ANOVA; p < 0.05). The abundance-biomass comparative (ABC) curves showed that fish communities were dominated by one or a few opportunistic species (e.g. Rhodeus meridionalis, Alburnus macedonicus), which while dominated in number did not dominate in biomass, being small bodied.