STOCK CONDITION, POPULATION DYNAMICS AND PECULIARITIES IN BIOLOGY OF THE TURBOT (Psetta maxima L.) IN RELATION WITH MEASURES FOR ITS RATIONAL EXPLOITATION OFF BULGARIAN BLACK SEA COAST

摘要

Turbot (Psetta maxima L.) is demercal species with primary importance in the Black sea region as regards its high commercial value and specific ecological state in the marine ecosystem. The level of its stocks is highly dependant on fishing pressure and other far-reaching anthropogenic activities, as pollution, with negative influence on the whole ecosystem. For turbot stock assessment bottom otter trawl and 'swept area' method have been used and stock in front of the Bulgarian coast has been assessed as 1500-16001. The highest average catch per unit area (CPU A kg/km~2) for northern part has been detected in stratum 35-50 m - 333 kg/km~2 (winter), and in southern part of the coast the highest average CPUA was 292.88 kg/km~2 in stratum 50-75 m (spring). According to the research findings, asymptotic length varies from L_∞ = 81.26 (2006, winter), k = 0.14 year~(-1), t_0 = - 1.09 to L_∞ = 91.503 (2007, spring), k = 0.1368 year~(-1), t_0 = -1.61. The growth of turbot has been found allometric (from n = 3.07 to 3.2932). Index of relative importance of different nutrition components in the turbot stomachs was calculated. Highest IRI % belongs to the whiting Merlangius merlangus N o r d m. - during winter investigations and to the crustacean Crangon crangon L. - during spring period. This paper emphasises the importance and development of different management strategies, provides scientific data for regulation of harvest and scientific advice on sustainable utilisation measures.