Die Reproduktion von Dorschen (Gadus morhuaL. undGadus morhua callariasL.) in der Ostsee unter besonderer Berücksichtigung der Arkonasee : Teil 2: Statistische Analysen zum Anteil reproduktiv aktiver Dorsche im Bezug auf gebietsspezifische Unterschiede und Gemeinsamkeiten, sowie deren mögliche Ursachen

Abstract

Surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea from 1993 to 2003. Part I of the article describes the general maturity development and the spawning activities in the western Baltic Sea, the Arkona Sea and the Bornholm Sea. The studies suggest that two types of spawner can be distinguished, the spring spawner in the western Baltic Sea and the summer spawner in the Arkona Sea and the Bornholm Basin. The descriptive analysis is supported by statistical studies presented in this article. It is shown, that the proportion of spawning individuals is significantly higher in summer than in spring in the ArkonaSea and the Bornholm Sea. Furthermore, it is shown that reproductive mixing of both types of spawner is possible in the Arkona Sea in May/June due to the hydrographical conditions in the Arkona Sea which were suitable in 8 of 10 years for successful reproduction of both Baltic cod stocks, and that spatial expansion of spawning activities of the eastern Baltic cod stock into the Arkona Sea is positive correlated with the size of spawning stock in the Bornholm Sea.