| Abstrakt: |
Due to their limited salinity tolerance, the occurrence of freshwater Annex II-fish species such as asp (Aspius aspius), spined loach (Cobitistaenia), bullhead (Cottus gobio), weatherfish (Misgurnus fossilis), bitterling (Rhodeus amarus), and ziege (Pelecus cultratus) was found to be restricted to freshwater and oligohaline-mesohaline habitats (i.e., areas with relatively low salinities), especially in the coastal waters of the German Baltic areas. Mainly anadromous Annex II-fish species such as sturgeon (Acipencer spec.), North Sea houting (Coregonus oxyrinchus), river lamprey (Lampetra fluviatilis), sea lamprey (Petromyzon marinus), allis shad (Alosa alosa), and twaite shad (Alosa fallax) were expected to occur in the German parts of the North Sea and Baltic Sea. However, Acipenser sturio, a species of sturgeon, is considered extinct as a reproductive species in the North Sea region, and the sturgeon species last recorded in individual catches in the Baltic Sea in the 1990s is A. oxyrinchus. At present, the North Sea houting is very rare in the North Sea, while the Baltic houting population (Coregonus maraena) is not protected under the Habitats Directive. Since 1978, a total of 178 records of lampreys have been obtained in the German North Sea areas. Most of the lamprey records (mainly river lampreys) were located in nearshore areas, especially between Helgoland Island and the mouth of the Elbe and Weser estuaries. Recently, 81 individuals of river lamprey and 4 individuals of sea lamprey were recorded in German Baltic waters from 2000 to 2004. Today the main distribution range of allis shad is restricted to the Atlantic coasts of France and Portugal. The record of allis shad in the Strelasund in 1998 was the only specimen of this species caught in German Baltic waters during the last 20 years. Therefore, the species is expected to occur only accidentally in the German waters of the North and Baltic Seas. In contrast, within the German coastal waters (12-nautical mile zone) of the North Sea, there were high-density areas of twaite shad. In total, 6,052 individuals of twaite shad have been caught in the German Bight (Deutsche Bucht) since 1978. Since 1995, however, the catch effort and the percentage of stations with twaite shad records have increased and, in general, there have been more records of this species in the German coastal waters than in the German Exclusive Economic Zone (EEZ). From May 2003 until November 2004, 38 individuals of twaite shad were found at 14 different locations in the German EEZ of the Baltic Sea, northeast of the Rügen Island, as well as in the Pommeranian Bay (Pommersche Bucht) and the Szczecin Lagoon (Stettiner Haff) and its adjacent waters. Fifty percent (50%) of the total twaite shad records originated from the Szczecin Lagoon and adjacent waters. All of them were adult individuals. In the Odra Bank (Oderbank) and in the coastal waters of the Usedom Island, only juvenile individuals of age group 0 were caught; this amounted to 19% of the total number of records. Thirtyone percent (31%) of all individuals of twaite shad (mainly adults) were recorded from the potential Site of Community Interest (pSCI) Western Rønne Bank (Westliche Rönnebank) and adjacent waters. Given the recent records from the German Baltic waters, it is assumed that, after about 50 years of decline, the Baltic population of twaite shad has been increasing since the middle of the 1990s. The observed status of the populations of Annex II-fish species in the German waters of the Baltic Sea and North Sea indicate that the study of their distribution and the trends in their population development must be continued on the basis of an international cooperation, especially with the new EU Member States of the southern Baltic. [ABSTRACT FROM AUTHOR] |
