Untersuchungen zu biologischen Schadstoffeffekten bei Nordseefischen: Langzeitdaten zum Auftreten von Lebertumoren bei der Kliesche (Limanda limanda)

Data are presented on the spatial distribution and long-term temporal trends in the occurrence of neoplastic liver lesions of North Sea dab (Limanda limanda) in the period 1988 to 2001, obtained in the framework of the regular fish disease monitoring programme carried out by the German Federal Research Centre for Fishery. Highest prevalences consistently recorded in the first part of the period occurred in the German Bight, at the Dogger Bank and at sampling sites off Humber and Wash. In contrast, stations in the northern North Sea (e.g. in the Firth of Forth area) were always characterised by low prevalences. Particularly during the first years of observation, a clear and general decrease in prevalence could be observed, that was most pronounced in the hot spot areas German Bight and Dogger Bank compared to the Firth of Forth. Current data reveal that, due to the decrease, spatial differences between sampling sites are now much less obvious than at the beginning of the studies. Limited chemical data available suggest that the temporal decrease in prevalence of liver tumours and their precursor stages generally correspond with the decrease in organic contaminants in dab livers as well as in water and sediments. However, the spatial variation in prevalence recorded can not entirely be explained by contaminant levels. For instance, the prevalence was continuously low in the Firth of Forth area wheras the contaminant levels in dab were comparatively high. The opposite feature was observed at the Dogger Bank. Future studies will therefore address the role of other host- and site-specific factors potentially involved in the aetiology of the disease.

Mehr Nachwuchs bei Nutzfischarten der Nordsee, ausser beim Kabeljau

Ninety-one half-hour tows with the Grande Ouverture Verticale bottom trawl (GOV), 111 hydrographic stations and 100 catches with the Methot-Isaac-Kidd Net (MIK) were this years’ contribution of “Walther Herwig III” to the IBTS in various areas of the North Sea. Preliminary results indicate that especially haddock and, to some extent, whiting and Norway pout generated an ample 1999 yearclass. Indices for herring are also well above last years’ index whereas the cod indices indicate no substantial improvement of the stock. Largest concentrations of herring larvae were found in Moray Firth and west of the Dogger Bank/The Gut area. Temperatures of the North Sea were found to be above the long term means: 1 Centigrade on the open sea and up to 3 Centigrades in coastal areas. This years’ “WH III” IBTS activities at sea were considerably hampered by rough weather

Deutsche und internationale Bestandsuntersuchungen an Heringen mit hydroakustischen Methoden

The international hydroacoustic herring survey in the North Sea is carried out since the early eighties with Dutch, Scottish, Danish und Norwegian contribution. Since 1994 Germany also participates in this survey on a regular basis and has taken over a sector in the easter part between the Dogger Bank and the Danish coast. This area is known for the abundance of chiefly juvenile herring and sprat. During the 1995 cruise some 420000 t of herring were found here, most of them being juveniles of age group I. Analyses of plankton hauls showed that planktonic echos were not caused by juvenile herring, instead the echos were apparently produced by small pelagic gastropodes of the genus Spiratella.