Herring and sprat growth changes in the Central Baltic Sea

No abstracts are to be cited without prior reference to the author.

Oceanographic conditions in the brackish Central Baltic Sea are strongly linked to the atmospheric forcing and the unusual period of persistently high NAO-index values since the late 1980s resulted in an increase in average water temperatures and decreasing salinities. Changes in temperature and salinity have resulted in a dominance change in the mesozooplankton community from Pseudocalanus sp. to Temora longicornis and Acartia spp. Similar to the copepod community, the Central Baltic fish community shifted from a cod (Gadus morhua) dominance during the 1980s to a sprat (Sprattus sprattus) dominance during the 1990s. Further, the commercially important pelagic fish species herring (Clupea harengus) and sprat exhibited drastic fluctuations in growth. Using time-series data in Principal Component and Correlation Analyses we investigated the importance of the food supply as well as competition on condition of Central Baltic pelagic fish species. Our results indicate a combined effect of changes in the feeding environment and increased competition on condition of herring, while sprat condition appeared to be primarily determined by intra-specific competition.