Effect of environmental variability and spawner characteristics on the recruitment of Baltic herring Clupea harenguspopulations

We analyzed recruitment–environment relationships for 5 distinct Baltic Sea herring stocks inhabiting the areas of the Western Baltic (WBH), the Main Basin (MBH), the Gulf of Riga (GRH), the Bothnian Sea (BSH) and the Bothnian Bay (BBH). A number of hydro-climatic and biological predictors were tested for their effect on recruitment. Temperature was determined to be an important predictor for 3 of the stocks (MBH, GRH and BSH). However, spawning stock biomass was the major factor explaining recruitment for GRH and weight-at-age of the spawners was an important predictor of MBH recruitment. For 2 out of 4 stocks for which complete zooplankton data were available (BSH and MBH), food supply was also a significant predictor, suggesting that changes in climate and/or food web structure may indirectly affect herring recruitment via prey availability for the recruits or spawners. Our results emphasize both similarities and differences in the main regulators of recruitment dynamics for the 5 stocks that should be taken into consideration in the development of area-specific management strategies throughout the Baltic Sea basin.