Towards better Understanding of Successful Management of the Gulf of Riga Herring Stock

Abstract

The Baltic herring is one of the key elements of the pelagic ecosystem of the Baltic Sea, being of the most important commercial species of the sea. The structure and dynamics of herring populations (stocks) have been assessed and managed on international level since 1970s. Since 1990, all local herring populations have been combined and assessed as one stock (Central Baltic Herring in Sub-divisions 25–29 and 32). However, the continuously decreasing trend in stock biomass throughout almost 30-years period of observations indicates the failure of the stock management implementation of the scientific advice. The separate assessments of different stocks and results of hydro-acoustic surveys of different sub-units (herring in Sub-divisions 25–27, Sub-divisions 28, 29 and 32 and the Gulf of Riga herring) have revealed rather different situation within combined assessment unit: e.g. fishing mortality of the Gulf of Riga herring has decreased while a sharp increase in mortality is observed in the herring stocks of the North-eastern Baltic (Sub-divisions 28, 29 and 32). At the same time stock abundance and biomass of the Gulf of Riga herring have increased to record high in early 2000s allowing also higher catches. It is concluded that only separate analytical assessment of local populations combined with regular acoustical surveys and following different protection measures have proved to be a successful way in managing the herring stocks. Joint assessment and management of several populations with different structure and dynamics as one combined stock do not allow revealing the real situation and trends in its parts.