Function: Population dynamics of commercially used fish

BALTIC SEA

The populations of economically important fish species have varied widely since the 1960s. The population of sprat has been quite large in the 2000s but the population size has fluctuated a great deal during the last four decades. In 2012 the spawning stock biomass was about 900 000 kg.  The reasons for strong fluctuations and the threats for the population are yet insufficienlty known.

The cod population was mutlifold compared to the population today in the first half of the 1980s. In 2012 the spawning stock was approximately 150 000 kg. The population of cod has suffered from intensive fishing and poor breeding conditions such as lack of oxygen in the spawning basins and low salinity in the Baltic Sea.

The population of the Baltic herring was 1.7 million kg in 2012. The population was at that level in the 1970s and the 1980s but there was a strong decreasing trend in the end of the 1990s and the beginning of the 2000s. The populations of the Baltic herring vary quite a lot in different parts of the Baltic Sea. In the Baltic Proper and the Gulf of Finland the spwaning stock has decreased by more than 50% in the last fourty years. In the Bothnian Sea the spawning stock has, on the other hand, increased from  200 000 kg to a million kg in 1973-2012. Despite the intensive fishing the population of the Baltic herring has not decreased strongly. The reason for this is probably spawning in shallow water and the fact that most fished herrings are adults. The eutrophication, low salinity and the strong sprat population might, nevertheless, cause a decrease in the herring population.

Fish atlas. Game and Fisheris Research.