01. December 2021 Climatic changes and overfishing depleted Baltic herring long before industrialisation

Historical scene on a Swedish postal stamp. The catch potential of the fishing fleets in the early modern era was hardly inferior to that of today's fisheries. Picture: rook76 – stock.adobe.com

Historical sources indicate that overfishing of the Baltic herring began over 500 years ago and continues to have an impact today

The collapse of the important herring fishery in the western Baltic Sea towards the end of the 16th century was the result of a combination of overfishing and climate change. The researchers see similarities in the current development of German fish stocks. A team of fisheries economists, historians and biologists from Kiel University (CAU), the German Centre for Integrative Biodiversity Research (iDiv) and Leipzig University has reconstructed herring catch levels in the Baltic Sea between 1200 and 1650.

 

The by far most important fishery for autumn spawning herring at that time collapsed within a very short period, without recovering until today. The study, for which they evaluated historical sources, was published in the journal Hansische Geschichtsblätter.

More than a third of the world's commercial fish stocks are considered overexploited or threatened by overfishing. Just this summer, scientists from the University of Hamburg, the Kiel University and the iDiv research centre reported that stocks of cod, one of the most widely consumed edible fish in Germany, have reached a tipping point in the western Baltic Sea, which if exceeded, will probably be irreversible. In the case of cod, climate change has been proven to play a decisive role, with rising temperatures, the cod's capacity to reproduce decreases. Stocks of herring in the western Baltic Sea have also become so depleted that, according to experts, continuing to fish there is neither lucrative nor sustainable.

In a new study, the researchers show - based on historical sources such as toll-books of the Hanseatic City of Lübeck - that a similar interaction between negative environmental effects and overfishing have decimated herring stocks in the western Baltic Sea as far back as the Middle Ages. A cold period in the mid-16th century lowered the average temperature by 0.85°C. As a result, the herring stock lost its productivity, as juvenile fish did not survive. The autumn-spawning herring, until that time the dominant herring subspecies in the western Baltic, almost completely disappeared – and along with it, herring fishing in the region.