Cod stocks in the western Baltic Sea are at an historic low. If fishing continues, they could collapse to such an extent that they are irretrievably lost - if not biologically, then at least for the 400 German commercial fishers whose livelihoods depend on these animals, among others. Unfortunately, this would not be the first time that humans have depleted the sea of a fish stock: this has already occurred once before in the Middle Ages. A particularly comprehensive study from Kiel reconstructed catch figures between 1200 and 1600. Even then, long before industrialisation, a combination of overfishing and external environmental factors drove the population decline. Around 1500, the average temperature dropped by 0.85°C due to a cold period, meaning that the autumn-spawning herring (Clupea harengus), then a major food source for the flourishing Hanseatic League, no longer produced enough juveniles to survive the winter. Populations collapsed rapidly, destroying the livelihoods of thousands of fishers. On the Swedish Peninsula alone, 45,000 people depended on fishing at that time. To this day, more than 400 years after complete overfishing, only the spring-spawning herring (which is also overfished today) occurs in the Baltic Sea. We can learn from this history and, this time, look beyond the dinner plate towards the future. Since 2015, the estimated spawning stock biomass of cod (Gadus morhua) has remained below a critical threshold. Commercial cod fishing has therefore been banned since 2022, with the exception of approximately 500 tonnes of permitted bycatch. Recreational fishers are currently restricted to a bag limit of one cod per day. It remains to be seen whether these measures will suffice to prevent the socio-economic and ecological system from permanently destabilising. Sources: Lehmann, O., Schmidt, J., Voss, R., (2021): „De vorbisteringhe deß heringheß uthe deme Sunde“ - Indizien für eine vorindustrielle Überfischung des Ostseeherings. Hansischen Geschichtsblätter (Band 139/2021) European Commission: Fishing opportunities in the Baltic Sea for 2023.
