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Decades of Overfishing Have Genetically Stunted Baltic Cod

Genetic analysis shows that decades of preferential fishing of larger cod triggered earlier maturity below 20 centimeters, blocking population recovery.

Image
Ein Dorsch, auch Kabeljau genannt, in einem Aquarium des Geomar-Instituts in Kiel

Overview

  • Eastern Baltic cod once exceeded one meter in length and 40 kilograms but now reach sexual maturity at under 20 centimeters.
  • A fishing moratorium imposed in 2019 has failed to reverse declines in both size distribution and overall population.
  • Researchers analyzed otoliths from 152 cod caught between 1996 and 2019 in the Bornholm Basin to map age, growth and genetic shifts.
  • Selective removal of large individuals has nearly eradicated fast-growing genotypes, demonstrating fisheries-induced evolutionary change.
  • Smaller cod programmed for early reproduction yield fewer offspring, exacerbating ecological strain on the Baltic Sea.