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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.

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.