Overfishing has caused cod to halve in body size since 1990s, study finds

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Source: Guardian

Overfishing has led to a collapse in the eastern Baltic cod population, but over the past three decades the size of the fish themselves has also been dramatically and mysteriously shrinking.

Now scientists have uncovered genomic evidence that intensive fishing has driven rapid evolutionary changes that have contributed to these fish roughly halving in average body length since the 1990s.

The “shrinking” of cod, from a median mature body length of 40cm in 1996 to 20cm in 2019, has a genetic basis and human activities have left a profound mark on the population’s DNA, the study concluded.

“When the largest individuals are consistently removed from the population over many years, smaller, faster-maturing fish gain an evolutionary advantage,” said Prof Thorsten Reusch, head of the marine ecology research division at Geomar Helmholtz Centre for Ocean Research Kiel and senior author of the research.

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Read more: https://www.theguardian.com/environment/2025/jun/25/cod-shrinking-size-overfishing-study