A new research points to intensive fishing as guilty about decreasing Baltic cod, which has gone from over one meter long to just 50 centimeters in recent decades.
A genetic autopsy of the eastern Baltic Baltic confirmed what fishermen and biologists have suspected for years: relentless commercial fishing not only reduced the formerly abundant population, but also permanently reprogramed the DNA of the species, favoring atrophied growth.
Published on June 25 at Science Advances, an international team led by Marine Ecologist Thorsten Reusch of the Geomar Helmholtz Center in Germany analyzed 152 file otolites – small ears bones that register the annual growth of a fish – taken from cod captured between 1996 and 2019.
During this period, the maximum length of the Baltic Cod descended from more than one meter to just 50 centimeterswhile the average weight descended to a fraction of palm size in relation to historical levels.
By sequencing the genome of each specimen, scientists identified dozens of genetic variants linked to body size. Large fish variants have been gradually disappear from the genetic setas industrial fishing captures the largest individuals year after year. “Human capture has one of the most powerful selection pressures in nature,” said Reusch.
Cod in the Baltic was already so abundant that the catches reached a peak 400 000 tons per year In the late 1980s. But as the networks became more efficient, the small youths slid down the designs designed to retain only commercial size fish.
This practice effectively rewarded slow growth genes and early maturity as it punished those of large size. The EU finally imposed an emergency moratorium on East Stock fishing in 2019, after the surveys showed a population collapse, but cod remained tiny.
The team tested alternative explanations, such as heating seawater, pollution and decreased prey. Although the highest temperatures can reduce the size of the fish, the model showed that the decline observed greatly surpassed what the climate itself could cause, the.
The loss of genetic diversity entails long -term ecological risks. The larger cod historically served as the main predator and sustained a fishing of € billion; Smaller fish produce fewer eggs and are more vulnerable to environmental shocks. If large -growing codfish disappears completely, “the population may never recover their previous stature, even if fishing is over,” the authors warn.
