Understanding the forces of evolution is more urgent now than at any other time in history, if the negative evolutionary impact on global fisheries is to be prevented, says a leading evolutionary ecologist.
Dr Ulf Dieckmann from the International Institute for Applied Systems Analysis (IIASA) is urging fishery managers to heed warnings that “unnatural” selection is endangering fish stocks and food security worldwide.
This follows on the 200th birthday of Charles Darwin and 150 years after the publication of his seminal work The Origin of Species by Means of Natural Selection.
Dieckmann says commercial fishing over-exploits three quarters of all major fish stocks, including species most important to human consumption. This overfishing does not only reduce the number of fish, but also changes their genetic composition and thus their evolutionary path.
“Although it has long been thought that evolution is a slow process, we now see that the evolution of many commercially fished populations is being tremendously ‘sped up’ in detrimental directions,” says Dieckmann.
Significant evolutionary changes have been documented over just two or three decades. “For example, commercial fishing systematically accelerates maturation. When fish experience a high risk of being captured young, they must produce offspring early in life to transmit their genes to the next generation.”
Responding to this strong evolutionary pressure, many commercial fish species are maturing much younger and are smaller.
For instance 40 years ago the Northeast Atlantic cod, one of Europe’s most important stocks, reached reproductive age at nine to 10 years, whereas today this fish matures in six to seven years. At about half their original weight, early maturing fish produce less than half the amount of eggs, undermining stock stability.
“Similarly, rapid evolution has recently been documented for a dozen other key species.
“This evolution means that fish divert much energy to inefficient reproduction early in life, become more vulnerable to environmental fluctuations and are less capable of recovering from over-exploitation.
“Evolution is driving fish to change in a way that enables them to survive and reproduce in the short term, but in the long term this ‘forced’ evolution makes the species inefficient and susceptible to collapse.”
According to the United Nations, global fisheries provide more than 2,6-billion people with 20% to 50% of their annual protein intake. Understanding how fishing practices change the natural evolutionary patterns of fish stocks is critical.
“If the bottom drops out of a fish stock, as occurred with the Northeast Atlantic cod in 1992, it may take centuries for natural evolution to repair the damage,” says Dieckmann.