Fisheries in decline due to ‘unnatural’ selection

Understanding the forces of evolution is a more urgent need now than at any other time in history, if the negative evolutionary impacts of global fisheries are to be prevented, according to a leading evolutionary ecologist.
Speaking on Charles Darwin`s 200th birthday and 150 years after the publication of his seminal work ‘The Origin of Species by Means of Natural Selection`, on Thursday, Dr Ulf Dieckmann from the International Institute for Applied Systems Analysis (IIASA) urged fishery managers to heed warnings that ‘unnatural` selection is endangering fish stocks worldwide.
“Today, commercial fishing overexploits or maximally exploits three quarters of all major fish stocks, including species most important to human consumption. This overfishing is not only reducing the number of fish, but is also changing their genetic composition and thus their evolutionary path,” says Dieckmann.
“While 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 ‘speeded up,` in detrimental directions,” says Dieckmann. “Significant evolutionary changes have been documented to occur 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 than they used to. By example, forty years ago the Northeast Atlantic cod, one of Europe`s most important stocks, reached reproductive age at around 9-10 years, while today this same fish is maturing in 6-7 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, they become more vulnerable to environmental fluctuations and 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 UN, 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 therefore critical.
“If the bottom drops out of a fish stock, as occurred with the northern cod in 1992, it may take centuries for natural evolution to repair the damage,” concludes Dieckmann.