Humanity influences evolution

Laboratory experiments on fish have shown that the age of sexual maturation can be altered in the course of only four generations. This is extremely rapid, in that evolution is something that usually takes place in a temporal perspective of millions of years.

Changes in the temperature of the ocean could have serious consequences for fish on the coast of Norway. “Both fishing and pollution have turned human beings into one of the driving forces of evolution. Now we need to know which species we are in the process of modifying and whether they are robust enough to be able to deal with future climatic changes,” says Christian Jørgensen of the Department of Biology, who is using advanced computer software to simulate evolutionary processes in fish and to study how their physiology and behaviour are altered when changes occur in their living conditions.

Rapid changes

Ecosystems have always been liable to undergo major dramatic changes, while many individual species are highly adaptable. Research has shown that the age of sexual maturation in the cod has changed in the course of the past 70 years. In the 1930s, cod became sexually mature at the age of ten or eleven years, while today they mature when they are eight years old. Although evolution is taking place rapidly, it is difficult for scientists to predict how fish will respond to the climate changes caused by human beings which we have witnessed during the past few years.

The living conditions of fish can be changed quite dramatically if the temperature of the sea rises. A typical consequence for marine species is that they alter their distribution range. If this happens, the species concerned may overlap with other species more than before, which may affect these species in turn. The consequences may include changes in the food available to the fish, or that they are faced with new predators. Such factors affect mortality and growth and may also have consequences for our own access to fish resources.

We fish too much

Jørgensen emphasises that it is difficult to predict changes of this sort. “An ecosystem is a network in complex balance. There are so many mutual dependencies that changing just one component may have serious consequences for the whole system, while other changes will have virtually no effect at all. This is why it is important to predict how fish species will evolve, so that we can suggest which of any set of scenarios is likely to occur. A report drawn up by the UN Food and Agriculture Organisation (FAO) shows that in a global perspective, fishing has reached the upper limit of sustainability.

“More than a quarter of fish stocks are in a critical situation, while half of them are being maximally exploited. This means that there is an enormous pressure to catch fish all over the world. In our models we can see that fishing changes the cod as a species. Modern fishing has “created” a small fish which may be very sensitive to changes in the length of its migrations,” concludes Jørgensen.

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