High speed evolution along the Norwegian coast

TRAWLING IN THE LAB: ‘The worst-case scenario is that we will lose the North-East Arctic cod as we know it today,’ says Professor Mikko Heino. He leads the EvoFish research group, which is investigating the evolutionary effects of fishing. Beatriz Diaz Pauli and Chandana Nissanka try to simulate overfishing in an experiment using guppy fish from Trinidad. Foto: Eivind Senneset

Text & photo: Eivind Senneset

The fact that species are disappearing and becoming extinct as a result of human activity no longer surprises us. Our actions affect not only which species die but also those that survive. The pressure caused by modern trawling is so immense that researchers now say that we are provoking evolutionary changes in the stocks we harvest. Or, to put it another way, we are fishing so intensely that the fish’s genetic material is changing. In the 1960s, we came close to wiping out herring. In the 1980s, the Canadian cod stocks collapsed. Today, the coastal cod north of Møre is categorised as highly endangered. According to the UN’s Food and Agriculture Organisation, 75% of the world’s fish stocks are either fully exploited, over-exploited or have collapsed.  

‘In agriculture, the genetic material of the best animals is preserved. In fishing, the opposite is the case,’ says Professor Mikko Heino, a researcher at EvoFish (Evolutionary Fisheries Ecology) at the Department of Biology, University of Bergen

Farewell to the North-East Arctic cod?

Evolution is a slow process. Advanced life forms do not change so fast that significant changes can be observed during the lifetime of a human generation. At least, that has been the prevailing opinion until now. Now, however, researchers are beginning to realise that this is precisely what is happening right off our own coast. In the 1930s, the North-East Arctic cod became sexually mature at around nine years of age. Today, however, the fish matures after only six or seven years. It also grows to a significantly smaller size.

‘We are talking about a growth reduction of up to 50%,’ says Professor Heino. He is convinced that these changes are due to evolution – provoked by decades of industrial fishing.

‘Natural selection led to fish growing to full size and becoming sexually mature at a late age. But modern trawlers that sweep the ocean floor are extremely effective predators. We are in the process of reversing thousands of years of natural evolution,’ he says. ‘In relation to natural predators, size is an advantage for the fish. But growth is a long-term investment that involves postponing spawning. If you see that this investment is no longer proving profitable, you choose a new strategy. If you know that this is the last day of your life, you live your life accordingly – and spawn earlier.

When the fish use their energy to mature instead of to grow, it is inevitable that this will result in smaller fish. This has consequences for both the fish themselves and for those who make a living from them. From a commercial perspective, the North-East Arctic cod is the most valuable species in Norwegian waters. It may now be about to change into something more like North Sea cod, which lacks the ability to grow very large.

‘The worst-case scenario is that we will lose the North-East Arctic cod as we know it today.’

Hazardous waters

The North-East Arctic cod is an extreme case. However, it is believed that similar evolutionary changes have been detected in both plaice and humpback salmon. The research group behind these findings is EvoFish (Evolutionary Fisheries Ecology) under the leadership of Professor Mikko Heino. Since autumn 2007, the group has carried out research on the effects of fishing – and has found even more reasons to apply the precautionary principle in resource management. We have long regarded the sea as an inexhaustible larder. The sea was so black that harvesting all the fish in it seemed impossible. But then came the herring crash in the 1960s. The fishermen experienced a serious reality check.

The reason behind this eye-opener was the introduction of new and more effective equipment. Since then, fishing equipment has become even more uncompromising. The worst offender is the trawl, which catches everything that is swept into the net. While there are regulations stipulating minimum sizes for fish that can be legally caught, no upper limits exist.

Fish two, kill three

When the largest individuals in a group are removed decade after decade, it is perhaps not surprising that the group adapts to the realities of the situation. But – as researchers are quick to point out – that is only half the story; for the fact is that selective fishing of large individuals also contributes to a significantly higher rate of natural mortality. ‘In the ocean you live with a constant risk of being devoured by the bigger fish,’ says Christian Jørgensen, another researcher in the EvoFish group.

'To be small, grow quickly and reproduce at a rapid rate are all factors that contribute to a higher mortality rate. Fishing provokes the risk attributes of each and every one of these factors. You may fish two, but you kill three,’ says Mr Jørgensen, and refers to the example of the cod stocks off Canada, which collapsed at the end of the 1980s. The annual mortality rate was estimated to be 20% around 1980. The latest measurements, which were taken several years after the stock had been protected, show a tripling of the natural rate of mortality.

‘Many factors can play a role, but it seems unlikely that this increase is not related to fishing.’

The Lofoten fisheries on the wane

Old catch statistics show that the North-East Arctic cod travelled as far south as Lindesnes a hundred years ago, which involves a 2,100 km-swim from the Barents Sea. Once they had spawned, the fish swam back again. The distance of this spawning migration round trip was as a tenth of the circumference of the planet Earth. Swimming such a distance demands considerable energy reserves. Large fish can manage the journey, but small fish would be out of their depth, so to speak. Smaller and smaller individuals are migrating shorter and shorter distances. In the early 1990s, you could still catch North-East Arctic cod off Sotra, but this is unheard of today. Even off Møre and Lofoten –historically the most important fishing grounds – the North-East Arctic cod has become a less frequent visitor. ‘In the future, the Lofoten stock itself may be decimated. Perhaps the North-East Arctic cod will choose to spawn along the Finnmark coast instead,’ says Christian Jørgensen.

Such a change in spawning habits would have added ripple effects on the stock. There are big differences in climate between Lofoten and Finnmark, and this will affect the population dynamics in the form of more markedly good and bad years.

'In this respect, the changes we are now seeing could prove important in relation to both Norway’s regional policy and its foreign policy. Perhaps Norwegian fishermen will have to find new fishing grounds further north, perhaps we may have to find a new sharing system with Russia when the stock retreats further into Russian waters,’ says Mr Jørgensen.

 ‘Fish less!’

In the 1930s, we harvested 500,000 tonnes of North-East Arctic cod. After World War II, when several years without fishing had led to a dramatic increase in stocks, we netted one million tonnes. Today that figure is around 600,000 tonnes. In other words, there has been no dramatic change in the total catch for almost 80 years, but the catch as a percentage of the stock has gone through the roof. This is because the exploitable stock of North-East Arctic cod has been halved during the same period. However, according to today’s measurements, the North-East Arctic cod is still sustainable and can in theory tolerate even larger catches. But these measurements do not take evolutionary considerations into account, and this is something the researchers believe may prove to be a problem:

‘Evolution is not rational. In the short term, we may be able to predict what changes will occur, but in the long term we don’t have a chance. If we are careful and conserve the large fish with good genes, then we may perhaps delay the evolutionary changes until we understand more about what is going on,' says Mr Jørgensen.

But there is one thing the researchers are sure about: while intense pressure on fish stocks could provoke changes in the course of only ten years, it will take far longer to reverse the trend. Professor Heino estimates that it will take a fishing ban lasting at least 50 years to reverse the effect of ten years of fishing. He is now calling for alternative management strategies combined with technical solutions that prevent the trawls from catching the largest individuals. Although the technology exists, it is the political will that is lacking. This is partly due to the fact that far from everyone is convinced that the changes now being observed are in fact evolutionary. The critics are demanding genetic proof.

‘Give us five years and we’ll have the proof, too,’ says Professor Heino.

This article is published in Hubro 3/2009

CHANGING FISH: The stock of North-East Arctic cod has halved since 1930. Researchers believe that the pressure on fish stocks is so intense that it is changing the fish's genetic material.