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Public Radio's Environmental News Magazine (follow us on Google News)

Salmon Parasite

Air Date: Week of

Norway's Laerdal river has just been deliberately poisoned with rotonone in order to control a deadly parasite, Gyrodactylus salaris. The tiny worm was infecting scores of Atlantic salmon, but while rotonone destroys the parasite, it also kills most fish and many other acquatic species. The treatment has been controversial since its introduction more than 20 years ago and its use in the river has brought opposition to a head. Vera Frankel has our report.


CURWOOD: In the face of the worldwide collapse of natural fisheries, fish farming has been held out as a partial solution. But the crowding of fish together in pens can increase the spread of disease. In Norway, a massive outbreak of the parasite Gyrodactylus salaris among Atlantic salmon is being blamed by some scientists on aquaculture. Whatever the cause of the outbreak, Norwegian authorities are taking drastic action. To control the parasite, one of Norway's mightiest fishing rivers has just been poisoned with about 100 gallons of rotonone, a naturally occurring alkaloid familiar to gardeners as one of the more environmentally friendly pesticides. While rotonone destroys the parasite, it also kills virtually all fish and many other species of aquatic life as well. The treatment has been controversial since its introduction with the advent of fish farming more than 20 years ago, and its use on this river, the Laerdal, has brought opposition to a head. Vera Frankel has our report.

(Running water)

FRANKEL: The Laerdal River rushes through the magnificent fjord country of western Norway. It's a favorite of Norwegian royalty and, as it happens, of British aristocracy, who've been fishing the Laerdal since the 19th century. A few weeks ago a crew of 70 men poured about 100 gallons of poisoning rotonone into a 15-mile stretch of the river teeming with salmon and trout. Another group stood by along the banks to remove the fish as they rose gasping and convulsing to the surface. The treatment will be repeated in August, and the river, the 25th to be treated with rotonone, will remain closed to fishing for 5 years. Only then will the Laerdal be restocked with salmon and trout. Antonio Pileo, a research biologist at the University of Oslo, is one of many scientists and conservationists galvanized by the fate of this very special river, who oppose controlling the Gyrodactylus parasite with rotonone.

PILEO: You have to realize that a river is not only a place for salmon to live. The river is much more. It's a whole ecosystem. There is a lot of other fish species there, there's a lot of invertebrates living there. And I think when you use the rotonone you wipe out most of that.

FRANKEL: The anti-rotonone camp faces formidable obstacles. Changing long-established practice on the one hand, and on the other the importance of salmon to the Norwegian economy. Sport fishing alone is worth perhaps $16 million a year to local communities, and Norway accounts for about two thirds of the world's farmed salmon, about 300,000 tons annually. The official line is that wholesale poisoning of infested rivers is far preferable to risking the spread of the parasite, which grazes on the skin of the salmon and leaves it open to infection. But even those who favor this describe it as the lesser of 2 evils. Or, as the Norwegian expression has it, a choice between plague and cholera. Tor Atleymo of the State Veterinary Institute.

ATLEYMO: Rotonone itself is of course a bad thing. But the program itself, yes, I support it. Because this parasite is so harmful to the Norwegian salmon populations, and it's still spreading to new rivers every year. So we have to stop it some way. And today we only know about that method: to kill all the fish and wipe out the parasite.

(Flowing water)

FRANKEL: In Antonio Pileo's dank subterranean laboratory at the University of Oslo, fish of different species suffer in the cause of his research. Dr. Pileo and his colleagues are studying the biological consequences of acid rain, and in the process they think they might have found a less destructive and wasteful treatment for the salmon parasite. Having noticed that salmon in even mildly acidified rivers were free of the parasite, Dr. Pileo suspected that aluminum leaching into the water, one of the toxic side effects of long-term acidification, might be the reason. He exposed fish to a short, sharp dose of the metal, and in the lab at least it looked good.

PILEO: What we found was very interesting. Firstly, we found that we could eliminate the parasite within a few days. And even more interesting, we didn't kill any salmon. And our comparative studies have shown that the Atlantic salmon is the most vulnerable species for aluminum. So if we can save salmon we can save all other fishes. And therefore, we propose that we have a good idea for an alternative method, because rotonone is, you know, is killing more or less all the life in the river.

FRANKEL: But this approach seems to have aroused little if any official interest, and even antipathy in some quarters. Tor Atleymo of the State Veterinary Institute is positively scathing in his dismissal of the aluminum option. Lab conditions he insists are one thing, but a river is something else.

ATLEYMO: In some areas of a river, the water is running away within a few seconds, and other parts the water can be in the same position for hours. So how sure can he be that they have the needed concentration everywhere at any time during treatment? That's extremely difficult.

FRANKEL: There is of course another strategy: to do nothing at all, in the hope that the salmon might develop immunity to the parasite given time. That's the option favored by Sigrun Ringwald of the Norwegian Society for the Conservation of Nature.

RINGWALD: In other countries the salmon are resistant against this parasite. And in Norway they haven't really given the salmon the time to get this resistance, because you treat the river with poison before you see if the fish get resistant against it. It would do better to leave the salmon entirely alone than to use rotonone to kill all the fishes in the river.

FRANKEL: But the government maintains that rotonone does not kill all life in the rivers, only fish in the lower reaches of the river frequented by the Atlantic salmon, and that other forms of life recover relatively quickly. Critics of the government can't rely on the experience of other countries because the salmon parasite is not a problem elsewhere. Steinar Hermanson of the Ministry of Environment acknowledges that theirs is a uniquely Norwegian solution to a Norwegian problem, and he's clearly used to dealing with critics of the program.

HERMANSON: This argument has been our headaches for several years when we are doing this treatment, because of course to use rotonone in rivers like this, it's really a very difficult environmental political question, and a difficult ethical question, too. So it's really a dilemma how we should handle this parasite, all this has been.

(Rushing water)

FRANKEL: Norway's salmon rivers are far more than an economic resource. Like any powerful force of nature, they also play an important part in shaping a sense of national identity. In Norway, even those who support the use of rotonone are uneasy about dumping poison into waterways. Even they are in no doubt that however successful the treatment, the days when a rich Englishman could catch 22 salmon in one epic afternoon on the Laerdal River -- Edward Portman was his name, and his record still stands -- are gone forever. For Living on Earth, I'm Vera Frankel.

(Music up and under)

CURWOOD: Our report on the salmon parasite was produced by Tony Samstag.



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