Fewer Baltic salmon are now dying from the puzzling M74 syndrome, but salmon deaths could increase again. Despite intensive studies it is still not clear what causes the syndrome, which affects newly hatched salmon fry. Researchers strongly suspect that the explanation lies in a number of complex interacting factors in the Baltic Sea. Precautionary treatment with vitamin B1 reduces mortality in salmon hatcheries, but this method offers no cure for wild salmon. Baltic sea trout is also affected by M74, a recent conference in Stockholm concluded.
"It is becoming increasingly obvious that M74 is a complex environmental problem that demands extensive interdisciplinary co-operation", says associate professor Bengt-Erik Bengtsson, chief scientist of the project at Stockholm University.
The syndrome is named after the year it was discovered, 1974. M stands for "miljöbetingad", i.e. "environmentally related". In a four-year project, a group of researchers commissioned by the Swedish Environmental Protection Agency, the National Board of Fisheries, the Swedish Council for Forestry and Agriculture Research, the World Wide Fund for Nature (WWF) and the Power Board, have tried to trace the cause of the syndrome.
"The M74 syndrome was a problem that was left out of the game in Research Sweden. That's why five government authorities and organisations started the project, which has now come to an end. A number of questions still need to be answered, and we must find a sponsor to finance further research", says Rolf Annerberg, head of the EPA.
Death usually occurs in afflicted salmon fry a few days after the first symptoms are seen. In 1993, when the frequency of M74 was at its peak, the syndrome claimed up to 90 per cent of farmed salmon fry in some rivers. In recent years, the incidence has been considerably lower. Researchers long suspected a link with environmental pollutants such as chlorinated organic compounds (PCB, dioxins, etc.), no such link has not been confirmed. No evidence has been found that heavy metals, bacteria or viruses are associated with M74.
There seems to be a link between M 74 and pale colour in Baltic salmon roe. There also seems to be a connection between the stock of sprat, a prey fish, and M74. Some researchers suspect that the relation between sprat and other fish is affected by excessive nutrient enrichment of the Baltic sea as well as by intensive fishing of Baltic cod. In hatcheries, salmon roe and fry can be treated with Vitamin B1 (thiamine). But there is no method for treating the threatened stocks of wild salmon.
"It is most likely that M74 is caused by several interacting factors, which stem from our influence on the Baltic ecosystem. These factors cause effects to be reinforced and can lead to severe environmental problems. Such interaction is hard to establish and increases the demand for basic ecological research in the Baltic sea. Even if this particular research programme has come to an end, it is important that such research continues", says Bengt-Erik Bengtsson.
Baltic sea trout, which is a relative of salmon, is also affected by M74. Reproductive problems in Baltic cod can, however, be explained by poor oxygen conditions in its feeding grounds and heavy fishing pressure.
For further information, please contact:
Bengt-Erik Bengtsson, Stockholm University, 46-8-674-72-12,
bengt-erik.bengtsson@itm.su.se, bebben@trosa.mail.telia.com
Press service:
Anna Bonta-Anger, 46-8-698-1084, 0708-299-369, Anna.Bonta-Anger@environ.se
Suzanne Kolare, 46-8-698-16-97, 0708-26-16-97, Suzanne.Kolare@environ.se
Journal
AMBIO