– A local stock can disappear in a trawl move. Then there will be major effects on the entire ecosystem, says Kerstin Johannesson, professor of marine ecology at the University of Gothenburg.
Today, sturgeon and herring are managed within the EU as four groups, so-called stocks, in the areas: the Gulf of Bothnia, the Baltic Sea proper, the Gulf of Riga and the western Baltic Sea. This is despite the fact that the stream in these areas can be divided into sub-stocks depending on whether they spawn in spring or autumn.
Local streaming can be wiped out
Research also shows that local stream groups have unique genes that have evolved over thousands of years to withstand different local temperatures and salinities in the Baltic Sea.
– If a local stock is wiped out, it is not certain that other herring will swim there instead, but the others will stay in their areas to which they have adapted and then there will be no herring there, says Kerstin Johannesson.
Collapse risks repeating
The Norwegian spring spawning stock of herring was fished to collapse in the 60s. Despite the fact that fishing was then stopped for 30 years, the herring has still not recovered and production is today much lower than before the herring was overfished.
– It can take a very long time before the partial stocks recover. It is unwise to push fishing this far, says Henrik Svedäng, fish researcher at Stockholm University.
Uncertainty requires lower quotas
Researchers at Uppsala University have developed a genetic analysis method that should make it easier to distinguish local sub-populations of herring. But the method is new and not yet available to fishermen.
– The only solution today is to go to a significantly lower level, says Henrik Svedäng.
– We risk standing there with a few stocks left that may not be particularly climate-adapted or capable of coping with future climates, says Kerstin Johannesson.