Scientists have made an unexpected discovery – a new species of Baltic herring. It is called predatory herring because, unlike ordinary herring, it feeds on small fish instead of plankton. According to Leif Andersson, a geneticist at Uppsala University and one of the researchers behind the study, the discovery could have major implications for the management of Baltic herring.
Along some parts of the Baltic coast, an unusually large type of Baltic herring, known as slåttersill, has existed since ancient times. But why these herrings grow faster than ordinary herring has long been a mystery. Now, new research from Uppsala University and the Swedish University of Agricultural Sciences, partly funded by BalticWaters, shows that the herring is a genetically unique variant of Baltic herring.
– The new variant is piscivorous, meaning that it eats small fish. This makes it grow faster and larger than ordinary herring, says Leif Andersson, who has long been researching the genetics of herring.
The new discovery, together with previous genetic research from Leif’s research group, sheds light on the great diversity of herring, and at the same time reveals the previously unknown role of predatory herring as a predatory fish in the Baltic Sea ecosystem.
The researchers found that one fish was a particularly common food for the predatory Baltic herring – the three-spined stickleback – a fish species that has increased dramatically in recent decades, with major effects on coastal ecosystems.
– The stickleback population has increased in the Baltic Sea, probably as a result of the decline of predatory fish, such as cod. Stickleback eat the eggs and larvae of predatory fish, creating a vicious circle where predatory fish populations continue to decline, Leif explains.
Predatory herring can therefore play an important role in keeping the stickleback in check, which Leif believes would contribute to greater stability in the ecosystem. But it is not enough to rely solely on this new predatory fish. During his work, Leif has spoken to many fishermen from the Uppland coast, whose unanimous view is that predatory herring have also declined in numbers.
The most reasonable interpretation is that large-scale fishing for herring is behind the change, he says.
The size difference between the predatory slåttersill (at the bottom) and ordinary autumn and spring spawning herring (at the top). Photo: Leif Andersson
It is clear that predatory Baltic herring are an important component of the Baltic Sea ecosystem. But what does this discovery mean for the management of Baltic herring?
– We have a common understanding that it is important to preserve genetic diversity, but fisheries management has not kept up with the science. At present, all Baltic herring are subject to the same quota, which is problematic, Leif points out.
He therefore argues that fisheries management must change to take into account the genetic diversity of Baltic herring.
– Management of Baltic herring must recognise the significant genetic diversity of this species to ensure that unique stocks like the Baltic herring are not lost.
To conserve herring, Leif highlights one particularly important measure – strengthening protection in coastal areas, where herring are most likely to hunt small fish.
– Moving the trawl limit for large-scale herring fishing could thus be a measure to protect this unique herring population, the herring’s diversity, and ultimately contribute to increased stability in the Baltic Sea ecosystem, Leif concludes.
Want to know more about predatory herring?
The scientific article is available in Nature Communications, read it here.
Leif Andersson also appeared on Swedish Radio to talk about the discovery, listen to the programme here (in Swedish).
Secrets of the Baltic herring will be decoded at BalticWaters fish laboratory
Despite advances in research, there are still many mysteries surrounding the genes of Baltic herring. But scientists are determined to solve them. In 2025, a research team led by Leif Andersson will begin a new project to investigate which genes are responsible for the herring’s ability to adapt to its environment.
The project will be carried out at BalticWater’s new fish research laboratory and is expected to provide invaluable knowledge about the Baltic herring’s capacity to cope with climate change, while contributing to more sustainable fisheries management.
