Herring and sprat: silver of the sea that turned into sand
8 December 2021
COLUMN. “I’m passionate about understanding the genetic background of biodiversity development and I’d like our research to culminate in more sustainable use of herring and sprat, which are a superb resource,” writes Leif Andersson, Professor of Functional Genomics.
Herring is a well-known item on the Swedish Christmas table that will be appearing this month. Sprat, which Swedes call ansjovis (not the same as the European or Mediterranean anchovy, but rather filleted sprat), closely related to herring but smaller, is a major ingredient in the seasonal dish known as “Jansson’s Temptation”. For millennia, the herring supply has been crucial for food security in Sweden, which would not be the country it is today without the abundance of Atlantic and Baltic herring throughout the period when food imports were very limited.
Today, approximately 100,000 tonnes of herring and some 50,000 tonnes of sprat are fished annually in Sweden. About 75 per cent of this catch is sold, for SEK 2 per kilo, for fishmeal production. The silver of the sea has turned to sand. At a time when we are doing all we can to find more climate-smart foods, this is an anomaly we need to address. Herring and sprat contain high-quality protein and omega-3 fatty acids, a human food resource that deserves a better fate than to become fishmeal.
The research we conduct on herring and sprat has both provided exciting new knowledge about how species adapt to their environment and resulted in new methods for developing more sustainable uses of this excellent resource. Our research has shown that the huge quantities of herring in the Atlantic and the Baltic Sea can be divided into many local stocks displaying very clear genetic adaptation to their environment. For example, a couple of hundred genes distinguish our Baltic herring (strömming) from the Atlantic herring (sill).
In sharp contrast is the European eel, which forms a single, genetically undifferentiated eel population that is panmictic (not subject to any interbreeding restrictions). We believe that the explanation for the difference is that the herring populations spawn under very different environmental conditions (temperature, salinity and light, for example), while the whole European eel population reproduces under near-identical conditions in the Sargasso Sea. Spawning and early development are the most vulnerable phases of the fish life cycle.
Our research can contribute to more sustainable exploitation of herring and sprat in two ways. We have identified thousands of genetic markers that can be used to monitor local stocks and help to ensure that they do not collapse owing to overfishing. We also aim to identify fish stocks with low concentrations of environmental pollutants (notably dioxin) that are much more suitable for human food than for fishmeal production. My hope is that in the years ahead we will see greater use of herring and sprat in cooking, and not just as delicacies on the Christmas table.
Leif Andersson, Professor of Functional Genomics at the Department of Medical Biochemistry and Microbiology