He less the western spring spawning Baltic herring than expected, but again one that lays its eggs in the fall. The new method provides researchers with detailed knowledge about various populations.

Atlantic herring is a keystone species in the North Atlantic; it plays an important role in the ecosystem and is dinner for many people.

Also for us humans: Fishing for Atlantic herring is one of the largest fisheries in the world.

Important – but also vulnerable

Herring swims coordinatedly in large shoals. This makes the species vulnerable to overfishing. Many tons of herring can be caught in one catch during fishing.

In the past, some herring populations have collapsed due to overfishing.

Therefore, good fisheries management is very important.

One species, many populations

But is herring only herring? Not. Herring is a species, but there are several “varieties,” different populations that live a little differently from one another.

Some lay their eggs in spring, some in autumn and some in winter.

Knowing “who belongs where” and what differentiates different populations is useful knowledge for better managing herring.

This is where HI researcher Florian Berg and his colleagues emerge.

– Genome sequencing allows to analyze and compare several million fish markers. Each fish has a unique genome, but among populations some markers are always the same. This gives us an opportunity to separate populations from one another, explains Berg.

Also read: Genome sequencing could lead to more sustainable herring fisheries

Genome sequencing provides new answers

Together with good colleagues from Denmark, Germany and Sweden, he has developed a new analytical method that makes it possible to investigate which populations of individuals differ – based on genome sequencing.

To test the method, the researchers examined catches from the North Sea, Norwegian Sea and Baltic Sea.

– We analyzed 3,734 herrings, brought from different spawning areas, where we found that herring populations did not mix. In addition, we analyzed data from grazing areas where populations were mixed. We have this data from trips in the period from 2002 to 2021.

– Now we have a new and better picture of the various Atlantic herring populations and how they mix, said HI researcher.

There are more autumn spawners in the Baltic Sea than expected

One population of concern is the herring which spawns in spring in the western Baltic Sea.

In this study, the researchers noticed that stock sizes had been overstated – so the situation was even worse than originally thought.

The good news is that researchers have discovered that the fall-spawning herring in the western Baltic Sea – which is genetically distinct from the spring-spawning herring – is a larger and more important population than previously thought.

– Autumn spawning herring is thought to be of little significance to the fishery, but we see that it makes a significant contribution to mixed stocks. It may also increase in the future, due to climate change, said Berg.

– These findings suggest that we may have to reevaluate how we define different stocks from one another.

Can be used to rebuild stock

What can special knowledge of herring populations be used for? Yes, precisely to improve herring monitoring, so that overfishing can be avoided. Or, after the disaster is over, to rebuild supplies.

– When we know how different populations mix, how they live and what are the differences between them, we can introduce more targeted measures to protect vulnerable populations, explained the HI researcher.

– We currently use a fixed boundary, say 62 degrees north, to separate stocks from one another. With this methodology, we may eventually be able to move to a more flexible frontier, where we follow the migration patterns of different populations.

Going forward, researchers will continue to work to map various herring populations along the Norwegian coast.

Reference

Dorte Bekkevold, Florian Berg, Patrick Polte, Valerio Bartolino, Henn Ojaveer, Henrik Mosegaard, Edward D Farrell, Jelena Fedotova, Jakob Hemmer-Hansen, Bastian Huwer, Vanessa Trijoulet, Christoffer Moesgaard Albertsen, Angela P Fuentes-Pardo, Tomas Gröhsler, Mats Pettersson, Teunis Jansen, Arild Folkvord, Leif Andersson, Mixed stock analysis of Atlantic herring (Clupea harengus): a tool for identifying management units and complex migratory dynamics, ICES Journal of Marine Science, 2023;, fsac223

Link: https://doi.org/10.1093/icesjms/fsac223