Herring Reproduction Biology

Schematische Darstellung des Lebenszyklus von Heringen, von der Eiablage über den Schlupf und die Larvenentwicklung bis zum Heranwachsen zum erwachsenen Tier und erneuter Eiablage. — Scheme of the life cycle of herring in the Western Baltic Sea.

Monitoring of larval herring abundance provides a reliable forecast for future population dynamics. But what causes strong or weak year classes? We possess an ecologically unique data set to investigate mechanisms structuring early life stage mortality.

Besides cod, Western Baltic herring is the major target species for the commercial fishery in the region. During the springtime, large schools of this stock leave the feeding- and overwintering areas and migrate towards their spawning grounds in the Western Baltic Sea. Shallow inshore systems, such as Greifswald bay (German: Bodden) are the major spawning areas of the stock. In these brackish systems, aquatic vegetation is an important substrate for adhesive, benthic herring eggs and the sheltered lagoon, rich in planktonic food, is a perfect nursery area for larval herring. To date we have collected a time series including more than three decades of spatially and temporally high resolution and ecologically unique data providing knowledge on the strong relation among reproduction success and stock dynamics. The monitoring data on larval production in Greifswald Bay provided by the “Rügen Herring Larvae Survey” (RHLS) is nowadays established in the ICES stock assessment procedure.

On the one hand, the aim of our herring recruitment research is to provide a solid, scientifically sound data base for a sustainable resource management. On the other hand, we aim to understand the ecological mechanisms determining successful reproduction and eventual year class strength. The basin scale of Greifswald Bay, the significant importance of the area for the entire population, the extensive time series and our analytical research are an outstanding platform to translate findings from ecological studies directly into sophisticated resource management.

Research on herring

Stark vergrößerte Heringslarven unterschiedlicher Entwicklungsstadien.

N20 recruitment index

The herring larvae that grow in the Greifswald Bodden in spring are a reliable indicator of the amount of offspring that can be fished in the western Baltic Sea in the future.

Unterwasseraufnahme von Heringseiern angeheftet an Seegras aus dem Greifswalder Bodden. Die Fischembryonen haben bereits deutlich entwickelte Augen.

Spawning habitats and egg development

Spawning and egg development are the first, important bottleneck in offspring production: above all, the availability of aquatic plants is important.

Grafische Darstellung der modellierten Verteilung von Heringslarven unter realen Windbedingungen. Nur ein sehr kleiner Teil der Larven wird in die freie Ostsee verdriftet.

Physical environment and larval retention

The Greifswalder Bodden is an important herring nursery because water temperature and oxygen supply are usually favourable here, and because the prevailing currents keep the hatched larvae in the area for a long time.

Unterwasseraufnahme von Stichlingen, die Heringseier von künstlich belaichten Strukturen abfressen.

Feeding ecology of herring larvae

The supply of food for herring larvae (bottom-up) and the appetite of predators for herring eggs and larvae (top-down) are important biological factors that influence growth and survival.