Spawning areas

Baltic Herring Spawning Behavior

Baltic herring reproduces mainly in spring. However, the spawning period can vary across both time and space. In the southern Baltic Sea, spawning begins in late February and extends to early May. Meanwhile, in the Archipelago Sea, spawning starts in early May and can last until July or even August. As individual fish release their gametes at one time, long spawning period is most likely a consequence of different maturation rates of fish in the herring stock.

Where Spawning Occurs

Herring spawn along the Baltic Sea’s coastal zone, from the eastern side of the Danish sounds to the northern parts of the Bothnian Bay. Notable spawning grounds include the Greifswalder Bodden, the Gulf of Riga, the Stockholm Archipelago, and the Archipelago Sea in southwestern Finland (see map).

Major spawning areas of the herring in the southern, central and northern Baltic Sea. AS=Archipelago Sea; SA=Stockholm Archipelago; GOR=Gulf of Riga; GB= Greifswalder Bodden, B=Bothnian Bay. Map on the right: Airisto inlet in the Archipelago Sea; blue circles indicate monitored spawning beds.
Major spawning areas of the herring in the southern, central and northern Baltic Sea. AS=Archipelago Sea; SA=Stockholm Archipelago; GOR=Gulf of Riga; GB= Greifswalder Bodden, B=Bothnian Bay. Map on the right: Airisto inlet in the Archipelago Sea; blue circles indicate monitored spawning beds.

Spawning Conditions

Herring typically spawn in shallow waters (0-10 meters) among aquatic vegetation. They aren’t picky about their spawning substrate, as eggs can be found on various underwater plants and algae. However, the presence of vegetation is crucial for spawning, among other environmental factors. Herring eggs attach to aquatic plants and remain there until they hatch.

Challenges in Spawning Grounds

Unfortunately, the presence of underwater vegetation in the Baltic Sea’s coastal areas has decreased due to reduced underwater light caused by eutrophication and high particle load. As light diminishes, submersed vegetation dies or relocates to shallower waters where there’s still enough light. If important nursery areas are affected by human-induced habitat degradation and environmental conditions of important nurseries become unfavorable for successful herring reproduction, but herring continue their migrations to these specific anthropogenic-stressed habitats, this might have severe impacts for the population persistence. This shrinking of suitable spawning areas affects herring recruitment and stock size negatively over time.

Our research, spanning back to the 1980s in the Airisto Inlet, challenges the notion that Baltic herring spawn anywhere with suitable conditions. Instead, herring are selective, choosing specific locations year after year. While we don’t fully understand the reasons behind this selectivity, it’s a common behavior among herring and other fish species.

Over evolutionary time, herring have developed this selective spawning behavior due to its advantages for reproductive success. However, in the modern Baltic Sea, traditional spawning grounds are less favorable. Herring now spawn in areas with less-than-optimal conditions. For instance, in the Airisto Inlet, high egg mortality is observed due to increased eutrophication, sediment load, and pollutants.

A recent concern is the detachment of eggs from their spawning substrate before hatching, observed in SCUBA diving surveys. Eggs disconnect, stop developing, and are carried away by waves and currents. This poses a significant threat to herring reproduction.

Related Publications

  • Vahteri, P. & Vuorinen, I. 2001. The crash in Baltic herring (Clupea harengus membras L.) reproduction – a case study in the northern Airisto spawning grounds, Archipelago Sea S-W Finland. Baltic Sea Science Congress 2001, Abstract Volume. Stockholm University, Stockholm, Sweden.
  • Griffin, F.J., Pillai, M. C., Vines, C. A., Kääriä, J., Hibbard-Robbins, T., Yanagimachi, R. & Cherr, G. N. 1998. Effects of salinity on sperm motility, fertilization, and development in the Pacific herring, Clupea pallasi. Biol. Bull. 194: 25-35.
  • Kääriä, J., Rajasilta, M., Kurkilahti, M. & Soikkeli, M. 1997. Spawning bed selection by the Baltic herring (Clupea harengus membras) in the Archipelago Sea of SW Finland. – ICES J. mar. Sci. 54: 917-923.
  • Rajasilta, M., Eklund, J. Hänninen, J., Kurkilahti, M., Kääriä, J. Rannikko, P. & Soikkeli, M. 1993. Spawning of herring (Clupea harengus membras L.) in the Archipelago Sea. – ICES J. mar. Sci. 50: 233-246.
  • Rajasilta, M., Eklund, J., Kääriä, J. & Ranta-aho, K. 1989. The deposition and mortality of the eggs of the Baltic herring, Clupea harengus membras L., on different substrates in the south-west archipelago of Finland. – J. Fish. Biol. 34: 417-427.
  • Rajasilta, M., Eklund, J., Kääriä, J. & Ranta-aho, K. 1989. The deposition and mortality of the eggs of the Baltic herring, Clupea harengus membras L., on different substrates in the south-west archipelago of Finland. – J. Fish. Biol. 34: 417-427.