Stock of young herring in the Barents Sea (Clupea harengus)

Herring
Photo: Institute of Marine Research

In recent years, the herring stocks has declined, but now seems to have stabilized. To prevent further decline, we depend on good fish management and use of the precautionary principle.

What is being monitored?

Biomass of young herring in the Barents Sea

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The graph shows the distribution between the year classes of juvenile herring in the Barents Sea shown as biomass index. In 2018 the herring index was not calculated due to lack of coverage.

Status and trend

The last large year class of young herring in the Barents Sea was in 2004. These have now migrated, and the last years, there has been little young herring left in the Barents Sea. In 2013 however, relatively many zero- year olds were observed. This year class has mostly left the Barents Sea by now. In 20178, a lot of 1-year olds were observed, and the biomass index for the 2016-year class was the highest since the year class of 2004 was measured as 1-year olds in 2005. High biomass index for the 2016 year class was further confirmed in 2019,- now as a relatively high estimate of 3-year olds. Due to lack of coverage, no herring index was calculated for 2018.

The quantity of young herring is mainly connected with factors like the population size of the spawning stock, and physiological as ecological conditions in the Norwegian Sea. Conditions in the Barents Sea will significantly influence the growth and mortality of the individual year class.

A large quantity of young herring in the Barents Sea is an important ecological factor. The herring in the Barents Sea prey on capelin larvae, and the growth of the capelin stock is poorer when there is a strong stock of young herring in the Barents Sea.

Capelin is considered a keystone species significantly affecting the ecosystems. Herring is therefore also a key ecosystem player, even if it only stays in the Barents Sea when young and migrate before maturation.

The amount of young herring can also affect cod. Cod eat herring, but stomach samples shows that herring only partially replaces capelin as food for cod. When large quantities of juvenile herring are present in the Barents Sea, growth of the cod stock in the Barents Sea will therefore be reduced.

Causal factors

Young herring in the Barents Sea are affected by many factors such as the sea temperature, the availability of food and the occurrence of capelin and cod.

The herring fishery mainly takes place outside of the Barents Sea. The young herring in the Barents Sea are protected by international agreements and are harvested to a very limited extent.

The Norwegian spring-spawning herring stock suffered a collapse around 1970 due to heavy overfishing. In 1972, the spawning stock was so low that only two herring larvae were found during the annual larvae estimation cruise along the entire Norwegian coast.

Consequences

Recruitment to the herring stock will vary greatly from year to year. In recent years there has been little young herring in the Barents Sea. It seems like the 2013 year class, of which was measured relatively many of as zero-olds, has mostly left the Barents Sea. However, it looks like the 2016-year class is numerous and may affect the ecosystem in the Barents Sea the following years.

About the monitoring

The indicator describes the amount of herring that are 1-3 years old, and how this change over time. The amount of herring from this age group is considered as a good starting point for assessing the amount of immature herring in the Barents Sea.

 

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring