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 stock of young capelin has stabilized over the last years.

Status and trend

The last large year class of young herring in the Barents Sea was in 2004, and the last years, there has been little young herring left in the Barents Sea. In 2018, a lot of 1-year olds were observed, and the biomass index was the highest since the year class of 2004 was measured as 1-year olds in 2005.

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

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

In recent years there has been little juvenile herring in the Barents Sea. In 2013 there were observed relatively much zero-old herring in the Barents Sea. This year class is for the most part out of the Barents Sea. In 2017, a lot of 1-year olds were observed in the Barents Sea, and the year class of 2016 seems to be the most numerous since the year class of 2004.

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 it was measured relatively many of as zero-olds, is mostly out of 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 changes 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.

The time series going back to 1973. The Institure of Marine Reseach (www.imr.no) is responsible for monitoring the herring stock.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring