New survey seeks coastal herring missing from stock estimates

Natural Resources Institute Finland has begun a pilot study of shallow coastal waters to determine how many herring they contain, Yle reports. The results could affect future fishing quotas.

The institute has carried out acoustic surveys and research trawling this week along the southeastern coast of the Bothnian Sea. Researchers suspect that large numbers of young herring live in shallow coastal waters that have not been reached by the Finnish Environment Institute’s larger research vessel Aranda, lead researcher Jari Raitaniemi said.

Aranda mainly operates in waters deeper than 40 metres. Researchers have sometimes only detected a new year class once the herring have reached two to four years of age.

During the first night of acoustic surveying, large numbers of fish were found at a depth of 20 metres. The area could not be trawled because of its uneven seabed. A trawler operating slightly deeper caught herring, sprat and smelt.

Raitaniemi said that supplementing Aranda’s research trips with smaller boats operating closer to shore could provide a more accurate picture of the herring stock.

Results could affect the 2028 quota

Stock estimates help determine how much herring can be caught. Fishers have criticised the quota, arguing that it may be based on an estimate that is too low.

The new study’s results could affect the quota for 2028 at the earliest, Raitaniemi said. Natural Resources Institute Finland will survey shallow waters for the rest of this week. Aranda will then spend two weeks in the central Bothnian Sea, south of the Åland Islands and in the Gulf of Finland.

Once the results from both trips are available, researchers can make a preliminary estimate of the size of the year class, Raitaniemi said. The age analysis of the herring being studied is expected to be completed in late winter or early spring.

The first stock estimate will be discussed at a meeting on Baltic Sea fish stocks in April. The assessment will then move to the International Council for the Exploration of the Sea and finally to its advisory committee. The council is expected to publish its advice on a possible 2028 quota around the turn of May and June.

Large fluctuations in herring numbers

Stock assessments also take into account observations from previous years, and those observations have varied greatly in recent years.

Herring in the Bothnian Sea suffered from starvation in 2021 and 2022. Many fish were thin, while larger herring died and largely disappeared from the sea, Raitaniemi said.

Researchers feared at the time that the herring stock had collapsed, but it began to recover. Acoustic observations have since repeatedly risen and fallen, possibly because young fish that prefer coastal waters have not been detected by the surveys.