Finland studies Baltic herring in the shallow waters of the Bothnian Sea — YLE News
The Natural Resources Institute Finland has launched a pilot study of Baltic herring abundance on the southeastern coast of the Bothnian Sea. Scientists are conducting echo-sounding surveys and research trawls to account for fish that may live in shallow coastal waters.
As YLE News reports, the large research vessel Aranda operates mainly at depths of more than 40 metres. According to lead scientist Jari Raitaniemi, this means young Baltic herring that may stay in shallow coastal waters could have been missed in previous stock assessments. During the first night of echo sounding, a large number of fish were detected at a depth of 20 metres, but trawling there was not possible because of the uneven seabed.
Shallow-water study
The research vessel Aurelia, which can conduct echo sounding in shallow waters, is being used to survey coastal areas. At a somewhat greater depth, the trawler caught Baltic herring, sprat and smelt. Raitaniemi believes that combining data from Aranda expeditions with nearshore research using smaller vessels will make it possible to assess the actual state of the Baltic herring stock more accurately.
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Impact on the 2028 quota
The stock assessment affects, among other things, the volume of permitted Baltic herring catches. Fishers had criticised the quotas because they suspected they might be based on an underestimated fish abundance. According to Raitaniemi, the results of the current study may affect the quota no earlier than 2028.
The survey of shallow-water areas will continue this week. After that, Aranda will set out on a two-week expedition to the central part of the Bothnian Sea, south of the Åland Islands and to the Gulf of Finland. The age determination of the Baltic herring being studied is expected to be completed at the end of winter, and the first stock assessment will be considered at a Baltic Sea fish stock assessment meeting in April.
In 2021–2022, Baltic herring in the Bothnian Sea were starving: there were many thin fish, while large individuals died and largely disappeared from the area. The stock later began to recover, but echo-sounding observations during the current decade have fluctuated significantly. The researcher named the fact that young fish staying near the coast were not recorded during previous surveys as one possible reason for these changes.
