Key findings
A decade without strong year classes (2005-2015) led to a decline of about 40% in the spawning-stock biomass of Norwegian spring-spawning herring, from about 7 to about 4 million tonnes. Since then the stock has been about 2.5-4.5 million tonnes.
Since 1994 the total catch of all nations has been 0.3-1.7 million tonnes per year and the Icelandic catch 21-265 thousand tonnes per year. In recent years >90% of the Icelandic catch has been taken within the Icelandic EEZ, and in 2025 >95% off the East Fjords.
The catch in recent years has been dominated by the strong 2016 year class, which made up about 45% of the catch in 2025. Mean weight at age decreased for all age groups in 2008-2012 but generally increased after 2018, with older age groups at or above the long-term average and younger herring close to or slightly below average.
The 2021 and 2022 year classes, which are recruiting to the fishable stock, are estimated to be above average.
The strong 2016 year class shifted spawning along the west coast of Norway further north than before, towards Lofoten, and the feeding season has become longer; the stock stays longer off the east coast of Iceland into the autumn.
General information
Norwegian spring-spawning herring (Clupea harengus) is a highly migratory and widely distributed pelagic fish. The Norwegian spring-spawning herring stock is the largest herring stock in the world and undertakes longer feeding migrations than other herring stocks (Dragesund et al., 1997). The herring spawns along the west coast of Norway in February and March. Large fluctuations have been observed in the north-south distribution of the spawning grounds over the centuries (Devold, 1963; Dragesund et al., 1997; Slotte et al., 2025). The most recent changes are linked to the strong 2016 year class, which has moved spawning north towards Lofoten (Slotte et al., 2025). After spawning, the herring migrates to feed in the Norwegian Sea and adjacent waters, including east and north of Iceland (Libungan, 2021). The feeding migrations are linked to seasonal variation in the abundance and distribution of zooplankton, as well as competition for food with other pelagic species (e.g. mackerel and, to some extent, blue whiting; Pavshtiks, 1956; Óskarsson et al., 2016). The feeding migration begins in April and intensifies in May and June, when an important part of the diet, Calanus finmarchicus, moves from deeper layers to the surface layers after overwintering (Pétursdóttir et al., 2012). In recent years the feeding period has extended further into the autumn and the stock has stayed longer off the east coast of Iceland (Homrum et al., 2022).
Both the extensive feeding areas of mature herring and its main nursery area in the Barents Sea are likely reasons for the high productivity and size of the stock (Trenkel et al., 2014). The stock is characterised by irregular production of strong year classes, and long gaps between them can have severe consequences for the stock (Toresen & Østvedt, 2000). For example, no strong year class recruited to the stock in 2005-2015, which led to a 40% decline in spawning-stock biomass, from 7 million tonnes to 4 million tonnes (Tiedemann et al., 2020).
Data used in the assessment of Norwegian spring-spawning herring come from annual acoustic surveys in the Norwegian Sea, which have been conducted since 1995 and in which Iceland has participated from the start. More about the Icelandic part of the survey can be found in the report published by the Marine and Freshwater Research Institute (in Icelandic). The survey data are important for the assessment of the stock, and also for evaluating variability in the environment and ecosystem of the ocean. Abundance indices by age, obtained from acoustic measurements and sampling of herring registrations, are important for tuning the stock assessment model (ICES, 2025).
Fishery and catch trends
Icelandic fishing for Norwegian spring-spawning herring started in the 19th century and expanded after 1930. In the years after the Second World War, particularly from 1940 to 1970, the fishery grew substantially and became important for the Icelandic fishing industry, with herring becoming one of the nation’s most important resources. The stock subsequently collapsed due to overfishing around 1968 and was not seen again in Icelandic waters until 1994, when Icelandic vessels caught 21 thousand tonnes. Since 1994 the annual total catch of all nations from the stock has ranged from 0.3 to 1.7 million tonnes (Figure 1).
Since the fishery resumed, the total Icelandic catch has ranged from 21 to 265 thousand tonnes (Figure 2). The fishing areas of Icelandic vessels have changed over time, and from around 2005 the proportion of the catch taken within the Icelandic EEZ increased. In recent years more than 90% of the Icelandic catch has been taken within the Icelandic EEZ (Figure 2).
In 2001-2005 the Icelandic fishery was in the north-eastern Norwegian Sea, between Jan Mayen and Svalbard; about half of the catch was taken in international waters and about a quarter in the Svalbard zone (Figure 3, Figure 4). From 2006 the fishery moved south-west, and in 2006-2010 just over 60% of the catch was taken within the Icelandic EEZ. In 2011-2015 about 80% of the catch was taken within the Icelandic EEZ and most of the rest in the Faroese EEZ. In 2016-2021 the fishery moved further into the area east of Iceland, and in 2025 >95% of the total catch was taken in a small area off the East Fjords.
Sampling
The age composition of the catch is estimated from samples of the catch of fishing vessels, collected at sea by fishers, together with catch information from the Directorate of Fisheries. Sampling of the catch was good in 2025 and covered the main distribution of the fishery (Figure 5). The number of samples, length measurements and age readings since 2004 is shown in Table 1.
| Year | No. of stations | No. of fish measured | No. of fish aged |
|---|---|---|---|
| 2004 | 8 | 150 | 148 |
| 2005 | 49 | 1829 | 1792 |
| 2006 | 31 | 1269 | 633 |
| 2007 | 90 | 6975 | 2994 |
| 2008 | 80 | 3664 | 3664 |
| 2009 | 162 | 9355 | 6258 |
| 2010 | 256 | 19621 | 7235 |
| 2011 | 184 | 9261 | 6236 |
| 2012 | 105 | 5448 | 2861 |
| 2013 | 96 | 4158 | 2793 |
| 2014 | 75 | 5221 | 1557 |
| 2015 | 43 | 1907 | 1539 |
| 2016 | 56 | 2441 | 1839 |
| 2017 | 82 | 3719 | 2116 |
| 2018 | 59 | 2822 | 1425 |
| 2019 | 89 | 4198 | 2299 |
| 2020 | 62 | 3327 | 1443 |
| 2021 | 89 | 5191 | 2101 |
| 2022 | 65 | 4214 | 1373 |
| 2023 | 93 | 6269 | 2123 |
| 2024 | 73 | 3261 | 2260 |
| 2025 | 72 | 3306 | 1955 |
Catch composition
The length distribution of Norwegian spring-spawning herring in the catch by year is shown in Figure 6. The annual mean length in the catch ranges from 31 cm to 35 cm. The size composition of the catch has changed over the years: from 2007 to 2019 larger herring were prominent in the catch, whereas since 2020 younger fish have been more prominent.
Catch at age
Catch in numbers at age is shown in Figure 7. From 2008 a large part of the landed catch was the 2002 year class, which dominated the catch until 2012. Older herring has been prominent in the Icelandic catch since the turn of the century, but in recent years the share of the 2016 year class has increased. In 2025 the 2016 year class made up just over 45% of the total catch (Figure 8).
Mean weight at age in the catch is shown in Figure 9. Mean weight at age decreased in 2008-2012, reaching a minimum for many age groups. Mean weights generally increased after 2018; for older fish, weights have remained at or above average since then, while younger age groups have been at or below average in recent years.
References
Devold, F. 1963. The life history of the Atlanto-Scandian herring. Rapports et Procès-Verbaux des Réunions du Conseil International pour l’Exploration de la Mer, 154: 98-108.
Dragesund, O., Johannessen, A. & Ulltang, Ø. 1997. Variation in migration and abundance of Norwegian spring spawning herring (Clupea harengus L.). Sarsia, 82: 97-105.
Homrum, E. í, Óskarsson, G.J., Ono, K., Hølleland, S. & Slotte, A. 2022. Changes towards stable good somatic condition and increased gonad investment of Norwegian spring-spawning herring (Clupea harengus) after 2005 are linked to extended feeding period. Frontiers in Marine Science, 9: 803171. doi:10.3389/fmars.2022.803171
ICES. 2025. International ecosystem survey in the Nordic Seas (IESNS) in April to May 2025. WD05 to the Working Group on International Pelagic Surveys (WGIPS) and the ICES Working Group on Widely Distributed Stocks (WGWIDE, No. 8). ICES, Copenhagen, Denmark (hybrid meeting), 27 August - 2 September 2025.
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