Photo by Adrian Kirby

The total biomass of fish stocks in Norwegian marine areas has nearly halved since 2013, falling to the lowest level recorded in the Institute of Marine Research’s time series, according to the latest Resource Overview presented in Tromsø. The Institute of Marine Research (IMR) estimates that the combined biomass of assessed fish stocks stood at around 35 million tonnes in 2013, with this figure dropping to approximately 17 million tonnes by 2025.

“2013 was a peak year. Since then, the total biomass in the sea, meaning the sum of all fish stocks where biomass data are available, has declined,” said Geir Huse, Research Director at the Institute of Marine Research. “This is the lowest level we have measured across the entire time series.”

Widespread recruitment failures drive decline

The Resource Overview assesses 46 fish stocks and concludes that the biomass decline reflects widespread difficulties rather than the collapse of a single stock. IMR reports weakened recruitment across several of the most commercially important stocks, a trend that has also been reflected in increasingly restrictive quota advice in recent years. Recruitment refers to the number of young fish surviving to join the adult stock.

For northeast Arctic cod, also known as skrei, the spawning stock has declined steadily since its 2013 peak and is now assessed to be between the precautionary reference level and the critical limit. “This is primarily due to failure in recruitment, meaning not enough young fish are growing up,” Huse said. “But in recent years, more skrei has also been fished than recommended.” The skrei quota agreed by Norway and Russia in December is the lowest since 1991.

Mackerel in critical state

Pelagic stocks have also declined sharply since 2000, with mackerel now described by IMR as being in a critical state. “For mackerel, the situation is now critical,” Huse stated. The spawning stock biomass has fallen from nearly 13 million tonnes in 2014 to around 2.7 million tonnes in 2025. IMR warns that once the spawning stock drops below three million tonnes, the stock’s ability to produce strong year classes is significantly reduced. “Recruitment over the past ten years has been weak, and fishing pressure in recent years has been too high.”

The Resource Overview assesses the status of six commercially key stocks, including blue whiting, mackerel, Norwegian spring-spawning herring, northeast Arctic haddock, cod and saithe, based on recruitment, biomass and fishing pressure. Several of these stocks are now classified as being in moderate or poor condition.

Climate and plankton link under investigation

Reduced plankton availability is likely contributing to poor recruitment across multiple stocks, strengthening the link between climate conditions and declining biological productivity. In response, the Institute of Marine Research is establishing a new research project to examine how plankton communities respond to climate change and what this may mean for future fish production and management decisions.