Discover our other sites:

You might be looking for...

THIS CONTENT IS BROUGHT TO YOU BY THE University of Agder - read more

Coastal cod struggle in hot summers

Rising sea temperatures make it increasingly difficult for young cod along the Skagerrak coast to survive.

Small cod swimming in an aquarium among blurred plants and a blue background.

Cod are being squeezed between warmer seas and heavy fishing pressure, leaving little room for the stock to recover.

(Photo: Espen Bierud / Institute of Marine Research)

Sissel Eikeland Sissel Eikeland COMMUNICATIONS ADVISER

Presented by: Presented by: University of Agder

Published 8 July 2026 - 00:01

Right now, young cod are swimming along the Skagerrak coast. They are up to five centimetres long, live in shallow water, and have few places to hide if the summer becomes warm.

Researcher Marte Sodeland at the University of Agder's Department of Natural Sciences is concerned.

“Last year, survival rates for cod were low. And now it looks like we’re heading for another warm year. That's bad news for several important species in the Skagerrak,” she says.

Sodeland studies the genetic material of fish and other species along the coast. Among other things, she tries to understand how resilient species are in the face of climate change and how they are affected by human activity.

Portrait photo — Marte Sodeland is an evolutionary geneticist who studies the genetic material of fish and other coastal species.

She is concerned because the seasonal forecast from the Norwegian Meteorological Institute states that there is a 70 per cent chance of a warmer-than-normal summer in Eastern Norway and Agder.

“Cod spawn from January to April. After the eggs hatch, the young fish have now settled on the seabed close to shore. Coastal cod spend their first summer in shallow water. Unfortunately, this water becomes too warm in summer,” she says.

Sodeland explains that juvenile cod begin to struggle when temperatures stay above 18 degrees.

“Along the Skagerrak coast, surface temperatures now regularly exceed this,” she says.

Two types of cod with different fates

There are two types of cod along the Skagerrak coast.

Fjord cod, also called coastal cod, are the local, resident cod that stay in the area throughout their lives. North Sea cod migrate farther out into the open ocean.

Fjord cod are the fish that recreational fishers mainly catch along the coast and in the fjords.

“During their first summer, both North Sea cod and fjord cod do best in water of around 16 degrees. When summer temperatures remain above this, they start to struggle,” Sodeland says.

A recent report from the Institute of Marine Research documents a dramatic decline in the stock along the entire Skagerrak coast.

From 2006 to 2024, cod numbers fell by 75–80 per cent.

In eastern Skagerrak, from the Oslofjord down towards Agder, the decline has been ongoing since the 1990s and is now at an extremely low level.

The situation is spreading westward

Conditions are worst from the Oslofjord down along the coast. But researchers describe a clear pattern.

“What we see is that the Skagerrak coast from the Oslofjord to Lindesnes is in worse condition than the stretch from Lindesnes westward. It's worst in the east, but the problem is increasingly spreading southwards along the Skagerrak,” Sodeland says.

Warm summers make it harder to reverse the trend. And according to Sodeland, the coming years could be critical. Forecasts suggest that 2027 may also be a warm year.

“When we get three such extreme years in a row, and we know that cod do not live very long because we fish them heavily, then it's serious,” she says.

A vulnerable gene pool

Sodeland is an evolutionary geneticist and views the decline primarily from that perspective.

According to her, cod need a large and diverse gene pool to cope with a changing climate. This means there must be many cod, ensuring rich and varied genetic material. Some individuals survive cold years, while others survive warm ones.

“The greater the diversity, the more robust the fjord cod population becomes,” she says.

The problem is that fishing pressure and warm summers are occurring simultaneously.

“When we fish so heavily, the gene pool shrinks. The population becomes less flexible and less able to cope with climate change than it could have been if we gave it more room,” she says.

Measures in the Oslofjord are not enough

From 1 January 2026, the Norwegian government introduced no-fishing zones in the Oslofjord. Sodeland does not believe this is sufficient on its own.

“It's as if we're just waiting for the situation to get worse here along the Skagerrak coast as well. Responsibility must be taken for the entire coast. We cannot just pat ourselves on the back for the measures in the Oslofjord,” she says.

“Measures in the Oslofjord are necessary, but not sufficient on their own. We need measures that also apply to the Skagerrak coast down towards Lindesnes,” she adds.

Recreational fishing is barely regulated

While salmon fishing in rivers is strictly regulated, with registration requirements and limited quotas, recreational cod fishing along the coast is in practice largely unrestricted.

There is a minimum size of 40 centimetres, but there are no catch quotas, no registration requirement, and no reporting. Tourist fishing is just as poorly regulated.

According to a report from the Institute of Marine Research, recreational fishing along the coast is actually three times more lethal for coastal cod than commercial fishing is for North Sea cod.

“I don't want to point fingers. I have children myself who love fishing. But even though there's not sufficient regulation in place, it might help if we all think a little before deliberately targeting this vulnerable species,” Sodeland says. “And if you catch cod, release it again regardless of its size."

References:

Chung et al. First measurements of field metabolic rate in wild juvenile fishes show strong thermal sensitivity but variations between sympatric ecotypes (Abstract), Oikos, 2021. DOI: 10.1111/oik.07647

Sodeland et al. “Islands of Divergence” in the Atlantic Cod Genome Represent Polymorphic Chromosomal Rearrangements, Genome Biology and Evolution, 2016. DOI: 10.1093/gbe/evw057

Sodeland et al. Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation, PNAS, 2022. DOI: 10.1073/pnas.2114904119

Stock et al. Oppdatert status om torsk langs Vestlandet- og Skagerrakkysten: potensial for bestandsvurdering (Abstract in English), Report from the Institute of Marine Research, 2025.