The skrei is on its way

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Photo: Erling Svensen / Havforskingsinstituttet

Right now, millions of northeast arctic cod (skrei) are migrating from the Barents sea to the Norwegian coast to spawn. They are the lucky few survivors.

Catches are increasing in northern Norway, as is usual for this time of year.

The researchers estimate that the total amount of skrei will be somewhat smaller than in 2019, but still high historically.

Spawning happens underway

The skrei spawn along the coast from Finnmark in the North to Western Norway. The spawning is an act of coreography with strict rules for courtship. The fish swim with their undersides against each other for a few seconds while releasing eggs and sperm.

"Each female can produce between half a million and 15 million eggs, depending on age and size," says researcher Bjarte Bogstad.

Develops quickly

If the spawning is a success, the egg develops from one to many cells in hours. After a while the lump of cells begin to take shape. After mere days, it is an embryo with eyes.

It becomes clear that there is a fish larvae inside the egg.

How long the process takes, depends on sea temperature. When the temperature is around 5 degrees, the larvae hatches after 20 days. An enzym will weaken the eggshell.

Very few survive

The newly hatched larvae have to find food while avoiding being eating by larger fish, krill or jellyfish. Few do.

"Fewer than one egg per million grow into fish that get to spawn during their lifespan."

Embryo stage of a skrei. (Photo: Anders Thorsen / Institute of Marine Research)