CURRENTLY LIMITED EFFECT OF COD ESCAPE IN VOLDSFJORDEN

The fjord has been monitored since 2022 when 87,000 farmed cod escaped from a fish farm in Voldsfjorden.  

Now the results are clear. 

“We have studied cod from the area over two winter seasons, in 2022/23 and 2023/24. In the latter, eggs were also collected during the spawning season. In total, we obtained samples from 392 cod and found 562 fish eggs that were the same size as cod eggs.” says marine scientist Terje van der Meeren.  

To determine whether the cod were escapees from the fish farms, and whether the eggs came from the same escapees, the researchers used DNA analyses. 

“In the winter of 2022/23, DNA analyses showed that we had collected 87 farmed cod and 95 wild cod. Most of the farmed cod this year were caught near the facility from which they had escaped.”

Waiting for the escapees to become sexually mature 

No egg surveys were conducted in the first year. 

“The fish that escaped only weighed 600 grams on average. We considered it unlikely that such a small cod was sexually mature, so egg examination was not necessary.” says the researcher. 

The following winter, 2023/24, the fishing effort for adult fish was somewhat lower.  

“A total of 50 cod were caught that we could determine the origin of, of which five were farmed fish.” 

This season, fish eggs were also collected to see if the escapees had managed to spawn. 

Only one egg from farmed cod was found 

Several fish species spawn at the same time as cod, and many of them have eggs of approximately the same size.  

“A total of 562 fish eggs of the correct size were collected. To identify the cod eggs, we used DNA analyses.” says van der Meeren.  

The results showed that 233 of the eggs were from cod, and only one of these strains was from farmed cod.

Compound cause hinders genetic influence 

“So far, it appears that there has not been a major genetic impact on the wild fish as a result of this escape.” says van der Meeren.  

The reason for this is compounded: 

“It may look as if there has been a high mortality rate among the escaped cod, and they may also have spread over a larger area than the one we examined.” 

He also points out that eggs spawned by escaped farmed cod have probably been spread out, making it difficult to find them in such a limited survey as the researchers conducted in this area.  

Genetic influence from farmed fish to wild fish only occurs if farmed cod spawn together with wild cod to some extent, then the offspring receive a mix of genes from both parents – and thus also “farmed genes”. 

Farmed cod can still “emerge” again 

In the case of the escape in Voldsfjorden, the researchers have several reservations about the results: 

“Escaped cod have been found more than a year after the escape, and we cannot rule out that escaped cod will “appear” both this year and later, and that these may spawn together with the wild fish.” he says.  

“When farmed cod escapes, it must learn to catch food itself, so it may take longer than usual before it has grown enough to become sexually mature.”

The researcher also takes a reservation when it comes to the egg collection itself: 

“This study was only conducted over a short period in March, while cod has a longer spawning cycle with a peak in spawning. The start of the spawning cycle can vary between different local populations, and this has not been mapped for cod in and around Voldsfjorden.”

The breeding that farmed cod has undergone also makes it more difficult for researchers to investigate the effects of such an escape. 

“The genetic selection that the farmed cod has undergone means that it is not known whether it will spawn at the same time as the local wild fish, or whether it spawns earlier or later.” says Terje van der Meeren.

Reference 

Kevin Glover, Maria Quintela Sanchez, Terje van der Meeren, Alejandro Mateos Rivera, Anne Grete Eide Sørvik and Elisabeth Stöger. Genetic identification of cod and cod eggs after an escape event in Voldsfjorden in 2022. Report from marine research 2025-24.

The image on the left shows an egg sample. The eggs are at different stages of development. To determine species, DNA must be used. The top image on the right shows the hoof used when taking egg samples. Photographer: Terje van der Meeren / Anders Jacobsen / Institute of Marine Research

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