Jellyfish blamed for deaths of 200,000 Scottish salmon

String of Pearls species believed to have killed more than three million fish in Norwegian farms since winter of 2023

A jellyfish species has killed more than 200,000 salmon in Scotland in what is believed to be the single worst incident of it type, campaigners say.

The String of Pearls Jellyfish (Apolemia uvaria), also known as string jellyfish or barbed wire jellyfish, has struck two Scottish salmon farms, according to The Green Britain Foundation.

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It says the species has cause “havoc” for Norway's salmon industry - as jellyfish killed more than three million salmon in Norwegian farms in the winter of 2023.

Footage released by the foundation just two days before the jellyfish attack was officially detected shows tonnes of salmon of varying sizes being removed from the site.

The String of Pearls jellyfish has been blamed for the deaths of hundreds of thousands of salmonThe String of Pearls jellyfish has been blamed for the deaths of hundreds of thousands of salmon
The String of Pearls jellyfish has been blamed for the deaths of hundreds of thousands of salmon | Getty Images

The string jellyfish “unleash a devastating assault” on salmon, as their venomous tentacles inflicting excruciating burns on the fish's skin, eyes, and gills.

Trapped in densely packed pens, the salmon are unable to escape the relentless stings, leaving them with gaping wounds and immense stress.

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These injuries render the fish highly vulnerable to infection and disease, often resulting in a slow and agonising death if left untreated.

Animal experts describe the attack as "a true horror experience for animals with no means of escape."

It is believed to be the single worst incident involving these jellyfish on a farm in Scotland.

Dale Vince, founder of the Green Britain Foundation, sees this event as further evidence of the need for stricter oversight of the salmon farming industry.

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Campaigners say the incident highlights the urgent to phase out open-net farming.

The recent reports from Norway indicate the jellyfish threat to salmon farms is ongoing and potentially increasing.

In late October 2024, Norway's regulator, the Norwegian Food Safety Authority, warned salmon farmers to prepare for jellyfish attacks.

The authority advised farmers to put measures in place to deal with the impact of jellyfish on their fish stocks, as recent attacks by string jellyfish had killed a large number of salmon.

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The authority reported that jellyfish had been observed in numerous production areas, causing severe burns to the skin and gills of salmon, putting them at high risk for infection and disease.

A spokesperson for the owner of the one of the salmon farms involved acknowledged jellyfish blooms can affect salmon health in several different ways.

"To manage this emerging threat, intensive monitoring programmes are in place at Mowi's salmon farms across Scotland," said a spokesperson for Mowi Scotland.

"There are daily tracking efforts, which involve water sampling, species identification and counts, and temperature and oxygen monitoring at various depths.

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''We analyse trends daily to anticipate and mitigate conditions that might lead to harmful blooms."

A spokesperson for Salmon Scotland said: “Scotland’s salmon farmers have been upfront about the challenge of jellyfish and have invested hundreds of millions of pounds in a range of measures to protect their livestock from these naturally occurring organisms.

“In 2024 Scotland’s salmon farmers recorded the best survival rates for four years, showing that the environmental challenges that affected salmon production in 2022 and 2023 are thankfully behind us.”

A Scottish Government spokesperson said the health of farmed fish was a priority: "While we do not have comprehensive information regarding which species of jellyfish are present on fish farms in every case of reported mortality, the salmon farming sector is focused on better understanding the impact of jellyfish as a cause of mortality.”

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