Barbed-wire jellyfish (Apolemia uvaria) have invaded two Scottish fish farms, killing nearly 200,000 salmon.
The jellyfish, sometimes called String of Pearls Jellies or string jellyfish, struck the two farms in Invertote and Muck between late October and early November 2024. According to the Socttish Fish Health Inspectorate, the Muck site lost 163,232 fish, while the Invertote site lost 32,000. To stem losses, workers harvested surviving fish at both sites.
The barbed-wire jellyfish live in colonies that can reach 9 feet in length, attacking prey in the manner of a net. Their stings are painful and, in farmed salmon, often induce contagious disease.
The increasing frequency of jellyfish attacks has bedeviled the salmon farming industry, prompting the development of innovative technological responses like the jellyfish-stunning fences that are currently being tested. In Norway alone, millions of farmed salmon have died as a result of injury or illness caused by jellyfish attacks.
In late 2024 the Norwegian government warned the nation’s aquaculture sector to be prepared for barbed-wire jellyfish attacks after getting reports of the animals in coastal waters. The country’s Food Safety Authority then urged farmers to take proactive steps, including euthanization, to avoid attacks.
In Scotland, where El Niño has warmed waters, 1 million salmon died at two adjacent Mowi farms after micro-jellyfish attacks in October 2024.
In response to a request for comment about the matter from SeafoodSource, a Scottish Government Spokesperson said, "our vision for sustainable aquacutlure reflects farms fish health as a priority. Micro jellyfish in general can cause damage to the gills of the fish, which has direct implication for fish health and which also increase susceptibility to wide health issues and mortality. 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."
