Huge numbers of the small silvery fish began coming ashore at bays including Archirondel and Anne Port at the end of last week. There have also been reports of dead sand eels at the Ecréhous reef.
In a Facebook post over the weekend, the marine biology section of the Société Jersiaise said members had taken samples of the fish, which seemed to have been in good health when they suddenly died.
The specimens they sampled were all juveniles of the common local species, Raitt’s sand eel.
They were each between 4 cm and 9 cm long and ‘seemed to be healthy with food in the guts, and gills in good condition’, they said.
All the fish were decomposing when examined on Friday, indicating they had been dead for at least a couple of days.
Although it is not known what caused the deaths, pollution or a large algae bloom is considered unlikely.
In the post, the Société said: ‘What can have caused this? This is a difficult one to answer. The die-off seems to be a species-specific (and only juveniles) single event.
‘The fish seem healthy, with no obvious sign of disease or starvation. This suggests it is not a pollution event or due to illness. Toxicity from “red tides” [algae blooms] has been a cause of mass sand eel mortality in the UK but this is unlikely here as there is no sign of red-tide algae concerned and it is also generally a phenomenon of estuaries.’
They added: ‘Several people have mentioned lightning strikes as a possibility and, at present, this would be our best guess.
‘There have been several hundred lightning strikes recorded around Jersey in recent days (mostly 26/27 May but also 28 May). A strike directly onto a shoal of sand eels (or onto the sandbank in which they were sheltering at low water) could possibly cause this.
‘A similar mass die-off in Jersey many years ago also occurred following thundery weather. However, other causes should not be ruled out.’
Anyone who has seen other large numbers of dead sand eels from other locations or from before last Friday is being urged to contact the Société so they can narrow down where and when the deaths occurred. The group is also asking anyone with ‘thoughts or observations’ on the deaths to get in touch via their website, societe-jersiaise.org/sections/marine-
biology.
