Scientists have noticed an unnerving phenomenon in fish in Florida.
Scuba diver Gregg Furstenwerth had been out at night in November 2023 and noticed something unsettling in the water off the Florida Keys.
What he saw was a pinfish swimming through a seagrass meadow, but the distressed fish was swimming round in upside-down circles.
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A curious Furstenwerth recorded the incident on his underwater camera.
Sadly it was not the last he would hear of it as he heard of several other similar incidents.
The incidents were focussed in a 35-mile stretch of water in the lower Keys, with one case also in the upper Keys.
Cut to March 2024, and scientists and locals working together have found some 44 species affected by the strange phenomenon.
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It's still not clear exactly what is causing the strange behaviour in fish.
Marine scientist Alison Robertson said: “Everybody wants to know what it is right now.
She added: "We're going to do everything we possibly can to work together to try and identify that so we can come up with solutions.
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"It is very strange to see such a prolonged event affecting so many different species.”
Watching the fish in such distress has also had an impact on Furstenwerth.
He said: "It's hard to process. I must keep doing this though. It's not in my nature to quit."
While it's not clear what is causing the problem at present, scientists are trying to rule out possible causes.
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One possibility is that it's an algal bloom of some kind.
Marine ecologist Michael Parsons specialises in algal blooms at Florida Gulf Coast University.
He said: “When you have distressed fish or a fish kill in Florida, the first thing people will think about… is a red tide."
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A 'red tide' is when algae bloom in huge numbers, releasing toxins into the water that can be harmful to marine wildlife and to people.
But in this case the indicators which would suggest a red tide were not there.
There also weren't any abnormally high temperatures, low oxygen levels, or parasites in the afflicted fish.
Parsons said: “Fish kills happen, unfortunately, all over the place.
“But in this case, we can't explain it by the usual causes. That's the strangeness of this event.”
Nonetheless, scientists are still working to try and figure out exactly what could have caused the fish to start dying off in such a strange way.
Topics: News, US News, Animals, Science