The South African government has identified the creature as the lethal evileye pufferfish and has warned locals to stay away.
Gridley, a scientist who moved to Africa in 2009, estimated that hundreds of the deadly fish were washed up on the shore.
“The beach is 200 meters from our house and we were on a family walk,” she said. “I can’t say how many were there as I only looked in a small area – I was with my kids and dog, and prepping for fieldwork so it was a short visit. But if you did count it would have exceeded hundreds.”
South Africa’s Department of Environment, Forestry and Fisheries said in a statement that the species carried a killer neurotoxin called tetrodotoxin.
Tetrodotoxin is a poison that is more lethal than cyanide. It causes death by respiratory failure after paralyzing the diaphragm.
“The fish mortalities in False Bay are exclusively of the evil-eye pufferfish with counts of 300 to 400 dead fish per km of shore. These dead fish all carry the deadly neurotoxin tetrodotoxin and should not be eaten; death comes usually by cardiac arrest. Beach dog walkers are strongly advised to keep their pets away from them. If one’s dog does eat whole or part of a pufferfish, immediately induce vomiting and rush your pet to the vet,” the statement read.
One dog has already been killed as a result of the mass stranding.
The cause of mass stranding remains a mystery.
Previous mass strandings have been caused by red tides – an algal bloom that changes the water’s color and produces natural toxins.
But the ministry statement said that “there are no reports of any adverse water conditions or red-tide toxins that may have caused this.”
“There is now an important role for citizen scientists in reporting these events through social media. We are learning a lot more about the marine environment these days from such reports. If possible, collect photos and videos which can then help to identify species, and offer interesting insights into what’s living in our oceans,” Gridley said.