This was the scene after tens of thousands of fish were washed up on a four-mile stretch of the Manx coastline.
But pollution has been ruled out as a cause.
Cyclist Dave Rielly said he got a bit of a shock on Saturday morning when he came across the dead fish on the beach for four miles heading north from Dog Mills as they had not been there the previous evening.
He immediately contacted the Department of Environment, Food and Agriculture, saying: ‘I was worried – I thought it might be something to do with poisoning.’
DEFA director of fisheries Karen McHarg attended the scene on Saturday.
She said: ‘It appears that a large shoal of juvenile herring has been driven onto the beach by a shoal of feeding mackerel.
‘The dead fish in the forefront of your picture is a mackerel. Bass do the same thing with herring sprats.
‘This does happen occasionally at this time of year and has been reported in other places around the island in previous years e.g. Peel.’
She said it was ‘a completely natural phenomenon’ and is in fact a good sign of flourishing stocks of herring.