A TUNA fish weighing 180kg – more than 28 stone – washed up near a sailing club.

Experts do not know how the two-metre-long fish ended up on the Sussex shore but said it was positive news for the threatened species.

The Atlantic bluefin tuna was already dead when it stranded near the Thorney Island Sailing Club in Chichester Harbour on Wednesday.

The fisheries patrol boat Watchful hauled the colossal fish on to its deck with a winch before transporting it to Shoreham Port.

Sussex chief fisheries officer Tim Dapling said the find was “unusual and positive”.

Atlantic bluefin numbers have drastically declined over the past century due to overfishing.

They were classified as endangered until 2015, when they were upgraded to “near-threatened”.

Mr Dapling said the sighting could indicate an improving ecosystem in the Channel.

The Argus: The colossal tuna was found in Chichester Harbour. Photo: Sussex IFCAThe colossal tuna was found in Chichester Harbour. Photo: Sussex IFCA

“Although it is a pity the fish was not alive, it is first time we have encountered at close quarters a bluefin tuna specimen in Sussex coastal waters,” said the officer, of the Sussex Inshore Fisheries Conservation Authority.

“The adult bluefin tuna are at the top of the marine food chain and the increasing presence of top predators typically indicates the improving health of ecosystems.

“Of course this was just one fish, however I’d be surprised if it was the only one in Sussex waters.”

Mr Dapling said it is not known how the large tuna died or how it ended up in the shallow waters of Chichester Harbour.

But he suspected the fish became disorientated after entering the harbour to feed on mackerel and bass.

“Presently we have spring tides and at low water the channels of the harbour can be relatively shallow and narrow,” Mr Dapling said.

“A fish of this size and species is used to open sea areas where it can swim unconstrained to hunt prey.”

Fishing Atlantic bluefin tuna is illegal in the UK. Any tuna caught by vessels or anglers must be returned to the sea alive and unharmed.

The fish found in Chichester showed no signs of damage caused by fishing gear.

Officers took samples and measurements before disposing of the carcass.