For generations it was the silver darlings, cured in salt, cooked in oatmeal or soused in vinegar that were the west coast fishermen’s catch of the day.

While the herring graced the dinner tables, the huge – and fast – Atlantic bluefin tuna that gobbled them up at sea once made for fine big game hunt for deep sea anglers.

As herring numbers fell, so did the bluefin tuna. Once common, they had almost completely gone from Scottish waters by the 1990s.

Now, however, it seems the world’s most expensive and fastest fish have made a significant return, with growing numbers of sightings of bluefin tuna occurring along the west coast.

Rising numbers raises the possibility of a potential return to days when anglers were allowed to hunt and catch bluefin tuna in British waters.

The most recent was spotted in mesmerising drone film captured by the crew of Basking Shark Scotland, a tour boat searching for basking shark with television nature presenter, Steve Backshall, on board.

The vessel was in calm seas near Coll last week when the surface of the water was broken by the huge bluefin tuna. Backshall, presenter of BBC TV's Deadly 60, who had spent a week with the crew searching – without luck – for the huge basking sharks, tweeted his delight at the sighting to his 146,000 Twitter followers.

The spot followed the discovery of a dead Bluefin tuna measuring around 6ft on a Vattersay beach a fortnight ago.

However, they are not the only relatively recent sightings: in January, an 8ft long Atlantic bluefin tun weighing 30 stones was found dead on the beach at St Fergus near Peterhead. The fish, which if it had been the right quality of bluefin tuna, could have had a value of as much as £1.8 million, is thought to have perished in the low temperatures.

And in October last year, a bluefin tuna weighing an estimated 300kg - 47-stone – was caught in a fish farm off Great Bernera in Loch Roag, Lewis.

The huge fish, some 50 times larger than the salmon in the pens, was caught by farm workers and released back into the sea.

It’s thought it ripped through the pen’s netting as it chased mackerel at high speed.

Bluefin tuna, with their torpedo-shaped, streamlined bodies, are one of the largest and fastest fish on the planet. Known as the ‘Ferrari of the seas’, they are capable of travelling at almost 45 miles an hour.

While its flesh is highly prized in the world’s most luxurious sushi restaurants, the species is classified as “endangered” by the International Union for the Conservation of Nature.

At present, there is no quota for British vessels catching bluefin tuna, and any that are caught must be returned to the sea.

However last year Department for Environment, Food and Rural Affairs scientists suggested that by 2050 climate change will bring major changes in commercial species’ distributions in the North Sea.

It raised the prospect of Scotland’s warming seas attracting higher levels of bluefin tuna to replace species such as cod.

That has led to suggestions that 'big game' angling in British waters could return, with bluefin tuna at the top of the anglers' wish list.

Morven Summers of the Hebridean Whale & Dolphin Trust said: “While sightings of tuna are rare, they’re not unheard of; we occasionally receive reports of the fish through our recording app, Whale Track.

“We’ve also recorded a school of tuna during a monitoring expedition on board our research vessel back in 2019, and one also washed ashore dead on the southern coast of the Isle of Mull in 2011.

“In September 1989, a 400lbs tuna was caught off the Isle of Lewis.

“Historically, bluefin tuna did frequent our waters, with a commercial fishery running pre-wartime.”

She added: “It’s incredibly difficult to attribute cause and effect with marine wildlife – the complex marine environment makes it very challenging to determine the root of species increase/decrease, range expansion and so on.

“This is underpinned by the fact we still understand very little about the marine environment and the creatures that live there. “That is why it’s vitally important that we record the species we find in our waters, monitor over a long-time and build a better understanding of what’s going on.

“Our free and user-friendly app, Whale Track, is one way to help get involved with this citizen science undertaking.”

Bluefin tuna were once common around British waters, attracted by large shoals of herring. There numbers were so high, that ‘big game fishing’ became a fashionable pursuit, with 'The Tunny Club' attracting wealthy and famous to take to boats in search of the largest fish.

Some were extremely successful: the British rod and line record for a Bluefin tuna is 851lbs, caught in the North Sea in 1933 by a Mr Mitchell-Henry while fishing from a ship’s rowing boat, 50 miles offshore and alongside the herring fleet.

While currently UK vessels must not target bluefin tuna, a Marine Scotland license allows for a small number to be caught, tagged and realised as part of research and data collection.

Western Isles community company Harris Development Ltd has permission for three boats to take anglers out to catch the fish, with the information gathered potentially used to support the case for tuna fishing tourism in the area.

The Angling Trust and Bluefin Tuna UK has called for the UK Government to consider a “catch and release” system which would allow anglers to hunt the huge fish.

Bluefin tuna have also been increasingly seen in Sweden, Denmark, Norway and even Icelandic waters where tuna numbers collapsed in the 1960s.

Bluefin tuna is highly prized in Japan, where a single bluefin tuna recently sold for £2.5 million.

Quite unlike albacore – the fish which turns up as canned tuna – bluefin tuna has distinctive marbled flesh and a range of cuts which deliver different textures and flavours.

According to The Angling Trust: “There now exists a real opportunity to establish a world-class, sustainable, valuable live-release recreational fishery in our waters.

"In conjunction with a parallel scientific research program, this would not only contribute significantly to our knowledge of these tremendous fish but would bring substantial economic benefits to often hard-pressed coastal communities dependent upon tourism.”