There was barely a breath of wind to ripple the surface of the calm waters of Lerwick harbour – a peaceful precursor to the horrors that would soon unfold.

It was Monday, 16 July, 1832, and for the fishermen on the east side of Shetland, the idyllic summer scene – one of the most beautiful mornings of the summer so far – meant conditions were perfect for heading for the open sea, on the hunt for cod.

Salted cod, recalls Shetland-based writer John Goodlad in a new book which explores the massive impact the very humble dish of salted fish had on moulding everything from Shetland’s wealth to culture and society, was huge business.

Barely eaten by Scots today, dried, salted fish was once a staple part of the national diet and a massive export business – demand was at a peak from Spain and Portugal.

What the fishermen on Shetland’s east coast did not realise on that July day, however, was a heavy Atlantic swell had formed to the west – often an ominous sign of a severe storm on the way.

The crews would normally sail to the ‘haaf’ fishing grounds but with so little wind that day, they faced a gruelling 30-mile row in their sixerns, fragile open boats that trace their roots back to the classic Viking longship.

Once there, they found the sky in the northwest had turned dark. Before long, the calm had given way to a howling wind, violent hailstones and crashing waves.

The storm raged for five days, putting the entire fleet in jeopardy and picking off one sixern after the next.

“It was ultimately hopeless,” says Goodlad, a descendant of Shetland herring fishermen, former CEO of the Shetland Fishermen's Association and, latterly, a fish farmer.

“It seemed that the best a sixern crew could do was temporarily postpone drowning in exchange for a few more hours of utter terror. It was a brutal choice.”

The storm claimed 17 sixerns and 105 men. Those who made it back to land were so shattered they were unable to stand and had to be pulled from their boats by helpers.

Tammy Hughson, his sons Willie and Lawrie from the island of Whalsay were among those fortunate to be hauled on board a passing Dutch vessel, the Edwards. For them, recalls Goodlad in a book that follows the surprisingly fascinating story of how salt fish exports transformed life in Shetland, the journey was just beginning.

The storm was disastrous, leaving families without breadwinners and widows with bills from wealthy lairds for lost fishing lines that fishermen had bought on credit. At home with their seven children, Tammy’s fearful wife, Charlotte Kay, feared the worse. On board the Edwards, however, her husband was trying – and failing – to persuade his Philadelphia-bound saviours to switch course for Lerwick.

“By the time they had arrived in America, the Shetlanders had fully recovered and were anxious to get back home as soon as they could,” recalls John. “But that was not going to be easy; they had no money, and their only possessions were the clothes they were wearing.”

It would take months for father and sons to secure a passage across the Atlantic. They arrived first in Liverpool, made their way to Leith and, on Christmas morning, finally arrived in Shetland.

“Arriving safely in Lerwick harbour that morning, there was incredulity that this crew, thought lost in the July gale, had survived,” John adds.

The episode is just one of many personal stories that reflect the ups and downs of a fishing industry that put generations to sea to feed an insatiable appetite for a salty dish that few today have even tasted.

“People find it extraordinary today, but long before ‘just in time’ supply chains and frozen food, salt fish was common, a very good source of protein, and easy to salt and dry,” says John.

“And Shetland built a huge industry around it.”

Salt cod was in high demand from Portugal and Spain in the early 19th century, and Shetland’s fishermen supplied it in vast numbers for export.

On their doorstep, however, was another fish – herring – which Dutch vessels like the Edwards and fishermen in places like Wick, were already taking advantage of.

“Shetland had a huge cod fleet,” recalls John. “But within a matter of ten years it would all change when Shetlanders began to fish for herring.”

Demand from Spain and Portugal for salt cod dwindled as new markets for salt herring emerged in Russia, Poland and Germany.

From being a hub of cod fishing, Shetlanders embarked on a flurry of activity that would see the island become known as ‘the herring capital of Europe’.

“Shetland was one of the biggest cod fisheries in Scotland,” adds John. “Some years would see up to 12,000 tonnes of cod brought ashore and processed there – that’s about two or three times the total Scottish cod quota at the moment.

“Eventually fishermen realised there was more money to be made fishing for herring than cod. As soon as there is the chance to make more money, it takes off incredibly quickly.

“Within ten years, it’s all about herring.”

The switch transformed Shetlanders’ lives, he adds.

“Herring exploded onto the scene. The fisheries equivalent of the big bang, its economic and social consequences were profound.”

Drift nets made herring were easier to catch and money poured in giving fishermen, who until then had worked for lairds and often supplemented their income by smuggling brandy, the chance to own their own boats.

“From nothing to a fleet of more than 300 herring boats in less than ten years – it was as if the Californian gold rush had arrived in Shetland,” he adds.

“Herring came to dominate the Shetland economy in a way that no other industry had done before or has done since.”

At its peak, more than 2 million barrels of salted herring a year were being exported from Shetland – a third of the Scottish total. Alongside was a huge processing industry.

“The men were able to have their own boats and money was spread much more evenly throughout society,” adds John.

“For the first time women played a huge role, they were able to earn a living, and younger women travelled to ports where herring fishing took place.

“It was liberating - they worked hard, the pay could be poor but it brought huge social change for women.”

Eventually, however, demand fell, the herring fleets would dwindle in number, and the infrastructure that supported them on land virtually disappear.

Today there is little physical remains to show for Shetland’s herring boom other than the Swan, a classic Fifie, some 20 metres long, built in 1900 and restored in 1996 as a sail training vessel.

The book, he adds, aims to explore the history of the salt fishing industry in Shetland and the lives of the people in it – from those who faced the turbulent seas in search of their catch to artists, musicians, poets and writers inspired by it.

“Ordinary people did extraordinary things,” adds John. “Salt fish, boats and fishing would connect Shetland with the rest of Europe and become a crucial part of our society, culture, economy and cuisine.”

The Salt Road by John Goodlad is published by Birlinn