In 1868, Parliament lifted all restrictions on sea-fishing, as to method and quantity of catch.

Within a generation, the trawl-net had joined a list of technological and social innovations – field enclosures, the spinning jenny, the power loom, later the motor car, television and computer – that seemed to divide a paradisal past from a depleted present. Published in 1914, John MacDougall Hay's Gillespie makes trawling not only the agency of the lead character's greed, but also of a small West Coast town's moral downfall. A generation further on, and at the bleak height of another European war that turned the North Sea into a battlefront, Neil Gunn's The Silver Darlings looked back to a time when the seas round Britain seemed an inexhaustible source of food. Hay was untypically prompt in doubt and dissent. No less a figure than Sir Alister Hardybegins the second volume of his New Naturalist study of The Open Sea with an idealised version of the trawl net as a vast test-tube of marine research. Even in 1959, Hardy seems sanguine about a future for British fishing, as the summer herring catch, a key element of North European trade and a staple of food for the poor, had collapsed by the end of the Second World War.

It is tempting to believe that what Smout and Stewart call in an early chapter "the Firth of plenty" was always teeming. To listen to old men in Port Seton or the East Neuk of Fife, it was once possible to walk dryshod from Dunbar to Kingsbarns on the backs of herring. It was never so. Fishing is testy and dangerous work and its returns dangerously unpredictable. There were deep and long slumps, scientifically unexplained but possibly geological, in the shoals that fed and capitalised the Forth estuary and its surrounding settlements.

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However, even if other environmental factors contributed to the decline and then virtual disappearance of the great oyster scalps that used to be mentally pegged out on the shores and waters north of Edinburgh (imagine drawing lines in the sea and squabbling over them!) the radix malorum is always human greed. Hay's Gillespie Strang, the "souple" capitalist of "Brieston" (the book is still banned in Tarbert, when town elders recognised a Caliban image in the looking glass), is a familiar figure.

Less so is the real-life personage of William Carmichael M'Intosh, professor of natural history at the University of St Andrews and the first full-time fisheries scientist in a British university. Undergraduates once fought pitched battles with local fishermen in defence of M'Intosh's reputation. A protégé of Thomas Huxley, who with Lyon Playfair had deemed the seas too rich in resource to be degraded by merely human activity, M'Intosh deserves to be as well remembered as D'Arcy Thompson, another weel-kent St Andrews figure.

Christopher Smout is their worthy successor, on the historical side. With his collaborator Mairi Stewart, an expert in the Scottish woodlands and the social history of Scottish forestry, he has created a richly detailed history of a key locus in our national evolution. The Firth of Forth is less than 300 pages, but it shoals with detail and rich illustration, from classic Hill and Adamson portraits of fisher folk (which look like production photos from Peter Grimes or maybe Albert Herring) to diagrams of drift and purse nets, and maps of the towns and villages that a king once likened to rich beads on the fringe of a beggar's gown.

We have, thanks to activism, crisis-science and the work of historians such as Smout and Stewart, begun to rediscover the sea. The motor car and the aeroplane diminished its importance. Greed and uncontrolled pollution degraded its plenty, in ways that suggested a later, more pessimistic Huxley. Faced with the equivalent of one of those psychological experiments where one can see only two profiles or an hour-glass but never both at once, we came to assume that the land was important and the sea an absence. Reverse the perception and the history of Scotland, from Columba to the asset-stripping of both Forth and Clyde, was dominated by water. The old cartographers produced an image of Scotland as two semi-islands, narrowly joined by the choke-point of Stirling Bridge. As Smout and Stewart remind us, there was a time, in geological history, with Loch Lomond flooded by the sea, when it was possible to walk across Scotland in a matter of hours rather than days. Even now, the tidal influence reaches very far inland. The two great "firths" are shaping forces.

For a lay reader, or one with a spotty and inconsistent understanding of environmental science, several key perceptions arise out of the Firth of Forth. There is a certain consensus of gloom and decline. We think in terms of a movement towards extinction, but Smout and Stewart make clear that the process is more staccato and subject to dramatic reversals. The Bass Rock was not always white with gannets (one of the great sights of natural history, anywhere). It was once dark and only spotted with solens. Similarly, the eiders which humph and flute in dinner-jacketed gentleman's clubs round every estuary harbour and bay were once relatively uncommon. The only people who hate them – and this is a clue – are the mussel-farmers. Similarly with goldeneye, one of our most delightful birds.

Another key impression that surfaces in Smout's and Stewart's pacy account, almost unnoticed, is that a certain familiar contrast between Forth and Clyde simply doesn't stand up. In one of the loveliest passages in Alister Hardy's The Open Sea II: Fish And Fisheries, he says: "I know of no sight in all industry to equal that of the hauling of the herring nets unless it be the running molten metal in the foundry." Hardy was in no doubt that fishing was an industry and as dynamic as metallurgy. We tend to think of the Clyde as being industrialised and the Forth littoral as somehow ... bucolic? douce? relatively undeveloped? The reality is dramatically different, a perception brought home most sharply by a 1909 photograph of the bay at Rosyth, looking peaceful and untouched. When Glasgow was still a village, Edinburgh was a city to rival Norwich and Bristol for population, trade and industry.

There is far too much in The Firth Of Forth to summarise. Chapters on pollution, the Bass, the Isle of May and seals (almost as unpopular as eiders in some quarters, but another species once as rare as mermaids) are brilliant free-standing essays, but the book as a whole has a consistent narrative drive that brings a sense of context, historical mediation and regional pride, detectable even by a West Coaster. And at £14.99, it's almost as cheap as herring once was.

The Firth Of Forth: An Environmental History

TC Smout and Mairi Stewart

Birlinn, £14.99