Invertebrate fisheries are easy to manage and initially there's a good return. But the habitat becomes less stable, too, more vulnerable to disease, parasites, climate change.
Schools are breaking up, the gulls are circling watchfully and the deep fryers are ready in all ten of West Bay's fish and chip outlets.
In good weather, the kiosks around this small West Country harbour will serve over four thousand cod meals in a week.
The most English of dishes may have been introduced by Sephardic Jewish immigrants, but the fish itself, at least, has traditionally come from what the English sit and look at while they munch: namely their own coastal waters.
The relationship between those fishing grounds and the cod we continue to eat has never been more precarious. A new report from the University of Plymouth has shown a dramatic shift in the Channel's ecological state over the last 90 years.
The Channel's fish stocks are dangerously low
In southern English and northern French ports, 48% of landings in 1920 were of cod, haddock and hake. The figure in 2010 stood at 14%. The UK now has to import over 100,000 tonnes of cod a year.
Just a quarter of what we eat comes from British waters, and those are from dangerously low stocks. Specimens over ten years old are almost never caught here - the fish can live up to twenty years.
The UK's fishing industry has reacted to such news as it invariably does, with scepticism. In Iceland, where they listen to their biologists, the result is what this year's crowds in West Bay will find inside all that batter.
The essentials of the science are not complicated for anyone who wants to understand. 'Mean Trophic Level' is the position of any given organism in its food chain.
Cod is a high Trophic Level species, a top predator: its rich diet accounts for the firm meat for which it is prized. As fishing fleets industrialised in the early 20th century, they were able to exploit cod at greater distance from home ports and at greater depth.
Problem? What problem?
But increased landings masked the decline in stocks overall. More distant stocks also eventually began to decline and 'fishing down the web' commenced. Shell fish and invertebrates, which made up 3% of landings in the Channel in 1920, now make up 47%.
Those figures aren't all about what's in the sea. Market mechanisms create 'perverse incentives' which reinforce the shift to reduced biodiversity. By raising the value of species like scallops or crab it becomes profitable to keep degraded marine habitats as they are.
The mean Trophic Level of fish caught in the Channel has dropped faster over the last 90 years than anywhere else in Europe.
Carlotta Molfese, the report's lead author, explains: "As with monocultures on land - these invertebrate fisheries are easy to manage and initially there's a good return. But the habitat becomes less stable, too, more vulnerable to disease, parasites, climate change."
The trouble with simplifying the sea
The lobster ranches on the North East coast of the United States, the snow crab, scallop and prawn fishery which replaced cod off Nova Scotia, the nephrops prawn fishery in the Clyde - all of these have proved both highly profitable - and highly vulnerable to disease.
The new report shows that landings of sharks, rays and chimeras in the Channel have gone from 34% of the catch in 1926 to 6% in 2010. The collapse in biodiversity is the larger context in which these figures should be understood.
The findings were simultaneously played at full volume by the press - "Fishermen Scraping the Barrel" in the Telegraph - and condemned as poor science by Seafish (stated aim: "refute ... any negative messages about the UK seafood industry"). Some scientists have also expressed reservations about the data, especially as 'maxxed up' by the media.
'Poor science' is science the industry would rather ignore
Most forthright in their denunciations have been the very industry spokespeople who have argued that dredging should resume in Lyme Bay's protected area. Even after science put the speed of recovery there beyond doubt.
In a letter which the Western Morning News declined to publish, Malcolm Gilbert, a Cornish fisherman with sixty years' experience, wrote: "I believe one of the core failures of EU fisheries management is that the entire process is far too industry-captured."
He has watched the abundance and age structure of fish populations altering and drawn his own conclusions.
The industry itself, it should be said, routinely bases its own stock assessments on catch data. The uncertainties inherent in such data are not disputed by the researchers of this paper or anyone else.
But the industry's real objection here is that the general trend which has been identified - namely, the undoubted decline of high Trophic Level fish in the Channel - is one it would rather not hear about. So suddenly catch data are not problematic but worthless.
A greater role for the smaller boats and the natural conservationists who operate them can only be achieved through setting clear boundaries to what 'the industry' (and its spokespersons) can legally get away with.
The Marine Protected Area and Blue Marine initiative in Lyme Bay add up to an excellent example, so far the only one, of how well this can work in practice.
The government's 'vision'
The government is currently consulting on the south coast Marine Plan, which will determine policy until 2036. I would recommend the current 'draft vision' if only for what it tells us about the government's current thinking on this.
The "overall aim" of its "High Level Marine Objectives", for example, is "delivering sustainable development". In planning documents "sustainable" is now officialese for "profitable". This University of Plymouth report is a timely and welcome reminder that profitable may mean anything but sustainable.
The government's 'vision' is of a situation in 2036 where "the protection of natural habitat has been maintained and, for those areas that are not currently afforded protection, enhanced."
This sounds promising - but in fact, it's the reverse. It promises no more effective form of protection than is afforded by 'Marine Conservation Zones' - which have, for the most part, yet to deliver any protection at all.
A parliamentary committee recently concluded that the present legislation is woefully ineffectual.
The suggestion that "responsible use of sound science" might also serve as a High Level Marine Objective has, significantly, been dropped from the present draft. If you don't like the sound of that, well, the consultation closes on July 31st.
Environmental laws that actually work
But you might want also to consider the work of Polly Higgins in this context. The TED lecture she recently gave in Exeter is a good introduction. A professional barrister, she argues that the wilful destruction of natural habitat, of the kind advocated by our industry spokespersons, will only stop when it comes to be viewed as the criminal activity which we all know it to be.
She has suggested the term 'ecocide' to describe such activities and suggests that an international law should override the 'right' of any company, however huge, to enrich itself irresponsibly at the environment's expense.
The state, she argues, should have a legally binding duty of care towards the natural environment, just as it has towards its human population. She has taken it to the UN and to national governments.
Whether our own government means anything at all with its latest 'consultation' remains to be seen. If you too are doubtful then get in touch with them, if only to tell them all about ecocide.
Perhaps such talk suggests a world of legal abstractions where you don't feel at home quite. Let me end, then, with an immemorial West Country story to remind ourselves of what ecocide has already done in the Channel.
About a thousand years ago an Anglo-Saxon monk at Cerne Abbey, in Dorset, struck upon an idea as to how he might interest novices in learning Latin. He had been sent to Cerne to raise educational standards and one of his ideas was a very ingenious one. He interviewed a fisherman, somewhere not too far from Wareham, and then used the text as a translation exercise.
'Aelfric's Colloquy' has survived and it offers an intriguing picture of how the West Country's aquatic environment looked long before 'the industry' was ever thought of. Here is some of it in modern English:
"What sort of fish do you catch?"
"Eels and pike, minnows and mullet, trout and lamprey. Tench. And whatever lives in the river."
"Why not fish in the sea?"
"Sometimes I do, but not often, because it is a long trip for me to the sea."
"What do you catch in the sea?"
"Herrings and salmon, dolphins and sturgeon, oysters and crabs, cockles, plaice and flounders, lobsters and many others ... "
The fisherman goes on to explain why he doesn't hunt the whales which at that time abounded in the Channel.
Aelfric's colloquy offers a tantalising glimpse of an abundance and a biodiversity which has, even now, not vanished entirely. And the amazing speed of recovery in Lyme Bay gives some idea of just how quickly we might get some of it back.
Dredges of the mind
But it surely also points beyond, to something even richer, even stranger. The degradation isn't only 'environmental'. Attention to and concern for our surroundings are above all habits of mind. They too can easily be lost. Science as an honourable, independent pursuit, historical imagination, political courage - these also are habits of mind that we have to constantly relearn.
It was our own degraded sensibilities which allowed the dredgers, and the governments which deferred to them, to get away with it for as long as they did. There are dredges of the mind we need to exclude, too.
And then, who knows? As scientists and fishermen alike have been in Lyme Bay, we might be astonished by how quickly the recovery begins.
Also by Horatio Morpurgo: Taking the 'conservation' out of Marine Conservation Zones.
Horatio Morpurgo is a journalist and campaigner. He lives about a mile away from Lyme Bay and was involved in the successful local campaign to exclude the scallop dredgers from Lyme Bay and establish a Marine Protected Area.
Horatio's book Drake's Graffiti (Erewhon, 2010) situates Marine Protected Areas in the longer story of the West Country's relationship with the sea.