The Tragedy of the Fish, The Politiken, July 2023
Poul Holm is a historian and one of the world's pioneers in the field of marine environmental history
When Poul Holm was hired as a curator at the Fisheries & Maritime Museum as a young man, he started going through the museum's collection to get an overview of what he actually had at his disposal. "And then I came across this net for catching sturgeon, and I thought 'what'?", he says. We Danes know sturgeon best as the source of caviar. They are huge, exotic, bottom-dwelling fish measuring many meters and hundreds of kilos that we associate with Russian rivers and lakes. The yarn turned out to come from a farmer on Mandø from around the 1920s who had used it to catch sturgeon in the Wadden Sea. "I've since found out that the fish auction in Hamburg received huge catches of sturgeon right up until the First World War. But right around that time it completely collapsed and now there are no sturgeon in the Wadden Sea or the North Sea anymore," says Holm, who is now a professor at Trinity College Dublin and one of the world's key researchers in the field of marine environmental history. In fact, sturgeon fishing was so promising that in the late 1800s, fishermen in Esbjerg were granted a sturgeon net for DKK 199.05 via the Danish Finance Act in an attempt to start a commercial fishery. But the fishermen were actually more interested in fishing for the huge stocks of haddock in the area. Later, the haddock collapsed and has never returned to the area.
The sturgeon and its disappearance is a small example of the enormous changes that the oceans have undergone over the last several hundred years, which scientists are only now beginning to fully understand: the ocean we have today is a shadow of the wealth that once was. A consensus is now emerging that the major commercial fish species have declined by 85-95% globally, and other species are probably in the same position, if not worse. "As a rule of thumb, you could say that we have lost nine out of ten fish," says Poul Holm.
This is also true in Denmark, where a major cultural fish like the cod hovers on the brink of collapse, and large parts of the seabed are described by experts as "a desert" or "a graveyard", but in earlier times were so rich in fish that it sounds like lies.
Historians and writers of the past have described how Øresund, the strait between Denmark and Sweden, was so full of herring in season that in some places - Skanør in Sweden and perhaps near Dragør - they could be scooped in baskets from the shore or taken with bare hands. A French knight passing through wrote with amazement that you could stand and "cut them up" with your sword.
That sounds like a gross exaggeration. But the huge shoals of herring both here and elsewhere in Northern Europe are so well attested in historical sources and through genetic studies that the stories can be reasonably true.
"Historians have laughed at this and said that it's all lies and Latin and 'oh, how they exaggerate'. But studies show that there was actually a collapse from a very high population around the 1500s. So it's actually quite correct that Øresund was full of herring," says Poul Holm, who, based on tax information from the period, has calculated that catches were 50,000 tons of herring annually - equivalent to several hundred million herring. We can't say what caused them to disappear. It could be climate change, it could be currents, it could be overfishing. But what we see again and again when we look at these historical stories is that they are not exaggerated. It has happened," says the professor.
The shifting baseline syndrome
It's not just fun trivia to bore someone with during a dinner party. It's information that is now starting to be used to create a proper baseline for the management of the fish we have left. Marine biologists and authorities have typically started from and researched what had good, solid data and catch statistics. This has limited their view of the past to the last 70 years. The unfortunate side effect is that it has given marine scientists a distorted view of what is the correct natural baseline - nature's untouched, virgin starting point.
This is known as shifting baseline syndrome, where we - scientists, fishermen and ordinary citizens - confuse our own past experiences of the state of nature with an 'untouched state of nature' and dismiss the experiences of previous generations as 'tall tales'. In recent years, there has been a growing realization that we need to look further back in history, and marine biologists are now starting to work with historians and archaeologists to get a more accurate picture of what was. For example, DTU Aqua in Denmark has started digging dusty, yellowed reports out of the archives to get an insight into what was caught near the coast in our fjords, for example, something that modern data is completely silent on.
A sea full of rays and sharks
Today, many Danes probably have an idea that the sea around Denmark is all cod, flounder and sandy bottoms, while exotic sea creatures belong in Thailand's diving destinations or on whale watching safaris on the American West Coast.
But in environmental professor Callum Roberts' book 'Unnatural History of the Sea', the ocean off the coast of Europe a few centuries ago is described as teeming with exotic wildlife that a modern fisherman wouldn't recognize. Fishermen in the 1700s scouted in the spring for the large plankton-eating sharks, the basking sharks, which arrived in their thousands, signaling that the shoals of herring, sprat and sardines were in the water in search of plankton.
Historians of the time described the herring shoals as columns 8 kilometers long and 5 kilometers wide that looked as if the sea itself was rising up in a silvery glow.
And with the schools came the predators: mackerel, cod and bluefin tuna, but also dogfish, herring sharks, thresher sharks, mako sharks, blue sharks and even eight to nine meter long 'Jaws'-sized great white sharks. Thousands of pods of porpoises and dolphins, groups of enormous fin whales, minke whales and even blue whales arrived, looking to supplement their krill diet with small fish.
The North Sea floor from the English Channel all the way into the Kattegat was covered almost everywhere with mussels and oysters, reefs of rock and coral and meadows of sea plants. But with the arrival of trawling gear, the bottom was turned over so frequently and several times a year that today the North Sea has turned into sand, gravel and mud.
In the Wadden Sea, the shallow sea from the Netherlands to Esbjerg, a special type of polychaete worm, Sabellaria spinulosa, had built huge coral-like limestone reefs over thousands of years, and until 100 years ago the waters were filled with unique life from the thousands of species that lived in the reefs to large animals like dolphins, right whales, sturgeon, haddock and species of ray several meters long - "as big as front doors", writes Callum Roberts.
Now, most of the Wadden Sea's biotopes have been leveled by seven decades of shrimp trawling and mussel scraping. The bottom is sand and mud, and flatfish dominate. But you can still see pieces of coral reef washing ashore.
The tragedy of the trawl
"Danish waters are a desert compared to what we've had. We've been losing biodiversity at a rapid pace, and just in the last 100 years, the situation has completely changed. If you look at catch statistics, we can see that a large number of fish were caught that we no longer have as commercial species at all. Also, the seabed has completely changed. In the Kattegat, we have documented that there were reefs and oyster beds everywhere, but now they are gone," says Poul Holm, Professor of Marine Environmental History.
The dramatic impact of humans on the sea is not only new: the professor's research has helped to show that fishing pressure in Europe in the Middle Ages and North America in the 18th century, for example, was much greater than previously thought. This has helped to change the idea of what an unaffected, virgin fish stock must have looked like. But it was trawling with motorized cutters from the late 1800s that really changed the 'balance of power' between man and the sea. Before then, fishing was always limited by wind and current, and there were practical limits to how far away from your home port you could fish. At the same time, fishermen couldn't easily transport fresh fish to other cities.Technology changed everything: With a motorized trawler, a fisherman could fish an empty area of ocean and then simply move his fishery further out to sea to new, virgin stocks. And once the trawler came ashore, the fish could be transported to big cities by rail, initially alive in water-filled tanks and later cooled by ice imported from Norway. Suddenly, any number of fish could be sold. Fishing exploded. In Denmark, the development was different at first. We specialized in fishing from our small blue cutters with gentle fishing methods for the flatfish that the other big fishing nations were not interested in. We "made a lot of money", says Holm, by selling high-quality sole, turbot and other good flatfish to the affluent markets in Northern Europe. It wasn't until the 1950s that large-scale industrial fishing for 'dirty fish' such as herring, sprat and sand eel made its breakthrough - the giant trawlers and floating fish factories that are at the heart of Danish fishing today.
Overall, this meant that globally we went from pulling 20 million tons of fish out of the sea in 1950 to around 120 million tons in 1995, says Holm. What's worse, about half of the biomass over the last hundred years has not been used for human consumption at all. It has been used as fertilizer for agricultural fields and later as feed for pigs, chickens and hens. "It has actually left as big a footprint throughout the 20th century as what we eat. It's a catastrophic exploitation of the ocean's resources," says Holm.
The potential for recovery
The decline in fish stocks is not just about there being fewer of each species, but that species composition is also changing significantly. Slow-growing large animals are being replaced by small, fast-growing animals that can reproduce before they are caught. Benthic life is changing from animals like Sabellaria spinulosa, which patiently build up the seabed in three dimensions over decades, to those that hide in muddy bottoms and can build up their populations quickly between annual scrapes from the bottom trawl. It's as if marine life is also afflicted with ADHD. But there is a positive side to scientists better understanding the magnitude of the ocean's decline: Now those making decisions about ocean management can quantify what the ocean can do when things are going well.
"I think the perspective of my research is that we can see what we have lost, but also what we can gain. What the potential is. And that's the other side of the shifting baseline syndrome," says Holm. If we know that the large fish stocks have the potential to grow ten times larger, then there is a much greater economic incentive to do ambitious management instead of pushing the stocks to their limits, as has been practiced in the 20th century. The math is simple: There is much more money in annually fishing 15% of the ten times larger haddock, herring and cod stocks of the past than 50% of today's small remaining stocks. But according to Poul Holm, it is an illusion to believe that we can get our original stocks and habitats back. "No, no, we have destroyed too much. And I don't think we have the political patience for it. We would have to withdraw completely from fishing for a period of time, and I don't think that's possible."
Still, there is hope, he says: For one thing, there are now so many examples of fisheries regulations working that the criticism is fading. And last December, the countries of the world adopted a major new UN treaty to protect 30 percent of the world's land, coastal and wetlands. "It's fantastic news that for the first time globally we have reached this agreement. The effect of freeing part of the ocean from fishing will be huge, because it creates huge areas where life can flourish," he says. "The ocean is resilient, more so than the land. On land, we can shoot all the animals we can see. Out in the oceans, fish can actually hide. So they're waiting for the opportunity to get going again and build up their population. That's the hope here. But of course, we have to give them time and chance, and we have to stop destroying their seabed," says Poul Holm.
Poul Holm
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