A man holding a big Atlantic sturgeon

Where are the big fish?

European waters were once brimming with big fish. Huge changes have taken place, and today’s fish are much smaller than only two or three generations ago.

The problem with understanding changes of life in the ocean is that we don’t see what’s beneath the surface. On the land we can see environmental change with our own eyes. That is why fishermen’s own records deserve attention.

The epic struggle of man versus fish: Hemingway’s The old Man and the Sea (movie cover by Warner Bros.)

Historical studies of several hundred years of fishermen’s logs, business records, monastic archives and other evidence of the industry itself reveal the scale of change in what we have extracted from the ocean. The story boils down to one rule of thumb: we have reduced total abundance of large fish – not just sharks but cod, tuna and all other major commercial species – by 90 per cent in the last 100 years. And the big fish are much smaller today than they used to be.

Skippers’ logbooks are a clear indication of the scale of change. In 1874 the British fisheries observer Edmund Holdsworth noted the first indication of change: ‘It has been observed that when any newly-discovered cod-bank is first worked some fish of remarkable size are pretty sure to be caught. … But monster-cod five or six feet in length [152-183 cm], as were at first frequently reported, are now very seldom met with.’

There is a strong correlation between length and weight of fish. A ‘monster-cod’ of five- feet would have weighed 37 kg and cod of six feet would have the astonishing weight of 64 kg. Such cod sizes are enormous in comparison to the cod caught in the North Sea today. The average for North Sea cod catches in the last fifty years was between 1.1 and 2.5 kg. The average North Sea cod is caught at the age of 2.8 years – it will only spawn at the age of three years – and is about 50cm long.

Similar declines are known for the ling – previously a popular fish for general consumption but now caught so rarely that is considered commercially extinct. The normal length for ling today is an average of 80 cm, down from a normal distribution in catches recorded in 1843-45 between 90 and 125 cm. That is a 30% reduction in length, which converts to much more in kg: a 94 cm ling weighs 6.1 kg while a 125 cm ling weighs 16.3 kg.

The History of Marine Animal Populations is a global project to establish historical baselines to understand how much ocean life has changed. We have documented fisheries in places such as Northern Russia, the Baltic, the Mediterranean, the North Sea, South Africa, New Zealand, the Caribbean and many other places. Everywhere the picture is the same. The effects of early industrial fisheries were more profound than we thought. Fishermen first took out the large animals and they are much reduced today ( The Big Fish are Gone, pdf, 3.6 MB). The impacts on big fish often happened a hundred years or more ago – long before modern scientific stock assessments came into practice. Haddock used to be abundant in the southern North Sea.

Atlantic sturgeon are among one of the oldest fish in the world. (Photo from University of Maryland Horn Point Laboratory)

Today they are commercially extinct in the region and can only be caught in the northern parts of the North Sea. The reason was probably extensive fisheries well before the modern era. Statistics show substantial catches by 1875 declining rapidly in the last quarter of the century to nil around 1910.

It would seem that the southern North Sea haddock stocks were wiped out by the intensive fisheries of the German and Danish sailing fleet. Similarly, sturgeon used to be landed in thousands per year at the Hamburg fish auction. They were almost extinct already before the First World War.

So what? We are still able to buy cheap tuna and codfish. What we do not see is that the ocean is much poorer than it used to be. We have taken out the big fish which used to provide us with delicious dishes. The small fish which dominate the market today are worth much less in economic terms than the big fish. Even worse, the ecosystem depends on the big fish. The eggs of a mature cod is more resilient – has a larger chance of survival – than the first spawn of a young cod. The large fish are needed to ensure a structured and therefore more resilient ecosystem – much like the elephants, lions and giraffes ensure a rich ecosystem in the Savannah. When we lose the big ones, smaller species often of low commercial value to us take over.

Humans have not only impacted the North Sea at the upper trophic level (comment by the editor: The trophic level of an organism describes it’s position within the food chain). In the eighteenth century the market for European oyster developed rapidly and gave rise to a considerable extractive industry. The nearshore oyster beds were fully exploited by the nineteenth century, and by the early twentieth century oyster beds were showing clear signs of overexploitation. Estuary pollution was a problem but the overriding problem seems to have been that the oyster was unable to reproduce at the pace needed. The German and Danish oyster beds in the Waddensea went extinct while fisheries in England and other parts of Denmark were much reduced. Only thanks to the introduction of mariculture production sites in France did the European oyster production keep up with increasing consumer demands.

All is not doom and gloom: few big fish have gone extinct yet. History shows that moratoria on fishing sometimes work. After the Second World War when fishing came to a halt, ocean life rebuilt. When the EU banned herring fishery in the 1970’s, the stock built up in ten years. The lesson seems to be that long-term concerted action works. The challenge is that the ocean is large and unregulated, and declines have been steep. When we ask where are the big fish, the answer is simple: we ate them. We need good global governance of the sea now, or we shall soon no longer have any big fish.

Featured image credit: USFWS Image

Poul Holm
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