Should we worry about the number of fish slaughtered on the intakes of nuclear power stations? Peter Henderson’s estimates of the impact rely on calculating how many of these fish would have survived to adulthood had they not been broiled. The numbers are large – thousands of tonnes of some species. But while the loss of juvenile fish had little effect on adult stocks in the 19th century, today’s stocks are close to record lows. Best estimates suggest there are 30 to 50 times fewer cod around today, 100 times fewer “common” skate and 20 times fewer turbot. Many species have experienced similar declines because of human impacts, the main one overfishing.

Against this background, losses of juvenile fish take on new significance. In some estuaries and coasts, the power industry may cause significant losses to the fishing industry, and could hold back the recovery of falling stocks. The freshwater eel, for example, has over the past 30 years suffered a Europe-wide 99 per cent drop in juveniles heading up-river from the sea. The reasons include habitat loss and possibly climate change. For its young, power stations could mean the last straw.

Unlike mammals, which invest a great deal of energy in raising a few offspring, fish invest a very small amount of energy in each of hundreds of thousands, to millions, of eggs. Most species abandon them to the whims of ocean currents and never see their young again. Alexandre Dumas said that if all of the offspring produced by a cod were to survive, and their offspring also survived, within a few years it would be possible to walk across the Atlantic dryshod upon their backs. But the seas have never filled with fish like this, because most fish die young. Fishery scientists joke that the average lifespan of a fish is about half an hour. It isn’t quite that fleeting, but life is brief.

Callum Roberts is Professor of Marine Conservation at the University of York and author of The Unnatural History of the Sea: The Past and Future of Humanity and Fishing (Gaia Books £7.99).

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