The nuclear industry in Britain is killing billions of fish every year and taking a devastating toll of stocks, an Oxford University academic suggests.

The impact can be so severe in the worst-affected regions of the seas around Britain that death rates are equivalent to half the commercial catch for some species.

Coastal power plants that have cooling systems that extract water from the sea are to blame for the destruction, according to Peter Henderson, an environmental researcher. Figures he has compiled suggest that the damage to fish stocks is much more severe than records have indicated previously. He calculated that had the young fish killed in power stations survived they would have added thousands of tonnes of fish annually to Britain’s stocks.

With a new generation of nuclear power stations likely to be built over the next 20 years the threat posed to fish stocks needed to be addressed urgently, he said. The net impact on fish populations was poorly understood because too few studies had been carried out.

Dr Henderson is concerned that too little account is taken of the impact on fish stocks of the deaths of many billions of eggs and young caused by coastal power plants, both nuclear and conventional.

The number, weight and species of fish and crustaceans removed from filters at power plants can be measured accurately, but it is much harder to assess the impact of the deaths of eggs, larvae and small fish.

“The number of animals killed is colossal,” Dr Henderson, an associate lecturer at the University of Oxford and director of the Pisces Conservation environmental consultancy, said. “Very small fish get sucked in in very large numbers.”

The impact on populations is compounded by the loss of prawns and shrimps which, like young fish and eggs, form an important part of the diet of larger animals. At Dungeness nuclear power station at Romney Marsh, Kent, where huge numbers of sprats are known to form shoals, the outfall pipes have been known to become clogged with dead fish. “We are talking as many as 250 million fish in as little as five hours,” Dr Henderson said.

In the southern region of the North Sea it was calculated that the mortality of eggs and young was so high for sole that it had been equal to 46 per cent of commercial fishing. Similarly, herring mortality off parts of the East Coast was 50 per cent of commercial landings.

Dr Henderson also identified the English Channel as a badly affected region because of the number of nuclear power stations on the coast on both sides of the Channel. Coal-fired stations and other installations such as those in the petrochemical industry present similar problems, but nuclear plants are among the biggest extractors of water.

Water is pumped from the seas in vast quantities, with British nuclear plants extracting at up to 60 cubic metres (2,100 cubic ft) per second. The Gravelines plant on the French north coast pumps at up to 120 cubic metres per second.

Once the water has been used to cool the reactors it is pumped back into the sea where, having been warmed up, it attracts a variety of marine creatures, many of which get caught up in the intake systems and killed. Fish that are too young or too small to be caught by the 1cm mesh screens – especially pipe fish and eels – travel through them, as do eggs and larvae, and pass into the reactors’ cooling pipes. Many die after being heated to 30C (86F), chlorinated and given small doses of radiation.

The toll of fish stocks can be avoided at new nuclear plants with the introduction of dry-cooling, said Dr Henderson, who called for this method to be adopted, despite the higher costs, if another generation of nuclear power plants is built.

Callum Roberts, Professor of Marine Conservation at the University of York, said that the report, which had not been subjected to peer review, raised serious questions about the role of nuclear and other power stations in damaging fish stocks. “I think it’s interesting that the quantity taken by the power stations is large, especially if you look at the possible cost in the future [of] prematurely killing these fish,” he said.

“It has become more significant over the years because of the decline of inshore stocks and, indeed, of the decline of some species going so far that they are reaching the status of becoming endangered, like the eel. We have to look at this problem.”

The Centre for Environment, Fisheries and Aquaculture Science has been commissioned recently to carry out an environmental survey of the waters near where four new nuclear plants are expected to be proposed. British Energy commissioned the survey to check which fish and other marine animals were found around Sizewell, Dungeness, Hinkley Point and Bradwell. Researchers will attempt to establish the quantity of fish in the four areas, how nuclear plants have affected them in the past and what impact could be expected if new power stations were built there.

“All of these sites are suitable for new nuclear power stations,” said Sue Fletcher, of British Energy, who maintained that the industry would “strongly contest” any suggestion that unsustainable quantities of fish were killed in cooling systems. A spokesman for Magnox, the operator of a coastal nuclear plant at Wylfa on the Isle of Anglesey, said that the group undertook “extensive monitoring activities”.

Emily Lewis-Brown, a marine campaigner for WWF, the wildlife charity, said it was concerned that coastal power stations represented a frequently overlooked, additional burden on British fish populations. “There is evidence to suggest that when power stations stop killing fish, local populations start doing better,” she said.

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