The Environment Agency (EA) is to ban the century-old angling practice of boosting failing populations of wild brown trout with farm-reared specimens capable of breeding with them. While the move is likely to have little visible impact on day-to-day trout fishing, it could, with other actions taken recently, increase the chances of this fabulous and widely threatened sporting fish being able to survive in the wild.

The EA has taken the decision, it says, because of mounting evidence that breeding between farmed and wild fish produces offspring less able to cope with life in rivers and lakes. While the adverse impact appears variable and often small, scientists say, it is cumulative over time. It is this long-term threat that prompted the move.

Stocking with farm-bred trout began more than 100 years ago, when little was known about genetics and hence few cared whether or not stock fish could breed in the wild. Countless fish have since been put into rivers and lakes to improve anglers’ sport. Today, trout fishing is so popular that close on a million trout a year need to be stocked in England and Wales alone to make it possible. It is the sheer scale of this input that has led to calls for new stocking rules, even among many anglers.

From 2015, the EA says, only two kinds of brown trout may be placed in waters where spawning is possible: sterile fish that cannot alter the gene pool and the offspring of wild fish taken from the waters into which their young will be introduced. Breeding between resident fish and the latter will occur, but without impact on the natural stock.

Most farm fish, selectively bred, have been reared to do well in the undemanding conditions of captivity - and to grow rapidly. It is a process that has reduced the vigour that their ancestors possessed and wild fishes’ ability, acquired over thousands of years, to adapt to varied conditions. However, an EA spokesman said: “Our wild trout populations are [still] likely to be genetically diverse, despite many years of stocking, so we have plenty worth protecting and enhancing.”

The decision to take a more cautious approach to stocking is one favoured by most fisheries scientists and by many conservation bodies, including the Wild Trout Trust (WTT), the organisation founded 11 years ago to conserve this iconic species. However, not everyone is happy about the new rules. Some of those consulted on the changes questioned fundamental aspects of the EA’s position, from how a wild trout could be defined after years of interbreeding, to interpretation of the scientific evidence.

Other concerns have been voiced about the impact that even sterile fish could have; about whether, because they do not breed and so stay active for the whole year – an unnatural ability - they could not adversely effect wild fish in unforeseen ways. Some of the strongest opposition to the EA’s proposals has come from river owners in the South, where large fish are often stocked at high densities to attract anglers willing to pay premium rates. In response, the EA says that the evidence suggests that sterile fish are safe and that a precautionary approach to anything that could affect the future of Salmo trutta has to be right.

One block to earlier changes to stocking practice has been the ability of the fish farming industry to produce sterile fish of a quality and in a quantity sufficient to meet anglers’ needs. Now the science is available and a timetable has been set to enable breeders and fishery owners to gear up. The plan is that 30 per cent fewer fertile trout will be stocked in English and Welsh rivers by 2010, that 50 per cent fewer will be stocked by 2013 and that no fertile fish will be stocked from 2015.

Wild trout have long been in decline. Heavy industrial pollution killed off many populations in the first half of the 20th century. Changing industrial processes and house-building programmes have increased the demand for water, shrinking the rivers and lakes in which the wild fish live. Decades of habitat neglect have resulted in silt choking the gravels in which wild fish spawn, fertilisers used in intensive farming have prompted suffocating growths of water algae and insecticides used on crops are prime suspects in the collapse of the aquatic fly-life that fish feed on.

Now, many will hope, the corner is being turned. Salmo trutta was recently included in the Government’s Biodiversity Action Plan as deserving special study. The EA has been putting more money into habitat improvement. The WTT has been launching about 50 river improvement projects a year in Britain and Ireland and is expanding to launch more. Legislation emanating from Brussels should improve water quality over the next few years. Now, any farmed genes in the wild population look set to disappear.

Many anglers will find back-room developments such as these remote from the simple pleasures of casting a fly to a trout. But they are important steps and anglers should take note. Without them, there could eventually be little to cast to.

Brian Clarke’s fishing column appears on the first Monday of each month

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