RING OF BRIGHTER WATER

Clean rivers and conservation measures are helping one of Britain's favourite wild animals reclaim its old haunts. New research tracks the 'rolling otter front' as it moves eastward

In a hidden valley among the hills which feed water into the Thames west of Oxford, there is a fast-flowing ribbon of river. Next to one of its twists, overlooking a deeper pool, is what looks like large newly- built bonfire, surrounded by a cluster of saplings - oak, ash, hawthorne, bramble and guelder rose. In a few years' time when the saplings have grown, the pile of sticks will be scarcely visible amidst the surrounding greenery - a fine and private place for an otter to make its home.

The last recorded breeding of native wild otters in the upper Thames valley was in 1975. Afterwards, as in most other valleys in lowland Britain, the otter became locally extinct. Then, three or four years ago, signs began to appear that otters had returned to the Thames and its tributaries. There were "uncorroborated" sightings, footprints in soft mud, spraints - musky otter dung, smelling faintly of jasmine tea - found on stones or near bridges. A dead otter was found on the M4 motorway near Maidenhead. The animals were passing through - but why were they not stopping?

The answer helps to explain why a rare modern conservation success story - the rebuilding of otter populations after their crash in the 1960s - is far from over. With the chief known threats to the otter - hunting, persecution and organochlorine pesticides - largely removed, Britain's biggest and most popular carnivore is moving back into its old haunts. The recolonisation is from west to east, with the animals spreading out from their surviving strongholds in Wales and the West Country using their own version of the motorway network - the catchments of rivers like the Severn and the Avon. Don Jefferies, one of Britain's foremost experts on the otter and the author of a forthcoming report on its recovery, published by Vincent Wildlife Trust, describes this as a "rolling (otter) front" - but it is progressing remarkably slowly.

Radio-tracking of otters has shown that males especially travel long distances, swimming over 14kms in a single night and covering, in the case of one animal measured, 42kms by land and water in 24 hours. The epic journeys of Henry Williamson's fictional Tarka, from coast to moorland and back again - over 100kms - in a few days are thus closer to reality than researchers once believed. Jefferies calculates an otter could in theory get from otter-rich Devon to virtually otter-free Kent in just over a fortnight. But the otter "front" - the recolonisation of habitats and the establishment of territories and breeding groups - is moving at only 3.6 kms a year. At current rates, it will be 112 years - 2108 - before the otter returns to anything like its pre-industrial population levels.

For conservationists, there are several lessons to be drawn from this extreme statistic. First, it is very easy to wipe out a species - otter populations crashed rapidly after the introduction of aldrin, dieldrin and heptachler as sheep-dips and cereal seed dressings in the mid-1950s - but much more difficult to rehabilitate it. The otter in particular is a slow breeder, with each female producing about two-and-a-half breeding- age cubs in her lifetime. Society was also slow to respond: the disappearance of the otter was noticed by otter hunts as early as 1957, the first voluntary ban on the "drins" was agreed in 1961 but it was not until 1981 that all use of aldrin and dieldrin was made illegal.

Second, a lot can happen in a century. The drins may have been banned and the otter hunts disbanded - it has been illegal to catch or kill otters since 1978 - but there are many new threats on the horizon. Third, we may need to change our ways considerably if we want the otters back.

One important, psychological change has already occurred - the transformation of the otter from vermin to icon. The first pack of otter hounds was recorded in the 13th century and the animal was officially designated a pest in 1566; bounties were offered for dead otters (three times the rate for a weasel) and in parts of the country hunting was made compulsory, not least to protect the well-stocked stews (fish ponds) of manor houses. But thanks to fiction, wildlife films, rarity and nostalgia, the otter's former enemies - farmers and anglers - are now among its friends.

On the tributaries of the upper Thames and Cherwell, for example, the Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust, in partnership with the Environment Agency, is trying to persuade landowners to create good otter habitat. One farmer remembers seeing otters in the valley near his house when he was a child, in the 1940s, and would like to see them again. Hence the big pile of sticks next to the river - an artificial logpile holt built by volunteers and designed to tempt a passing animal, into residence.

But otters need food and cover somewhere to lie up during the day - as well. The farmer's river has thus been made more otter-friendly. Underwater rocks create rapids or "riffles" to encourage fish spawning. Banks are fenced off to promote sedge and reed. Stakes are driven into the riverbed and then backfilled to make "berms" or mini-wetlands. There are small islands and meanders, "slow flows" and newly-planted thickets.

The BBOWT initiative is part of the Otters and Rivers Project run by the Wildlife Trusts. Launched in 1989 and now involving nearly 20 county trusts, its achievements include the building of 245 logpiles and 98 undergrounds holts and working with 1,200 landowners on over 210 habitat improvement and river restoration schemes. Annie Masson, BBOWT's project officer, says the engineering mentality with which one saw overhanging trees and bankside cover, much desired by otters, as the enemies of good river management is now giving way to a more ecologically sensitive approach. Oxfordshire, however, remains a "very neat and tidy" county, with too many river banks shaved by intensive grazing.

This may help to explain why, of all the regions surveyed by the Vincent Wildlife Trust (a separate body from the Wildlife Trusts), the Thames region showed the least sign of otters. By 1992-3, otter signs were present nationally at 23 per cent in the mid-1980s. Regionally, however, figures varied from 87 per cent in the South West and 63 per cent in Wales to 3.7 per cent in the Southern region and 1.23 per cent in Thames. Other possible explanations include lack of fish and water - some of the River Kennet's headstreams were dry when surveyed - together with the fact that relatively few captive bred or rehabilitated otters have been released in the Thames region.

The release programme, started in 1983 by the Norfolk-based Otter Trust, may have saved the otter from extinction in large areas of the country - most notably in East Anglia where the assault by pesticides was at its most intensive. Animals are "acclimatised" in pens on river banks for at least three weeks; food is provided for another 12 days after release. By the end of 1994 over 100 animals had been released, mainly in East Anglia and Yorkshire. Most have bred and some are now in their third generations. The programme has had its critics - who argue that there is little point in returning otters to rivers that remain polluted - but according to Jefferies, it represents one of the handful of captive breeding programmes to successfully return an endangered species to the wild.

In the days when otters were pests, their population ran into the tens of thousands in Britain. Last year, the number of adult otters in England was officially 3,500 in mainland Scotland and 390 in Wales. But as the otters slowly advance towards their former haunts in the south and east of the country, they will find much that has changed, and for the worse.

The land, for example, is drying out. Half of Britain's wetlands have been lost since 1945 and three quarters of ponds have gone in the last century. Human demand for water is projected to increase by up to 60 per cent, implying ever greater pressure to abstract from rivers and ground waters. Studies also suggest that climate change caused by global warming will make the western half of Britain wetter but turn the eastern half permanently more arid.

The animals also stand a much higher chance both of being caught and drowned in an eel net - such fisheries are more common in the eastern counties - and of being knocked down by cars as they re-enter the congested South-east. Road traffic is now one of the major causes of animal mortality - cars kill an estimated 47,500 badgers every year, almost a fifth of their total population - and otters are no exception. Of released otters known to have died, over half were killed on roads. For a small isolated otter population, a single black spot can make the difference between survival and extinction. At one such place, a bridge of the River Itchen in Hampshire, a special otter "underpass" has been installed to prevent further casualties.

Other solutions, apart from safer driving, include reflectors on roadside fences which scare animals from dangerous crossings. The Wildlife Trusts wants such measures made standard for new roads that might affect otters. For those who think this may be too much fuss for a furry animal, there is the most resilient of motives - human self interest. The drins and DDT have been replaced by a new range of pollutants, ranging from polychlorinated biphenls (PCBs), which are suspected of damaging the immune and reproductive systems, to oestrogen-mimicking substances that lower fertility.

The otter, as Don Jefferies points out, "swims and feeds in our drinking waters": as the top aquatic carnivore, it is a vital indicator of the health of the countryside. If the otter front rolls on successfully through Oxfordshire to Kent, it is reassurance that we can all breathe (and drink) a good deal easier. !