SCIENCE / Natural home - or ring of blighted water?: Otters are being returned to our rivers. But is this merely condemning them to death in a polluted environment? Gail Vines reports

IN JANUARY this year, a young adult male otter was found dead near the centre of Bishop's Stortford, a busy market town in Hertfordshire. A local vet, Frederick McKeating, performed the autopsy. From its injuries - smashed skull, broken ribs and severe internal bleeding - McKeating says it seems the animal was hit by a car.

On the face of it, this was just another sad case of a wild animal meeting its end on the road. Nothing strange about that - motorists in Britain kill thousands of animals each year. The otter was probably hit while crossing a road near the river Stort, about 100 yards from McKeating's surgery in the town.

Yet there is something unusual about this casualty. The last wild otters to inhabit the river died in the 1950s, apparently the victims of pesticide poisoning. Today, otters survive only in the north and west of Britain - with small, scattered populations in East Anglia. So what was an otter doing in Bishop's Stortford in the first place?

The answer is that otter enthusiasts released the young male and two females near the town late last year, in the hope that they would thrive, reproduce and re-colonise the habitat. It is part of a 'reintroduction programme' set up by Philip Wayre, director of the Otter Trust, a registered charity based at Earsham in Norfolk, just by the Suffolk border. Wayre breeds captive otters at the trust's various private zoos open to the public, and then looks for landowners who are happy for otters to be released on their rivers.

Such landowners are not difficult to find these days. Many commercial concerns are keen to be seen to do good works for conservation, and otters make marvellous PR. The first of the latest releases, of three otters on gravel pits at Amwell in Hertfordshire, were carried out by the St Albans Sand and Gravel Company. It was part of the 'restoration of our quarries as a conservation / wildlife area', according to John Spruell of the company. Releasing otters into an ideal habitat was, he says, a natural extension of the firm's conservation work.

In the second release last winter, Philip Wayre set free another trio of captive-bred otters into the river Stort in Essex. The co-operating landowner on that occasion owns a restaurant next to a marina along a stretch of the Stort that looks more like a canal than a river.

Wayre says: 'There is absolutely no doubt that the reintroduction programme is proving highly successful.' Since 1983, the trust has bred and released 43 otters in various parts of England. Many are alive and from these there have been 26 successful known breedings, he says. The trust plans to release about a dozen more otters each year.

Wayre targets areas where there aren't any wild otters, to avoid interfering with natural populations. 'The latest surveys show that otters are increasing west of a line from Manchester to Lyme Bay,' he says. 'We do not release any west of that line. East of it, there isn't any otter population worth talking about.' His philosophy is simple: 'It doesn't do any harm to give them a boost, and it may well do some good.'

But Frederick McKeating thinks it is wrong to set otters loose in one of the most densely populated parts of South-east England: 'It's like letting a five-year-old play on the motorway. It's totally foolhardy.'

McKeating reckons that the river is too sick to support otters. The Stort runs past Stansted airport, and last year was severely polluted by leaking aviation fuel. But although the Protection of Animals Act makes it illegal to abandon domesticated animals, there are no legal restrictions on releasing any native British species into the wild.

Yet the male otter's autopsy results support McKeating's feeling that the Stort is not ready for otters. 'The otter had very little body fat and its stomach and intestine were completely empty, indicating that it hadn't fed for some time.' McKeating, who fishes in his spare time, says that stocks in the river are poor.

Looking for further clues to the otter's physical condition, McKeating contacted Chris Mason, an otter specialist at the University of Essex. Mason suggested he send samples of the otter's internal organs to be analysed. The lab results showed high levels of pesticides and other persistent pollutants known as PCBs. Dr Mason said PCB readings were more than double what some researchers consider safe background levels.

A female otter has also been found dead near Royston, says Melanie Findlay of the Hertfordshire and Middlesex Wildlife Trust. This may mean that only four of the six otters recently released have survived.

About the losses, Philip Wayre says: 'We do not expect all our released otters to survive . . . there are bound to be failures.' Not all otters born in the wild would survive, he points out. He argues that releasing otters can do no harm to the wild population, as there isn't one - and it might do some good. 'If we release four otters and they all die, we're very sorry; perhaps we shouldn't have done it. But so what? We'll soon be releasing another six.'

Dr Chris Mason is a persistent critic of Wayre's reintroductions. As a senior lecturer in biology at the University of Essex, and a member of the otter specialist group set up by the International Union for Conservation of Nature and Natural Resources (IUCN), he particularly objects to Wayre's latest releases.

'In terms of animal welfare, it seems unfair to chuck an animal into a river like the Stort,' he says. North of Bishop's Stortford, the river soon runs dry due to droughts and agricultural extractions. Otters travelling south would join the Lea system that feeds into the Thames, taking them into the East End of London.

Mason is also worried about the quality of the river's water. Even in its best stretches, the Stort may be so contaminated by agricultural and industrial pollutants as to be a threat to otters. As fish-eating carnivores, they are particularly vulnerable to pollutants that become concentrated in the aquatic food chain.

To monitor the health of free-living otters, Mason and his colleague Sheila Macdonald have been analysing the otters' droppings, or spraints. They have found high levels of organochlorine pesticides - dieldrin, lindane and DDE (a breakdown product of DDT) - as well as PCBs.

Chris Mason argues that levels of PCBs in spraints on the Stort are three times higher than some environmentalists consider safe. The liver fat of the male killed in Bishop's Stortford had PCBs at 24.7 milligrams per kilogram, he says. 'This is getting close to our level of concern, especially for an animal that has been in the wild only a month or so.'

But another distinguished researcher who supports Wayre thinks PCBs are nothing to worry about. Don Jeffries, in charge of research into vertebrates and terrestrial pollution at the Joint Nature Conservation Committee in Peterborough, says: 'In the West of England otters are recovering, even in areas where PCBs remain high.' He thinks otters in South-east England were originally killed by the pesticide dieldrin. This pesticide is now banned, and seems to be gradually disappearing from the natural environment.

Convinced that pollutants are not a hazard, Jeffries is less bothered by possible shortcomings of the latest release sites. 'I wouldn't have put them in the Stort in the Hertfordshire area myself,' he says, 'but it's up to Philip Wayre. If you don't try, you can't succeed.' Wayre himself is convinced that his reintroductions are unfairly questioned.

Short of putting a job-lot of otters in cages and dosing them with toxic chemicals, there is no way of quickly settling the disagreement about which pollutants most harm otters. Meanwhile, conservationists working for local wildlife trusts and the National Rivers Authority play pig in the middle. No one wants to antagonise Philip Wayre, nor to appear to obstruct his innovative and ambitious scheme to get otters back into South-east England. But these conservationists are worried too that all may not be well with the rivers.

Chris Miles, conservation officer for the Essex Wildlife Trust, does not support the reintroductions. 'We'd love to have them back,' he says, 'but we do not believe that releasing otters in Essex is supportable. Essex rivers are far too polluted.' And he points to another danger: 'It gives the misleading idea that our rivers are healthier than they are, because otters are there. They should be the litmus paper for our rivers. If the habitat is right, the animals will come back on their own.'

Melanie Findlay, otter habitat project officer for the Hertfordshire and Middlesex Wildlife Trust, is also concerned about the project. She says diplomatically: 'We need to do lots of research before we release any otters. In Hertfordshire, there are quite a few risks to them.' While stressing that her group is 'trying to maintain good relations', she makes it clear that the wildlife trust 'didn't want the releases to go ahead unless adequate research was done beforehand - and in my view it wasn't'.

Findlay points to the research just started by the Thames Region of the National Rivers Authority. Alastair Driver, conservation manager for the authority, is now sampling fish from selected rivers for heavy metals and pesticides. The aim is to 'enable us to determine whether otters can survive and breed in the region'. The authority is also planting trees and shrubs along riverbanks to give otters the cover they need. 'We hope otters will colonise our region naturally if we improve the habitat,' Driver explains.

Philip Wayre argues that there is little point in analysing fish for heavy metals and pesticides, since 'nobody knows what levels of any particular pollutant will adversely affect otters'. Waiting for the results, he says, 'would cause unnecessary delay' in reintroducing them into the wild.

But Wayre has yet to convince all his critics. Hans Kruuk, head of the otter research unit at the Institute of Terrestrial Ecology's field station at Banchory in Scotland, says: 'In principle, it is not a responsible thing to do - to release animals when we don't know the reasons for their original disappearance. It is very tough on the animals being released.'