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The value and role of otter re-introductions and releases has been extensively debated by those involved in otter conservation (Mason, 1992; Jefferies, Wayre & Shuter, 2000; Green, 1997). Those supporting re-introductions and those opposing them felt that they had the best interests of the otter at heart. More recently re-introductions have become a point of debate in the angling press (Daily Mail, 2010; Stones, 2010) fuelled largely by erroneous assumptions that re-introductions are continuing and are causing an artificial increase in otter populations.

The first Otter Survey of England in 1977-79 showed that in the previous 20 years otters had declined from being a widely distributed animal, ‘supporting’ 13 otter hunts in England and Wales, to remnant populations only in the south west, in some areas next to the Welsh border, in parts of the north of England and in north Norfolk. Over most of England the otter was already extinct and it seemed likely that if action was not taken the otter would become extinct in the whole of England. Two re-introduction programmes were therefore set up which between them released a total of about 170 otters. The Otter Trust released 116 captive-bred otters, starting in 1983 and concluding with the release of 17 otters, at three locations in the upper Thames catchment, in 1999. The Vincent Wildlife Trust released 49 rehabilitated otters (largely orphaned otter cubs), mainly in Yorkshire, between 1990 and 1996. Most of the re-introductions were in Anglian Region, at least 99 between 1983 and 1998, with 29 in Yorkshire region, 23 in Thames and small numbers in South West, Wessex and Southern regions and two each in the lower Trent and Wye catchments

The re-introductions in England largely reinforced existing otter populations (Green, 1997). Remnants of the original otter population were usually present in the areas where releases were undertaken, though usually in low or very low numbers. In England most releases consisted of 2-4 otters (Jefferies et al., 2000; Green, 1997) which would have created very small populations vulnerable to chance losses except in those areas close to an existing

population (whether remnant or caused by releases) or where such populations were reinforced by subsequent releases.

In Anglian Region the results of the 1977-79 Otter Survey of England (Lenton et al., 1980) showed that otters were present at that date with the main concentration being in north Norfolk. The population there suffered a major decline between 1978 and 1986 (Strachan et al., 1990; Spalton & Cripps, 1989) and it is likely that the Otter Trust re-introduction programme prevented the extinction of otters in Anglian Region. The main increases in otter activity in the region between 1994 and 2002 were in those areas where introductions took place between the two surveys indicating that a viable population had probably not been achieved before about 2000 (Strachan & Jefferies, 1996; Crawford, 2003). It is likely that the Otter Trust programme of releases speeded up the re-colonisation of Anglian Region by around 20 years.

In Yorkshire the Vincent Wildlife Trust release programme between 1990 and 1996 strengthened the existing very low otter population. However the population remained small even in 2000. There was an increase between 1992 and 2000 but it was only from 11 to 19 per cent of positive sites. It is likely therefore that the introductions supported the otter population in Yorkshire and may even have helped it achieve the critical mass

required for expansion. The results of the present survey show a major increase in positive sites but this increase is mainly concentrated in the northern part of the region near the expanding population of Northumbria. It is therefore likely that natural re-

colonisation has been the main factor in Yorkshire although it is likely that re-introductions speeded up the development of a viable population by some years.

In Thames Region, otters had started to re-colonise the west of the catchment,

presumably having crossed the watershed from rivers in Wessex region, prior to 1992 (Strachan & Jefferies, 1996; G. Scholey, pers. comm.). Presumably this natural re-

colonisation would have continued and the Thames would have been colonised naturally. However the introductions led to a significant increase in otter activity and must have speeded up re-colonisation by some years.

It is impossible to know what would have happened without the introductions or what impact they had. It is also difficult to determine survival rates following release although some released otters were fitted with radio harnesses and the later releases were all fitted with microtransponders. Between five and seven per cent of released individuals are known to have died soon after release (Green, 1997), but this depends upon members of the public finding and reporting the corpses and must be a serious underestimate. In Anglian Region the level of introductions was probably sufficient, together with the very small remnant population, to have enabled a breeding population to develop. In Yorkshire the combination of the remnant population, introduced otters and animals naturally re- colonising from the north enabled a breeding population to develop although it is not possible to discover what role each of these factors played. In Thames otters would have re-colonised naturally but the releases probably speeded up the process. The releases in other catchments were all very small scale and were mainly in areas into which otters were already spreading. They may have had a small impact but this is very unlikely to be

significant at a population level.

The second and third otter surveys of England (1984-86 and 1991-94) showed that otter populations, although still very fragile, were starting to recover and by the mid 1990s it was becoming apparent that further releases were not required. In 1999 the final release by the Otter Trust of 17 otters at three locations in the upper Thames catchment including one location near a fish farm and carp fishery, brought to national prominence the possible

conflict between a returning otter population and certain sensitive fisheries such as specialist carp fisheries and trout farms. The Otter Trust had already decided, in agreement with the Otter BAP steering group, to phase out its breeding and release programme and the Vincent Wildlife Trust had already stopped its otter rehabilitation and release programme.

It is significant that the areas where otters have reached, or are close to reaching, carrying capacity had no or very few otter introductions. No otters were introduced into the South West, Northumbria or Cumbria (although in Northumbria two orphaned otter cubs were released at the point they were found and some similar releases have been undertaken in South West). Only in Wessex did introductions take place with two otters being introduced onto the Hampshire Avon in 1989 (Jefferies et al., 2000).

The only otters released since 1999 have been orphaned otter cubs and sick and injured otters, released by the RSPCA and other animal welfare organisations. The RSPCA and most of the other organisations have agreed only to release otters at the locations at which they were originally found. This is to allow otter cubs, which are released at the age they would leave their mother, to behave like ‘normal’ dispersing sub-adults and for adult otters to re-establish themselves in their previous territory - although in practice most adults which can be caught are too sick or injured to survive. Between 2000 and 2009 a total of 56 otters is known to have been released in England and Wales, mainly by the RSPCA (A. Grogan, pers. comm.). As would be expected these have nearly all come from areas with higher otter populations. Returning these animals to these same areas will therefore have little or no influence on population levels. The level of otter releases since 1999 should be compared to the 1,080 otters (nearly 20 times as many) which were killed on the roads in England and Wales and handed in to the Environment Agency for post-mortem within the same period (Chadwick & Sherrard-Smith 2008; Chadwick & Deakin 2009; E. Chadwick, pers. comm.). These otters are of course mainly from the same areas as the releases and in some cases may well include the mothers of the orphaned cubs. The figure for otter road kills must significantly underestimate the total death rate from this cause as it is known that many otters which are found are never handed in to the Environment Agency and others will not be found at all.

The release of cubs as sub-adults at the location where they were found is not without controversy. Otter cubs normally remain with their mother for 12 months learning how to survive in and exploit their environment and it is obviously impossible to mimic this

effectively in captivity. Since 1999 there have sometimes been suggestions that orphaned cubs should be released in areas where otters are less common. Simpson (2010)

expressed concern that released otter cubs were less able to survive in the wild than cubs which have remained with their mother and suggested that it would be best to release these otters in south east England where there are few if any otters. However the general consensus within otter conservation is that this could seriously damage relationships between angling groups and otter conservation and for that reason it is best to continue with the present release protocol (G. Scholey, pers. comm.). Otters like all species have to survive within a largely man-created environment and the possible small benefits gained by otter populations as a result of releases away from the home area would be more than outweighed by the antagonism this would be certain to produce.

When considering the possible impact of introduced otters it should be noted that less than 230 individuals of this native species are known ever to have been released in England and Wales. In contrast, in 2009 alone, fishery owners and managers applied to the Environment Agency for consent to introduce 13.6 million fish into waters in England and

Wales (C. Eade, pers. comm.) although not all of these will actually have been introduced. Many of these will be of non-native species.