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The fifth national otter survey of England has for the first time achieved comprehensive coverage of the whole country. Two field survey techniques were used in parallel — full surveys for sites investigated in previous national surveys (the main survey), and spot-checks for all the alternate 50 km squares not covered in the previous surveys.
The main survey was carried out between July 2009 and March 2010. Six highly experienced otter surveyors examined 3327 sites across the country using thirty-eight 50 x 50 km squares (the north-west and south-east quarters of each 100 km square) as a sampling grid. Footprints and droppings (spraints) represent the most distinctive signs of otter and their presence within the standard 600 m survey length of river represented a 'positive' site record. Signs of otters were recorded at 1874 (56%) of sites in the main survey. In addition, the alternate squares spot-checks undertaken within the same time frame proved otter presence in 553 of the 718 10 km squares surveyed.
Direct comparison of positive records from 2940 sites used in all five national surveys reveals the recovery of otters from virtual extinction in most of England during the early 1970s. Positive site records increased from 5.8 per cent in 1977-79, to 9.6 per cent in 1984-86; 23.4 per cent in 1991-94; 36.3 per cent in 2000-02 and 58.8 per cent in 2009-10.
Recovery has continued in all but the very south-east where no signs were found in Kent or most of Sussex. Re-colonisation from strongholds in south-west and northern England and Wales has now been consolidated across much of the country and continues to drive recovery. Since 2000-02 there has been a major link-up across several river catchments. For example, there is no longer a gap in otter distribution between the south-west, south Wales, lower Wye and Severn and upper Thames. Similarly, there is now a link between populations in East Anglia, the River Trent catchment, Yorkshire and the traditional Northumbria stronghold. The pattern of recovery differs at a regional scale, with Thames showing the biggest increase in positive signs since 2000-02. In South-West Region and the River Wye catchments otter populations have probably reached a level approximating to carrying capacity, with those in Northumbria, Cumbria, Wessex andthe upper Severn close to that. Elsewhere, further recovery and consolidation will take more time.
Recovery has been in response to three main factors, the ban on pesticides that caused extinction of otters from many parts of England in the 1960s and early 1970s, legal protection for the otter since 1978, and the significant improvement in water quality in previously fishless rivers since the 1970s. Re-introduction programmes of captivebred and re—habilitated otters in certain parts of the country are likely to have speeded up the recovery locally in East Anglia, Yorkshire and the upper Thames. However the majority of the recovery has been the result of natural expansion from the remnant populations. The prospects are for full recovery across England probably within the next two decades or so. This represents a major success story for pollution control, as well as investment by the water industry and efforts by landowners and river managers to improve river and riparian habitat. Tracking the otter's recovery has demonstrated the benefits of long-term monitoring and the use of this iconic species to raise awareness of pollution problems and the benefits of action to improve the environment.