Scottish Natural Heritage

BIODIVERSITY INDICATOR S012 - 2004

Status of otters in freshwater habitats The otter is a widespread aquatic mammal. It is mainly carnivorous, feeding on a range of aquatic vertebrates and invertebrates and occurs in a range of terrestrial habitats including the coast. Otters rely upon good quality fresh water and have in the past been excluded from much of the central Lowlands of due to the pollution of their watercourses. Their reoccupation is confirmation of improved environmental conditions and restored ecological quality.

Otter ©SNH Images Evidence Survey data on otters were collected by the Vincent Wildlife Trust (VWT) up to 1994, and more recently by Scottish Natural Heritage (SNH). The most recent data are from the fourth national survey of otters in Scotland. A total of 1,376 survey sites within 574 different 10km-squares were surveyed over a two year period, 2003-2004. Positive sites are recorded as sites which show presence of otter droppings (spraints).

Change in occupied sites for otters, 1979-2004 Vincent Wildlife Trust

100

90 80 70

60 50 40

30 20 Percentage Positive of Sites 10

0 1979 1984 1991 2004 Year Assessment  Occupied sites rose from 57% of Scotland in 1979 to 92% in 2004.  The largest increases were in Forth & Borders (17% in 1979 to 87% in 2004) and & Ayrshire (24% to 83%). Increases also occurred in East , , & and & .  , Western Isles, North Highland, West Highland and Dumfries & Galloway, at 96% occupancy, are presumed close to carrying capacity.

TREND Increased DATA CONFIDENCE High

http://www.snh.gov.uk/indicators/

Commentary Otters are now near-ubiquitous in Scotland, occupying sites in urban and highly disturbed waterways. Some 1,267 sites (92%) and 568 10km squares were recorded as positive. This compares to 57% of sites in 1977-1979, 65% in 1984-1985 and 88% in 1991-1994.

The population size cannot be estimated from spraint / sign surveys. The protocol for surveying in the past has stated that searching for spraints stops when spraints are found or when a distance of 600m has been searched. Consequently, different distances were investigated for different sites and so direct comparison cannot be made between sites (Strachan, 2006).

Source data and updates Survey data up to 1994 were collected by the Vincent Wildlife Trust (VWT) and made available to Scottish Natural Heritage (SNH) in 2002. Three VWT surveys were undertaken in 1977-79, 1984-85 and 1991-94. From 2003 onwards, the data have been collected by SNH, from site condition monitoring on 44 Special Areas of Conservation (SAC) and one SSSI. The data comprise presence/absence information at sample sites in both freshwater and coastal localities across the country (Strachan 2006).

Updates will be available every 6 years.

UK Indicators There is no equivalent for this indicator at the UK level.

References Green, R. & Green, J. 1980. Otter Survey of Scotland: 1977-79. Vincent Wildlife Trust, London. Green, R. & Green, J. 1987. Otter Survey of Scotland: 1984-85. Vincent Wildlife Trust, London. Green, R. & Green, J. 1997. Otter Survey of Scotland: 1991-94. Vincent Wildlife Trust, London. Strachan, R. 2006. National survey of otter Lutra lutra distribution in Scotland 2003-2004. Scottish Natural Heritage Commissioned Report F03AC309.

http://www.snh.gov.uk/publications-data-and-research/trends/scotlands-indicators/