The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
The original range included the whole of the Palaearctic into Indo-Malaya, from Ireland to Kamchatka and Norway to Java. However, Otter has declined or disappeared from parts of its European range. It has become extinct in Laos and Malaysia, with an unknown status in other parts of Asia. Otter occurs throughout Ireland (Harris & Yalden, 2008) and Great Britain with good populations in Scotland, Wales and south-west England. The latest survey data from the Environment Agency (Crawford, 2003) shows that Otter is more widespread, and now recorded in all counties (although they are not believed to be breeding in Surrey). The early 1990s population estimate is 7500 animals: 350 in England, 6600 in Scotland and 400 in Wales (Macdonald and Tattersall, 2001). The British Otter population is internationally important, especially in the south-west.
Comprehensively distributed throughout Cornwall and found on all catchments: Cornwall is probably now at carrying capacity. Exeter University, aided by the Environment Agency and Cornwall Wildlife Trust volunteers, carried out the first DNA study of Otter in Cornwall on the River Camel SAC to estimate population numbers. Eighteen otters were identified over two years (A. Pountney, pers. comm.) [Final PhD report due end of 2008]. In the last eight years they have been regularly seen at a number of hotspots including Bude, St Austell, Truro, St. Ives, between Wadebridge and Bodmin, and in the Luxulyan Valley. Areas with few or no Otter records circa 10 years ago, such as The Lizard, Land' s End and the Red River, now have good numbers of records. There are occasional reports of Otter on the Isles of Scilly (sightings and spraint), but these are unconfirmed and thought to be highly unlikely (Kate Stokes, pers. comm.). The Fourth Otter Survey of England 2000-2002 (Crawford, 2003) confirms that the south-west is still the stronghold for Otter in England: in England 36% of the survey sites were positive for Otter, in the south-west this figure was 83% (though this is thought to be low as the surveys were undertaken mainly during floods when signs of Otter are hard to find (Kate Stokes, pers. comm., 2008). The fifth survey is overdue, but should be carried out in 2009 by the Environment Agency (A. Crawford, pers. comm.).
Habitat & Ecology
A well studied species with a wealth of reference material available and in recent years (2005-2008) there have been at least four university student-projects regarding Otter in Cornwall. Found in lakes, rivers, streams, marshes, moorland and in coastal areas, Otter will make overland journeys from one watershed to another and may alternate between marine and freshwater habitats. Sometimes seen in the sea, their signs are occasionally found on beaches. The availability of suitable breeding and lying up places is important and may influence distribution (Corbet & Harris, 1996). Otters are opportunist feeders with a wide ranging diet which consists mainly of fish (especially slow-moving species such as eels); amphibians, birds and mammals are also taken (Corbet & Harris, 1996; Chanin, 1988; Harris & Yalden, 2008). Stomach contents from otters examined by the WVIC found eels to be the main prey item. Frogs and salmonids were also important but bird and mammal remains were rarely found (Vic Simpson, pers. comm., 2008). From the hundreds of spraints that Kate Stokes (CWT) has looked at, their diet in Cornwall is predominately fish and amphibians.
Being relatively short-lived, Otters have to sustain their populations by producing enough young during their short life span. Hence anything that unnaturally affects their breeding success can quickly affect the survival of populations (Harris et al ., 1995). Other threats include disturbance, habitat destruction, pesticide use and other pollution (Morris, 1993), persecution, road accidents and diseases (Strachan & Jefferies, 1996). The effect of pollution has serious implications in terms of destroying fish as well as possible direct lethal/sublethal effects on Otters (Strachan & Jefferies, 1996). There is not any evidence, however, to support claims that habitat destruction, persecution or diseases have ever been a threat to the Otter population in Cornwall. There is also no evidence of ill health in this species caused directly by heavy metals (Vic Simpson, pers comm, 2008). Vic and his WVIC team have examined over 680 dead Otters of which 190 were found in Cornwall. Of these the commonest cause of death was due to roa
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.