As part of a scheme to monitor the distribution of otters throughout the UK, four England otter survey have been carried out covering the years 1977-79, 1984-85 and 1991-94, and 2000-02. Sites were selected by accessibility and likelihood of finding signs of otter activity - typically road bridges and the confluences of watercourses. The number of spraints and presence of mink was also recorded.
More information on this dataset can be found in the Freshwater Metadatabase - BF_GBIF_13 (http://www.freshwatermetadata.eu/metadb/bf_mdb_view.php?entryID=BF_GBIF_13).