Distribution, Density, Diet and Habitat Use of the Otter in Relation to Land Use in the Araglin Valley, Southern Ireland

The distribution, density, diet and habitat use of the otter (Lutra lutra) were examined in the Araglin Valley, in counties Cork, Tipperary and Waterford. Otter signs (tracks, spraints, anal secretions, holts, etc.) and environmental conditions (river depth, river width, flow regime, vegetation cover, etc.) were recorded at 112 sites across three habitat types (agriculture, moorland and forestry) in the river valley.
Three definite home range boundaries were delineated by high levels of sprainting and scraping, and results indicated the presence of six or seven otters. Significant correlations were recorded between otter signs and river depth, river width, lying-up availability and presence of holts, but no trends were found between otter signs and vegetation cover or flow velocity. A positive relationship was recorded between spraints and vegetation cover in the agriculture and moorland habitats, but a negative correlation was found in the forested sites.
Percentage frequency of occurrence, relative percentage of frequency, and percentage bulk (Sc%) were calculated for twelve food categories based on seasonal data sets. Fish (mainly salmonids and eels) were the predominant food category in each season (Sc% = 70.03). Other significant food categories included small quantities of mammals, birds, frogs and crayfish (both in February and March). Considerable variation in otter diet was revealed and was related to differences among three different habitat types and to the location of the home range. In home range 3, fish prey were relatively scarce, while birds and frogs were more important. In contrast, fish was the more important food in home ranges 1 and 2.
The trophic niche breadth of otter, evaluated using Levin's index, varied little throughout the study period, with a peak in spring/early summer and a minimum value in late autumn (October-November).