The relationship between riverbank habitat and prey availability and the distribution of otter (Lutra lutra) signs: an analysis using a geographical information system

Introduction This chapter presents preliminary findings of a research programme to determine the factors that influenced the distribution of otter signs in the upper Tyne catchment, Northumberland, England, between 1993 and 1995. The work presented here considers two aspects of the research programme. Firstly, the effect of changing the sampling scale on the pattern of distribution of otter signs in the catchment is assessed. In this context, sampling scale is defined as the size of the sampling unit. Secondly, the relationships between the distribution of otter signs and the availability of different types of riverbank vegetation and the influence of prey availability are investigated. In the majority of studies of habitat utilization by otters, the distribution of otter spraints has been used as an indicator of the presence or absence of otters (Jenkins & Burrows, 1980; Macdonald & Mason, 1983; Bas et al., 1984). A relationship between the distribution of otter signs and riverbank vegetation, in particular the availability of woodland and scrub habitats, was found in all of these studies. A similar relationship has been demonstrated using radiotelemetry techniques. Jefferies et al. (1986) showed that radio–tracked otters spent over 50% of their time in wooded areas, although only a few individuals were tracked. Green et al. (1984) showed that one of their radio–tracked otters sprainted more at centres of activity than elsewhere, although analysis of the movements of another individual showed no such relationship