Samenvatting

In many countries the Eurasian otter (Lutra lutra) is extinct or numbers are declining; resulting in a classification as “near threatened” on the IUCN’s Red List. In one-third of the European countries, however, conservation efforts, enabled the return of the species or the improvement of weakened populations. A lot of conservation measures are based on inland populations, living in river systems, lakes and other bodies of freshwater. Ireland is a stronghold for the species, with Roaring Water Bay (which opens up to the Atlantic Ocean) being a core area. Little is known about differences between inland populations (which are the base of conservation measures) and such coastal populations, which may be of great importance. The goal of this study is to find out more about distribution, population makeup (density and diversity) and activity of the animals in relation to humans. Surveys were conducted every eight days, for the duration of eight weeks – to map distribution based on spraint sites and to monitor sprainting activity on 176 such sites. Freshwater (known to be a vital resource in coastal populations) was also mapped. Fresh spraints were collected for DNA analysis and camera traps were deployed to determine activity patterns and estimate population densities. Attempts to GPS tag otters were unsuccessful during this study, but a number of animals was tagged in 2010 by De Jongh et al.; providing data on home ranges. Individual ranges measured an average of 6,5km. Population estimates range from 175-219. The population was found to be distributed throughout the bay, with a preference for pools that contain freshwater. The spraint sites that were most active were also the sites that had most activity on camera, which is in line with the findings of Guter et al. (2008) who found the sprainting activity to be an indicator for visiting frequency. Individual animals were shown to move throughout the bay over great distances, as indicated by an individual that was tagged showing up on Baltimore and Sherkin Island (250m-1.9km). Another two related animals were found on Sherkin Island and Ringarogy, indicating individual movement and geneflow in the area to cover multiple islands – even if freshwater is available on either. Over 19 succesfully genotyped samples 13 individuals were found with an average observed heterozygosity of 0,585 (moderate to good). The animals are mainly active during the night, thereby mostly avoiding (not a proven causal relation, and contrary to what was found on the Shetlands) human activity in a temporal sense. Human activity is encountered by the otters in a spatial sense, with fishery and aquaculture activities, it is therefore recommended that: creels are only allowed at depths greater than 9 meters; tangle netting and trammel nets are not allowed within 250 meters of the shore (all in line with current practice); thereby safeguarding foraging grounds around the islands as well as movement corridors between them.