The European otter, Lutra lutra, is protected under national and international legislation due to widespread population declines across its distributional range in recent decades. Mitochondrial DNA surveys to date have revealed low diversity within the European population. In this study we examined the mitochondrial DNA diversity of the Irish population to determine the relationships between Irish and other European populations. Diversity within the Irish population was high (h = 0.75) and nine haplotypes were present, five of which were novel. This high diversity might be attributed to a combination of a number of colonisation events, and the comparatively stable demographic history of the Irish population in comparison with the rest of Europe. The haplotype network showed no clear divergence between Irish and other European populations, and possible colonisation routes of Ireland are discussed.

We present and evaluate a protocol for the capture of otters (Lutra lutra) using padded leg‐hold traps coupled with Global System for Mobile communication (GSM) trap alarms. The trapping method was highly efficient, capturing 46 otters at 6.9 trap‐nights each. Functioning alarms allowed us to remove 36 otters from their traps within 22 (SD = 14) minutes of capture. We caught 10 otters in trap sets with malfunctioning trap alarms and retrieved them the following morning, after ≤24 hours. Functioning alarms reduced the injuries suffered from an average cumulative score of 77.7 to just 5.5 on the International Organization for Standardization 10990‐5 trauma scale (Z=‐5.074, P ≤ 0.001). As a result, we strongly encourage the use of GSM trap alarms under the principle of refinement in animal experiments.

We examined the spatial structure and sociobiology of a native wild population of Eurasian otters (Lutra lutra) on mesotrophic rivers in a mild temperate climate. Radio-tracking of 20 individuals revealed exclusive intra-sexual adult home-ranges. Adult female homeranges (7.5 km, SD=1.5 km, n=7) were inversely related to river width (R 2 adj ¼ 0:68, F 6 = 13.5, P=0.014) and so appeared to be based on food resources. The aquatic area within adult male home-ranges (30.2 ha, SD=9.5 ha, n=5) was greater than that within adult female's (16.8 ha, SD= 7.0 ha) (t 10 = 2.437, P= 0.035), though this result is inconclusive because some males were tracked on oligotrophic rivers. One adult male expanded its range from 10.2 km to 19.3 km within 5 days of the death of the neighbouring male, suggesting that male home-ranges were heavily influenced by conspecifics.

Practical issues for radio-tracking studies of otters (Lutra lutra) include their sensitivity to stress, their sensitivity to certain anaesthetic regimes and their unsuitability for standard collar mounted radio-transmitters. We examined the practicability of various field techniques for overcoming these issues in east and south east Ireland from April 2005 to July 2006. Thirty-four highly-stressed otters were restrained with ketamine and midazolam within minutes of capture, to fit externally-mounted transmitters or to transfer them to transport boxes. Eleven otters were fitted with harness mounted radio-transmitters, 2 were fitted with glued-on radio-transmitters and 15 were surgically implanted with intra-abdominal radio-transmitters in the field. The intra-abdominal transmitters were implanted under isoflurane anaesthesia within an hour of initial sedation. We experienced no complications with this anaesthetic regime. The abdominal cavity was accessed by a lateral approach. All surgeries were successful and we recorded no serious post-operative complications. The implantation procedure lasted less than 3 hours from capture to release such that almost all animals stayed within their territories, and pups were not abandoned. However, following their release, animals were sensitive to directed disturbance and could easily be forced to disperse.