Field techniques for handling, anaesthetising and fitting radio-transmitters to Eurasian otters (Lutra lutra)

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.