Immobilization of southern elephant seal bulls (Mirounga leonina) in polar regions

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Ramdohr, S. , Bornemann, H. , Plötz, J. and Bester, M. N. (2001): Immobilization of southern elephant seal bulls (Mirounga leonina) in polar regions , Verhandlungsbericht des 40. Internationalen Symposiums über die Erkrankungen der Zoo- und Wildtiere, 301-302, Rotterdam, The Netherlands .
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Extended AbstractStudies on wild pinnipeds such as blood and tissue sampling or attachment ofinstruments usually require immobilization. This is particularly true for adult malesouthern elephant seals whose body mass generally exceeds 2 tons, and hence,a suitable chemical restraint is required for any handling. Therefore, both appropriatedrugs and a remote delivery system as generally applied in wild animal research isrequired (CLINE et al., 1969; TRILLMICH and WIESNER, 1979; KOCK, 1987; BUSH,1992). Wild elephant seals are only accessable during their onshore-periods whilebreeding and moulting. At this time, they fast and hence undergo considerablemetabolic changes. The individuals' constitutions are then highly variable, and thereaction to external stimuli ranges from being calm to being aroused. Thereby, thedosage of drugs is hardly to assess, and the response to drugs is variable(HAMMOND and ELSNER, 1977). Estimation of body mass is also difficult sincemoulting males tend to aggregate tightly in large groups when ashore, occasionallylying over and over. The harsh field conditions in polar regions aggravate the workadditionally. Therefore, both a sturdy drug delivery system, and some considerationson the methods of application are recommended.In the present study, 27 animals were immobilized to obtain subcutaneous tissuesamples, and to attach satellite linked dive recorders to their pelage at the end oftheir annual moult. Prior to immobilization, doses were calculated roughly basedon the estimated body mass. Immo-bilization was performed in two steps. Firstly,Large Animal Immobilon® (LA Immobilon®) was injected remotely to achieveinitial sedation (x=0.0009 mg/kg etorphine; 0.0037 mg/kg acepromacine). As thesecond step, if breathing and reflexes occured regularly, ketamine wassubsequently injected by hand to maintain narcosis (x=81 min). Nine casesrequired the application of the etorphine-antidote Large Animal Revivon®(x=0.0052 mg/kg diprenor-phine) injected intraveneously (n=3), intramuscularly(n=5), or sublingually (n=1) to antagonize side effects such as prolonged apneaand/or decrease of reflexes.Results and DiscussionThe total dosages of ketamine required to maintain narcosis (x=1.7 mg/kg) werenegatively correlated with those of LA Immobilon® (p<0.01). The dosages ofLA Immobilon® were approximatelly 15-30 times lower than recommended forother large-sized mammal species including marine mammals (ALFORT et al.,1974; BORN and KNUTSEN, 1990; GRIFFITH et al., 1993), and the therapeuticrange was low. LA Immobilon® appears nevertheless to be useful as a first-stepimmobilization agent in adult male southern elephant seals owing to its smallvolume required for remote injection, and the possibility of high specificantagonization by Large Animal Revivon®. We nevertheless suggest thatLA Immobilon® should only be used as a kind of pre-medication, not usedrepeatedly in the same individual, and solely if high specific antidote(Large Animal Revivon®) is availlable. It has further to be realized thatLA Immobilon® is potentially dangerous for personnel, especially when usedin remote areas. Therefore, both the specific morphine-antidote for humans(Narcanti®), and trained field personnel should be aboard.

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