Abstract
A total of 2,754 chemical immobilizations of free-ranging moose (Alces alces) were carried out in Scandinavia from 1984–2003 as part of ecological studies or for management purposes. Standard procedures involved darting from a helicopter in winter (November–April).
In Norway, etorphine (M99® 9.0 mg/ml, Novartis Animal Health, Litlington, UK) at 6.0–9.0 mg/animal was used for immobilization of 1,373 individual moose on 1,491 occasions (820 adult cows [≥1 year], 250 adult bulls, 244 female calves [<1 year], 177 male calves). Diprenorphine (M5050® 12 mg/ml, Novartis Animal Health, Litlington, UK) at 12–15 mg/9 mg etorphine was used for reversal. The overall mortality rate was 0.5%. Two cows (0.2%) and five calves (1.2%) died or were euthanatized during the capture process. One of the cows was hit high in the neck and died within 2 minutes of darting. This cow was pregnant and in good body condition. Necropsy showed possible intravascular drug injection and shock development. The other cow drowned during the induction phase when it tried to cross a deep river. Four of the calves died due to respiratory arrest shortly after darting. Necropsies showed poor body condition in all these animals. The fifth calf developed bilateral hind leg paresis and was euthanatized. Necropsy showed traumatic spinal lesions, caused by dart impact in the lumbar region, osteoporosis, cachexia, and verminous pneumonia. Follow-up radio telemetry was done for at least 1,222 of the animals (97.6%). No mortalities caused by the capture (residual drug effects, stress, exertional myopathy, or predation) were seen. The number of darts used per captured animal (including missed darts, multiple darts in some animals) varied from 1.2–1.5 in various projects. Average helicopter time per captured moose (including weighing of the animals) was 26 minutes for an experienced pilot and 35 minutes for a pilot with less experience, involving several projects (with the same experienced shooter) and different topography, vegetation, and moose density.
In Sweden, combinations of etorphine-acepromazine Large Animal Immobilon® (Novartis Animal Health, Litlington, UK) and xylazine (Rompun®, Bayer, Germany) were used for immobilization of 1,178 individual moose on 1,263 occasions (617 cows, 291 bulls, 173 female calves, 182 male calves). A drug mixture was made by adding 5 ml of Immobilon® (2.25 mg/ml of etorphine and mg/ml of acepromazine) to one vial of Rompun® dry powder (500 mg of xylazine) and the following doses were applied: 1.0–1.5 ml for adults and 0.5–0.7 ml for calves. Diprenorphine (Large Animal Revivon® 3 mg/ml, Novartis Animal Health, Litlington, UK) was used to reverse the effects of etorphine at a dose ratio at 12–15 mg/9 mg of etorphine. Initially, no reversal agent was used to counteract xylazine. However, since 1995 atipamezole (Antisedan® 5 mg/ml, Orion Pharma Animal Health, Turku, Finland) at 7.5 (adults) or 5 (calves) mg was used for antagonism of xylazine (935 captures). The overall mortality rate was 1.0%. Mortalities included seven cows (1.2%), one bull (0.3%), and four calves (0.6%). In five of these animals, all before 1995, atipamezole was not administered. One cow and one calf died due to exertional myopathy. One calf died due to respiratory arrest during immobilization. Five cows, one bull, and two calves were found dead close to the marking place days or weeks after immobilization. In addition, one cow was killed by a brown bear shortly after immobilization. For conservative reasons, these deaths are included as capture related. Follow-up radio telemetry within 2 weeks was done for all of animals. On average, 1.3 darts were used and 30 minutes of helicopter time (including ferry and weighing of animals) were spent per captured animal. No animals have died since 1997 and the mortality has been reduced drastically since 1995 when atipamezole was included as a reversal agent.
We conclude that etorphine or etorphine-acepromazine-xylazine are very safe and effective drugs for immobilization of free-ranging moose from helicopter in winter. A review of the literature showed that mortality rates routinely range from 6–19% during capture and translocation of free-ranging moose (drugs including carfentanil, carfentanil-xylazine, xylazine, succinylcholine) in North America.1,3 In Sweden, a mortality rate of 1.7% was found in 650 free-ranging moose immobilized with etorphine-acepromazine-xylazine from 1979–1984.4 By using immobilizing drugs with proven safety and by refining the capture methods, we believe that such mortalities can be significantly reduced.2 In our opinion, etorphine or etorphine-acepromazine-xylazine should be considered the drugs of choice for moose immobilization.
Literature Cited
1. Arnemo, J.M., T.J. Kreger, and T. Soveri. 2003. Chemical immobilization of free-ranging moose. Alces 39. In press.
2. Kreeger, T.J., J.M. Arnemo, and J.P. Raath. 2002. Handbook of Wildlife Chemical Immobilization. International Edition. Wildlife Pharmaceuticals Inc., Fort Collins, Colorado.
3. Roffe, T.J., K. Coffin, J. Berger. 2001. Survival and immobilizing moose with carfentanil and xylazine. Wildl Soc Bull. 29:1140–1146.
4. Sandegren, F., L. Petterson, P. Ahlqvist, and B.O. Röken. 1987. Immobilization of moose in Sweden. Swedish Wildl Res Suppl. 1:785–791.