Intra-abdominal Radio Transmitter Placement in North American River Otters (Lontra canadensis)
American Association of Zoo Veterinarians Conference 2001
Sonia M. Hernandez-Divers1, DVM; George V. Kollias1, DVM, PhD; Noha Abou-Madi1, DVM, MS; Barry K. Hartup2, MS, DVM, PhD
1Division of Wildlife Health, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA; 2International Crane Foundation, Baraboo, WI, USA


North American river otters (Lontra canadensis) from northern and eastern New York were captured as part of a translocation project during the months of September to November in 1998, 1999, and 2000. Radio transmitters were surgically implanted into the abdominal cavity of the otters to allow monitoring of the animals after relocation. The otters were maintained, assessed, and preconditioned for release at Cornell’s College of Veterinary Medicine as previously described.1 Otters which had not sustained severe trap-related injuries, were in good body condition and health, and weighed more than 4 kg were selected for radio transmitter implant surgery (n=24).

The otters were anesthetized with intramuscular ketamine (Ketaset, Fort Dodge Laboratories, Fort Dodge, IA; 15 mg/kg) and midazolam (Versed, Roche Laboratories, NJ; 0.4 mg/kg). After induction, the animals were intubated and maintained on isoflurane in oxygen throughout the surgical procedure. In contrast to previous reports of intra-abdominal implant surgeries in otters, our technique involved an approach through the paralumbar fossa.2-8 The otters were placed in right lateral recumbency and the hindlimbs were tied back. A 12×12 cm square was shaved immediately cranial to the cranial border of the hindlimb. The surgical incision was centered in the middle of this square. The skin, the subcutaneous layer, the cutaneous trunci muscle, and a thick layer of fat immediately deep to this muscle were sharply transected. The external abdominal oblique, the internal abdominal oblique, and the transverse abdominal oblique were dissected bluntly. The transverse fascia and parietal peritoneum were transected for entry into the abdominal cavity. The radio transmitter implants (Telonics Inc., Mesa, AZ) weighed approximately 28 g and were introduced into the abdominal cavity where they were allowed to free float. The surgical incisions were closed by suturing the abdominal muscle layer with 3-0 polydioxanone (Maxon, Davis, and Geck, Manati, PR) in a simple continuous pattern. The subcutaneous tissues were sutured with 3-0 polyglactin 910 (Vicryl, Ethicon, Johnson & Johnson Co., Somerville, NJ) in a simple continuous pattern. The skin was opposed with an intradermal pattern made with 3-0 polyglactin. No deaths occurred as a direct result of the surgical technique, but two complications were encountered. Approximately 10 ml of whole blood were lost as a result of hemorrhage during one procedure when a branch of the circumflex iliac vein was accidentally transected. The circumflex iliac artery runs on the lateral abdominal wall supplying the abdominal musculature and can be transected if the surgical incision is extended too far ventrally. The otter was treated with intravenous fluids for blood loss and recovered uneventfully.

Infection of the surgical incision occurred in another case, in which Pasteurella multocida, Staphylococcus aureus, Clostridium spp. and Fusobacterium spp. were cultured from the surgical incision. The otter was treated with metronidazole and enrofloxacin, the wound was cleaned daily with diluted chlorhexidine (Nolvasan, Fort Dodge Laboratories, Fort Dodge, IA), and the otter recovered uneventfully.

Following recovery from radio transmitter implant surgery, otters were released in the western part of New York State. Monitoring via radiotelemetry for 12–24 months post-release revealed that four otters died. Three died when struck by vehicles. The fourth otter carcass was never found. The radio transmitter was found, perhaps removed from the cadaver by a predator or scavenger. The remaining otters, including the two otters in which surgical complications occurred, became established in their new ranges. The intra-abdominal implants did not appear to affect their survival or reproductive potential.

The standard approach to the abdominal cavity of mammals is a ventral midline incision, which allows transection of the linea alba, a relatively avascular tissue plane. However, river otters rub their ventral abdomen as part of their grooming behavior, and this behavior can disrupt the surgical incision and promote surgical incision infection. The paralumbar surgical approach is recommended for the implantation of radio transmitters in North American river otters since it carries a lower incidence of surgical incision infection and dehiscence.

Literature Cited

1.  Kollias GK. Health assessment, medical management, and prerelease conditioning of translocated North American river otters. In: Fowler ME, Miller RE, eds. Zoo and Wild Animal Medicine: Current Therapy 4. Philadelphia, PA: WB Saunders Co; 1999:443–448.

2.  Hoover JP. Surgical implantations of radiotelemetry devices in American river otters. JAVMA. 1984;185:1317–1320.

3.  Melquist ME, Hornocker HG. Development and use of a telemetry technique for studying river otter. In: Proceedings from the second International Conference on Wildlife Biotelemetry; 1979; Laramie, WY. 104–114.

4.  Polechla PJ. A review of the techniques of radiotelemetry of the nearctic river otter. In: Proceedings from the tenth International Symposium on Biotelemetry; 1988; Fayetteville, AR. University of Arkansas Press. 14–22.

5.  Serfass TL, Peper RL, Whary MT, Brooks RP. River otter (Lontra canadensis) reintroduction in Pennsylvania: prerelease and clinical evaluation. J Zoo Wildl Med. 1993;24: 28-40.

6.  Spinola RM, Serfass TL, Brooks RP. Radiotelemetry study: river otter reintroduction at Letchworth State Park. Progress Report #1. New York Department of Environmental Conservation. 1995.

7.  Williams TD, Siniff DB. Surgical implantation of radiotelemetry devices in the sea otter. JAVMA. 1983;183:1290–1291.

8.  Woolf A, Curl L, Anderson E. Inanition following implantation of a radiotelemetry device in a river otter. JAVMA. 1984;185:1415–1416.


Speaker Information
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Sonia M. Hernandez-Divers, DVM
Division of Wildlife Health
Department of Clinical Sciences
College of Veterinary Medicine
Cornell University
Ithaca, NY, USA

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