Abstract

Multi-year post-release monitoring of rehabilitated marine mammals is essential in establishing the success of rehabilitation. This is especially true when attempting to develop prognostic and release criteria for animals affected by specific conditions that may produce subtle clinical signs. One such condition includes the long term effects of domoic acid toxicity. Some California sea lions (Zalophus californianus) affected by domoic acid toxicity may exhibit neurologic signs such as intermittent seizures or behavioral changes. These animals may appear very normal most of the time and may fulfill release criteria including normal blood parameters, good weight gain, and apparent ability to avoid predators and forage on their own. However, it is not known how long these animals survive after rehabilitation because post-release monitoring using currently available techniques can be hampered by numerous factors. Telemetry in pinnipeds has typically depended upon the use of external tags glued to the fur (Lander et al. 2001). Post-release monitoring periods are thus limited by the intermolt interval of these species. More recently, subcutaneous VHF tags have been developed (Lander et al. 2005), but the often large distances which animals regularly travel limit the use of VHF tracking equipment. Satellite-linked telemetry transmitters used in long-range oceanic tracking cannot successfully uplink when implanted beneath the blubber layer of marine mammals. The purpose of this study was to evaluate the safety and efficacy of a novel satellite-linked Life History Transmitter that is implanted into the peritoneal cavity of California sea lions and transmits previously collected data after release from the body of the animal post-mortem. To our knowledge, this is the first report of the successful implantation of intra-abdominal instruments in pinnipeds.

The Life History Transmitter was developed by Texas A&M University's Laboratory for Applied Biotelemetry & Biotechnology in cooperation with Wildlife Computers Inc. The transmitter monitors body temperature and ambient pressure. Pressure changes are summed weekly to characterize dive effort. If a temperature outside of the physiological range is detected, it is assumed that the animal has died. Time and date of this event are stored, and pressure sampling ceased. After the sea lion has died, the implant will eventually become exposed over the course of decomposition, and is designed to float in the event that an animal dies in water. Once the transmitter has been exposed or reached the surface of the water, it will transmit all previously stored data to orbiting satellites. The Life History Transmitter is cylindrical in shape and measures approximately 122 by 42 mm with a weight of 110 g in air. The expected longevity is greater than 8 years.

To date, four (3M, 1F) California sea lions have been successfully implanted at The Marine Mammal Center and released. The animals weighed 67 to 196 kg (mean±SD = 128 ± 53 kg) at the time of implantation. Animals were anesthetized using 0.04 mg/kg medetomidine with 1.0 mg/kg of a 1:1 solution of tiletamine and zolazepam given by intramuscular (IM) injection. The two larger animals were injected with a carbon dioxide powered dart, while the two smaller animals were hand-injected. All animals were intubated and maintained with isoflurane in 100% oxygen for the duration of the procedure. The animals were given 1 mg/kg flunixin meglumine IM during the procedure for analgesia. At the end of the procedure, the medetomidine was reversed with 0.1 mg/kg atipamezole IM. Physiologic parameters including heart rate, respiratory rate, oxygen saturation of hemoglobin, core body temperature, and end-tidal carbon dioxide were monitored during the procedure.

An area of approximately 20 cm x 20 cm was shaved on the ventral mid-abdomen caudal to the umbilicus. Routine surgical preparation was used to sterilize the area. An approximately 8-10 cm skin incision was made along the ventral midline starting approximately 5 cm caudal to the umbilicus. Sharp-blunt dissection was used to expose the linea alba which was incised to expose the peritoneal cavity. The implants, which had been gas-sterilized using ethylene oxide were rinsed with sterile saline and inserted into the caudoventral abdominal cavity. Two animals received two identical transmitters each while the other two animals received only one implant. The incision was closed with a 5-layer closure using an absorbable polydioxanone monofilament suture. The linea alba and skin were closed with an interrupted cruciate pattern, while subcutaneous tissue, blubber, and the subcuticular layer were closed with a continuous pattern. Mean (±SD) total surgical time including skin preparation was 90 (± 9) minutes, while total anesthetic time up to the time the animal was standing was 121 (± 23) minutes.

All animals recovered uneventfully, were returned to their pen and pool enclosure after recovery, and were eating normally the morning following the procedure. The animals were monitored for 44 to 71 days post-operatively prior to release and all animals received a satellite-linked transmitter glued to the pelage prior to release. Monitoring of satellite data suggested that all animals exhibited normal movement and dive behavior up to the point of external tag failure. To date, no information has been received from the Life History Transmitters suggesting that none of the animals has died.

The successful implantation of the Life History Transmitter into these animals represents an exciting technological advancement for long-term monitoring of animals after rehabilitation. The use of the Life History Transmitter has a large potential in other species as well as free-ranging otariids. However, more animals should be implanted under relatively controlled situations to ensure the safety of the surgical procedure and the recovery of data from these instruments has yet to be evaluated.