Sea otters (Enhydra lutris) play an important role in maintaining the health of the kelp ecosystem in temperate coastal regions of the North Pacific Ocean. Sea otter predation plays a role in shaping the diversity, abundance and dispersal of invertebrates, including those grazers which control the establishment of kelp. Throughout this intricate organization, sea otters can serve as indicators of the overall health of the coastal marine ecosystem.
Current estimates put the North Pacific sea otter population at less than 100,000. As a consequence of the heavy demand for sea otter pelts in the 19th and early 20th centuries, the Canadian population of sea otters was extirpated by 1929. Translocation efforts were carried out between 1969 to 1972. A 1998 survey estimated the British Columbia (BC) sea otter population at 2,000 along the west coast of Vancouver Island and 500 on the central coast of BC south of Bella Bella. The sea otter population in Canada is currently listed as 'threatened' by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), and is therefore protected under the terms of the Species at Risk Act.
Because of their threatened status, baseline information is needed on the health of individuals and the threats facing the population. As part of a broader study to characterize infectious diseases, contaminants, and genetics, we conducted an evaluation of serum chemistry and hematology in free-ranging sea otters that were live-captured using entanglement nets near Nootka Island, BC, in September 2004. The sea otters were captured under the terms of scientific and animal care permits issued by the Canadian Department of Fisheries and Oceans.
The otters were sedated with an intramuscular injection of fentanyl (0.22 mg/kg) and diazepam (0.07 mg/kg). Whole blood was collected from the jugular vein using a Vacutainer system. Following blood collection, the whole blood (EDTA) and serum (no additive) were shipped within 24-48 hours to the Central Laboratory for Veterinarians (Langley, BC) for complete blood counts and chemistry screen. Hematological data generally fell within reference ranges from other studies. The wide ranges of some of the data may reflect individual variation, pathological processes not detected during physical examination, or stress-associated influences resulting from capture operations. However, we did not discern any stress-associated anomalies such as neutrophilia, monocytosis or lymphocytosis, suggesting that stress may have been minimal. Elevated levels of blood urea nitrogen may reflect the high protein diet or high metabolic rates of sea otters. The high levels of creatinine phosphokinase detected may be the result of muscle damage from the capture and the time spent in the net.
This study provides a baseline for free-ranging sea otters, which should prove useful as a reference for long-term monitoring of the health of the BC sea otter population, as a tool for rehabilitation and treatment in captive facilities, and as a tool in the event of an oil spill or other major incident. This information will therefore assist those scientists, conservationists and decision-makers involved in the sea otter recovery team in Canada.