Field Anesthesia of Two Species of Pinnipeds (Arctocephalus galapagoensis and Zalophus wollebaeki) Found in the Galapagos Islands
American Association of Zoo Veterinarians Conference 2002

Alberto Parás1, MVZ; Dulce M. Brousset2, MVZ, PhD; Sandie Salazar3, PBSc; David Aurioles4, PhD

1Africam Safari, Puebla, México; 2Department of Wildlife Medicine, Ciudad Universitaria, National University of México, Mexico City, México; 3Department of Marine Investigation and Conservation of the Charles Darwin Research Station, Galapagos, Ecuador; 4Center of Marine Science, National Polytechnic Institute, Mexico City, México


In the Galapagos islands, two species of pinnipeds are found, the Galapagos fur seal (Arctocephalus galapagoensis),5 and the Galapagos sea lion (Zalophus wollebaeki)4. Because of the unique characteristics of their tropical habitat, both species have developed important features of endemism, such as corporal size reduction, physiological adaptations of thermoregulation, and specific behavioral characteristics.2,7,8,10 Both populations are relatively small, approximately 20,000–30,000 individuals9 and highly vulnerable to climatic changes, such as El Niño Southern Oscillation events8.

The Galapagos fur seal is found in the northeastern islands (Isabela, Fernandina, Santiago, Pinzon, Pinta, Marchena, and Wolf), in northeast Genovesa, and a small population exists in the central region (North Seymour, Baltra, and Santa Cruz).8 The Galapagos sea lion lives on almost all the islands, but the densest colonies are located in the southern and central regions of the archipelago (Española, Floreana, San Cristobal, Camano, South Plaza, Mosquera, and North Seymour).6

These pinnipeds, like other species of the archipelago, have a high risk of being affected by the introduction of exotic species (dogs, cats, and rats), and other problems, such as the most recent oil spill that occurred on San Cristobal Island in January 2001. Long-term vigilance and monitoring of health parameters in wildlife populations help to document changes in the prevalence of infectious agents and exposure to toxics. This data, together with general population dynamics and ecology, provides essential information that enables the interpretation of the state of health of both these pinniped populations and the ecosystem.

As part of a long-term study on the ecology, behavior, physiology, and epidemiology of the pinnipeds of Galapagos, the use of isoflurane as an anesthetic agent for handling pups and juveniles of both species to obtain quick morphometric measurements and biological samples was evaluated. Anesthesia with isoflurane has been reported in similar species to provide a quick induction, an ideal state of immobilization, a high margin of safety, and a complete and quick recovery.1,3

The field study was carried out on six different islands, in six rookeries of the Galapagos sea lion and in one rookery of the Galapagos fur seal. Each animal was restrained manually and isoflurane (Forane®, Abbott Laboratories Limited, Queenborough, Kent, UK) was administered at 5% in oxygen (1–2 L/minute) for induction using a portable anesthesia machine designed for humans. An endotracheal tube was placed in the majority of animals and the isoflurane concentration was adjusted according to stimuli response and the presence or absence of palpebral reflex and mandibular tone.

During anesthesia, the following physical signs were monitored: palpebral reflex, capillary refill time, mandibular tone, cardiac and respiratory frequency, oxygen saturation, and body temperature. A pulse oximeter with a rectal probe was used. Once the procedure was completed, the animals were maintained on oxygen until they recovered completely. Morphometric measurements, body weight, hair samples, blood (10–20 ml) from the jugular vein and select samples from pathologic lesions were obtained during the anesthesia period.

A total of 77 Galapagos sea lions (36 male and 41 female) were anesthetized for 4–26 minutes (mean 10.37, SD=2.45) with an induction time of 2–20 minutes (mean 6.26, SD=1.021). Animals ranged in weight from 5–23 kg (mean=12.42, SD=1.56). Six Galapagos fur seals (2 male and 4 female) were anesthetized for 11–18 minutes (mean=14.83, SD=2.48) with an induction time of 7–14 minutes (mean=10.5, SD=2.88). Animals ranged in weight from 16–23 kg (mean=18.33, SD=2.65). Mean pulse oximetry readings were 94% (range=90–98, SD=3.75), mean pulse rate was 116 per minute (range=91–146, SD=18.96), mean respiratory rate was 13 per minute (range=11–16, SD=2), and mean body temperature was 37.5°C (range=36.4–38.5, SD=0.9).

The physiologic parameters of the Galapagos sea lion obtained in this study, compared with those of the California sea lion (Zalophus californianus) obtained using a similar anesthetic protocol,3 were similar in pulse (mean=107 per minute, SD=4.5, range=82–158) and respiratory rates (mean=17 per minute, SD=1.3, range=9–38), but the oximetry readings were significantly better in Galapagos sea lions (mean=97.33%, SD=0.5, range=90–99) compared to California sea lions (mean reading=84.83%). Body temperatures of Galapagos sea lions never rose above 39°C (mean=37, SD=0.15, range=35.8–39), compared to body temperatures of 40°C and 41°C observed in California sea lions under similar environmental conditions.3

The Galapagos sea lions were much more tolerant to human presence than the California sea lions, and this behavioral characteristic may have benefitted the outcome of the anesthesia procedure. The small Galapagos fur seals, however, were more intolerant to human presence than the Galapagos sea lions and were more aggressive during physical restraint. The largest Galapagos fur seal handled (23 kg) never recovered from the anesthesia. The primary cause of death was attributed to shock related to capture, physical handling, and anesthetic procedure.

The use of isoflurane as an anesthetic agent for pups and juvenile Galapagos sea lions proved to be safe and practical for the handling of a large numbers of animals. Despite the few number of Galapagos fur seals anesthetized and the anesthetic death of one animal, we still consider the protocol useful, but for future projects the aggressive behavioral characteristic of this species should be taken into consideration.


The authors would like to acknowledge Peter Howorth and his team for the support of this project.

Literature Cited

1.  Heath, R., R. DeLong, V. Jameson, D. Bradley, and T. Spraker. 1997. Isoflurane anesthesia in free ranging sea lion pups. J Wild Dis. 33:206–209.

2.  Limberger, D., F. Trillmich, H. Biebach, and R. Stevenson. 1986. Temperature regulation and microhabitat choice by free-ranging Galapagos fur seal pups (Arctocephalus galapagoensis). Oecologi. 69:53–59.

3.  Parás, A., M.A. Benítez, D.M. Brousset, D. Aurioles, S. Luque, and C. Godínez. 1998. Anesthesia of California sea lions (Zalophus californianus) in 11 reproductive rookeries of the Gulf of California, Mexico. In: Proc Am Assoc Zoo Vet. 425–430.

4.  Sivertsen, E. 1953. A new species of sea lion, Zalophus wollebaeki. Det Kongelige Norske Videnskabers Selskabs Forhandlinger. 26:1–8.

5.  Thowsend, C.H. 1934. The fur seal of the Galapagos Islands, Arctocephalus galapagoensis (Heller). New York Zoological Society. Zoologica. 2:43–51.

6.  Trillmich, F. 1979. Noticias de Galápagos. Estación Científica Charles Darwin. 29:8–14.

7.  Trillmich, F. 1981. Mutual mother-pup recognition in Galapagos fur seal and sea lions: cues used and functional significance. Behav. 78:21–42.

8.  Trillmich, F. 1984. Natural history of the Galapagos fur seal (Arctocephalus galapagoensis, Heller). In: Perry R. (ed.). Key environments—Galapagos Pergamon Press. Oxford, 212–223.

9.  Trillmich F. 1987. Galapagos fur seal, Arctocephalus galapagoensis. In: Croxall, J.P. and R.L Gentry (Eds.). Status, Biology, and Ecology of Fur Seals. Proceedings of an international Symposium and Workshop. NOAA Technical Report Rep NMFS 51. Cambridge, Inglaterra. 23–27.

10.  Trillmich F., and E. Lechner. 1986. Milk of the Galapagos fur seal and sea lion, with a comparison of the milk of eared seals (Otariidae). J Zool Lond. 209:271–277.


Speaker Information
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Alberto Parás, MVZ
Africam Safari
Puebla, Mexico

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