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Home , Leopard seal, Zalophus

Ultrasonic vocalizations of seals (Hydrurga leptonyx) I ___

JEANETTE A. THOMAS, SHELDON R. , and WILLIAM E. EVANS

Hubbs Sea World Research Institute San Diego, California 92109 FRANK T. AWBREY :J San Diego State University San Diego, California 92182

The vocal repertoire of leopard seals (Hydrurga leptonyx) has been studied in the wild by Stirling and Siniff (1979) and by 0 10 20 30 40 Thomas and DeMaster (in press) using audio recording equip- ment. Using ultrasonic recording equipment, we conducted a series of studies on a captive and found it capable of producing sounds of up to 164 kilohertz. 4) i Ij) 1 LA The leopard seal was a 4-year-old female, originally beached in Australia, that has been in captivity at Hubbs Sea World Research Institute since 1979. Live anchovies and striped bass MILLISECONDS were introduced into her tank, and her vocal activity in re- sponse to these prey was recorded. Recordings were made using a Racal Store-4 recorder and Bruel and Kjaer 8103 and 8104 Ultrasonic sounds produced by a leopard seal. a-e: frequency- hydrophones (system frequency response: 0.03 to 150 kilohertz modulated chirps; f: frequency-modulated buzz; and 9: click train. for the 8104 and to 200 kilohertz for the 8103 ± 3.0 decibels). Since ultrasonic vocalizations tend to be directional, the two hydrophones were placed on opposite sides of the 5-meter- diameter tank. and advice on training the leopard seals. Sandra Barnett from The leopard seal responded to both of by produc- Hubbs Sea World Research Institute was the trainer of the ing a variety of low-amplitude sounds. Frequency-modulated leopard seal during these tests and provided invaluable support chirps, buzzes and frequency-modulated buzzes, and single in conducting this research. clicks, double clicks, and click trains were recorded (see figure). Peak frequencies were extremely variable, ranging from 4 to 164 kilohertz. The amount of frequency variability that can be at- tributed to directionality is unknown. The most common peak References frequencies were between 50 and 60 kilohertz. The highest frequency sounds were produced while the seal chased the Evans, W. E., and Haugen, R. 1963. An experimental study of the smaller target (anchovies). The FM chirps swept as much as 60 echolocation ability of the California sea californianus kilohertz in 4 milliseconds and were only 4 to 10 milliseconds in (Lesson). Bulletin of Southern California Academy of Science, 62, 165-175. duration. Kooyman, C. 1968. An analysis of some behavioral and physiological Vocalizations of such extremely high frequencies have never characteristics related to diving in the . Research Series, 11, 227-261. been reported in , perhaps because researchers rarely Poulter, T. C. 1963. Sonar signals of the . Science, 139, 753-755. have attempted recording at ultrasonic frequencies. These Poulter, T. C. 1967. Systems of echolocation. In R. G. Busnel (Ed.), sounds are similar to the ultrasonic echolocation sounds that sonar systems: Biology and bionics (Vol. 1). Jouy-in-Josas, France: bats and dolphins use to find prey or to orient in their environ- Laboratoire de Physiologie Acoustique. ment. Echolocation abilities in polar pinnipeds have been pro- Schusterman, R. J. 1966. Underwater click vocalization by a California posed by Poulter (1963, 1967) and Kooyman (1968) because it sea lion: Effects of visibility. The Psychological Record, 16, 129-136. would help them find food or navigate during the dark austral Scronce, B. L., and Ridgway, S. H. 1980. , Halichoerus: Echo- winter. All efforts to demonstrate this ability in pinnipeds ex- location not demonstrated. In R. C. Busnel and J. F. Fish (Eds.), perimentally have been unsuccessful (Evans and Haugen 1963; Animal sonar systems (NATO Advanced Study Institutes Series A, Life Schusterman 1966; Scronce and Ridgway 1980), but none of the sciences, Vol. 28). New York: Plenum Press. Stirling, I., and Siniff, D. 1979. Underwater vocalizations of leopard species studied are known to vocalize ultrasonically. We cannot seals (Hydrurga leptonyx) and crabeater seals (Lobodon carcinophagus) say yet if leopard seals produce these sounds routinely during near the South Shetland Islands, Antarctic. Canadian Journal of Zoolo- prey pursuit or if the sounds are merely a short-term response gy, 57, 1244-1248. to a novel situation. Thomas, J., and DeMaster, D. In press. An acoustic technique for We thank L. H. Cornell, D.V.M., and Bruce Stephens of Sea determining the haulout of leopard (Hydrurga leptonyx) and crabeater World, Inc., for their assistance and support in husbandry, care, (Lobodon carcinophagus) seals. Canadian Journal of Zoology.

186 ANTARCTIC JOURNAL