Contributions to Zoology, 67 (1) 71-77 (1997)H.H. de Iongh; B. Bierhuizen; B. van Orden: Observations on the behaviour of the Dugong (Dugong dugon Müller, 1776) from waters of the Lease Islands, eastern Indonesia

To refer to this article use this url: http://ctoz.nl/vol67/nr01/a03

Materials and methods

During June-July and September-October 1992, free-ranging animals were observed from the top of a cliff in Saparua Bay. This site (Fig. 2), which is situated approximately 6 m above chart datum (ELWS), provided an excellent view over the bay and a nearby monospecific seagrass bed of Halophila ovalis that covered approximately 2 ha at 7-10 m depth. During the study we measured turbidity with a standard Secchi disk; it ranged between 10-21 m. When a dugong was spotted, notes were made on the time periods the animal spent at the water surface (surface time), and on the time periods the animal spent submerged between two successive surfacing intervals (submerged time). The number of inhalations was recorded as the number of times its nostrils were seen above the water surface. Additional observations were made from small boats on 24 June, 5 July, 20 July, 14 September, and 23 October 1992 and during scuba diving surveys on 5 July, 18 July, 13 September, and 1 October 1992. Feeding behaviour, surfacing and diving behaviour, as well as responses to approach by boats or divers were registered. Three modes of surfacing were described: rolling, sinking forward and sinking back (Anderson & Birtles, 1978). The response of dugongs to approaches by one or more swimmers, or observers on a boat were described as: (a) no apparent response (continued routine activity), (b) curiosity, or (c) avoidance.

During each observation period, snorkling transects covering the seagrass bed (perpendicular to the coast and at 30 m intervals) were made to identify feeding track density in the meadow and a distinction was made between ungrazed and grazed patches.