NEW RESULTS ON A BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) COMMUNITY AT RANGIROA ISLAND (FRENCH POLYNESIA)

Abstract

INTRODUCTION By studying and comparing dolphin populations living in different habitats, we will be able to isolate the environmental factors shaping the range of behaviors this polymorphic species has developed. At Rangiroa Island (Tuamutu – French Polynesia), a population of bottlenose dolphins is described by the locals to be visiting the Tiputa pass almost every day, all year-round. A first study was conducted during four weeks from mid October to mid November 2001 in order to better understand the residency pattern, population size, habitat use, and social structure of this community. MATERIALS AND METHODS Study area The atoll of Rangiroa has two passes. Out-flowing and in-flowing currents strongly influence the sea state in passes by making the waves respectively appear and disappear for periods of nearly 6 hours.. One of the passes, the Tiputa pass, covers an area of roughly 0.2km 2 . Its depth ranges from 15 to 60 m. For the purpose of this study, the pass was divided into two zones (zone I and zone II) based on their characteristics. Zone I is from 25 to 60 m deep, coral covers the bottom, and the waves, if present, are stronger than in zone II. This second zone is less deep, and its bottom is sandy. A third zone, called "zone III", is the edge of the pass at the ocean side. Deeper than the two other zones, no current is observed. The waves, if present, are wind-induced and not a result of in and out-going currents. Shore-based surveys Day long surveys Five complete days of 11 hours and 40 minutes each were spent on the pass shore to record every 15 minutes dolphin absence/presence, their relative activity, the direction of the current, the force of the waves, the meteorological parameters and the absence/presence of boats. 4pm to 5pm surveys During 11 days, a one hour period from 4pm to 5pm was spent on the pass shore to record every 5 minutes dolphin absence/presence, their behavioral sequences, the direction of the current, the force of the waves, the meteorological parameters, and the absence/presence of boats.