Long-term real-time monitoring of free-ranging Bottlenose dolphins (Tursiops truncatus) in an aquarium using 5-hydrophone array system

Abstract

Long-term real-time monitoring of free-ranging Bottlenose dolphins (Tursiops truncatus) in the pool of the aquarium “Izu Mito Sea paradise”, i.e. in the enclosed observatory has been started from 22nd June 2008, and continuously conducted ever since then. The monitoring system consists of 1) a modified 5-hydrophone array system deployed in the pool, 2) a web camera placed overland for visual monitoring of the dolphins, and 3) the land base system to process and transmit the acoustic data from the hydrophones of the array and the video images from the web camera to the servers in real-time via internet. The echo-location characteristics of the Bottlenose dolphins in the pool and their behavioral changes in a long-term span have been initially observed and analyzed. Three echolocation phases (search, approach, terminal) have been observed. It is estimated that the dolphins are echo-locating the surrounding environment and targeting something else such as the array as a target. Solo burst-pulses emitted by one of two dolphins swimming side by side in the pool were also observed. For understanding the Bottlenose dolphins' behavioral changes during the long-term monitoring, the trend of the number of clicks recorded around the pool is applied for the analysis as an index of the dolphin's activities. The results show the trend and difference of the changes of the click number in each section of the pool depending on the time of day. Not only depending on the time, but also depending on natural phenomena, the dolphins' behavioral changes were observed. A definite trend of click number reduction is observed during the occurrence of an earthquake, even when they stayed underwater. Significant behavioral changes of the dolphins are also observed just after the earthquake. This indicates that the Bottlenose dolphins in the pool of the “Izu Mito Sea Paradise” did not actually “predict” the earthquake.