Radio acoustic positioning as a tool for studying site-specific behavior of the white shark and other large marine species

We describe a method, radio-acoustic-positioning (RAP), for continuously mo nitoring the movements and behavior of large marine animals. An ultrasonic transmitter on the animal can be localized with high spatial accuracy (2 to 10 m) within an area of 1 km(2), based on when the same pulse arrives at t hree hydrophones on sonobuoys aligned in a triangular array. Radio transcei vers communicate with the base station, where the x and y coordinates of th e subject are calculated using hyperbolic equations. The base station plots the individual's position and displays information from the tag's sensors in real time on a computer monitor before saving the data on a disk. The ba se station must be situated either on land or on a vessel within the recept ion range of the three buoys. We used a RAP system to monitor the movements and behavior of white sharks (Carcharodon carcharias) near the elephant se al rookery at Afio Nuevo Island in central California. This type of system is an ideal tool to study the predatory behavior of the white shark because individuals patrol for seal prey within a zone <1300 m from shore. We desc ribe the operation of the system, including acoustic triangulation, range o f detection and positioning, data acquisition and analysis, and positional accuracy. We illustrate the implementation of the and its advantages and di sadvantages by method describing an ongoing study of white shark hunting-be havior. Sample data from this study are presented to illustrate specific po ints. We describe the movements of five sharks within the receiving range a nd their behavior relative to each other. The RAP system is compared to oth er complementary tracking methods. We conclude that this system has great p otential for monitoring the movements and behavior of large marine animals within a relatively small zone, where feeding or reproduction takes place.