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ULTRASONIC SHARK TAG MONITORING SYSTEM.
Technical rept., 1 May 68-30 Apr 69,
NEBRASKA UNIV LINCOLN DEPT OF ZOOLOGY
Pagination or Media Count:
The bull shark, Carcharhinus leucas, is a euryhaline fish that occurs, among other fresh water systems, in Lake Nicaragua and the Rio San Juan which drains it. The monitoring system described is used in a project designed to study the movements of the sharks between the Caribbean Sea and Lake Nicaragua. Ultrasonic transmitter tags, consisting of a pulsed oscillator, transducer, and mercury cell power supply, are fastened to the first dorsal fin of sharks. They transmit a pulsed 134 kHz signal for 14 to 1 mile and have a tag life of 12 weeks. The use of five repetition rates permits identification of five individual sharks or, in mass tagging programs, sharks from five separate groups. The ultrasonic tag monitor consists of two receivers, a recorder and batteries, all housed in a weatherproof metal case, and two hydrophones connected to the receivers by electric cable. The receiver-recorder unit is installed on the stream bank, the two hydrophones in the water nearby. The system provides 24 hour monitoring of selected sites. The passage of a tagged shark is recorded on tape, which identifies the repetition rate of the tag, the time of passage, and whether the shark was heading up or downstream. The monitors have functioned in the humidity and rain of the tropical Central American lowlands with a minimum of trouble. Author
APPROVED FOR PUBLIC RELEASE