Two female dusky sharks, Sylvie and Judy, have recently returned, after a two-year absence, to the area near the Orot Rabin power plant in Hadera. This is the first instance of returning sharks since the launch of a 2016, long-term study of Mediterranean predators, when Sylvie and Judy were tagged by a research team from the Morris Kahn Marine Research Station at the University of Haifa.
“Sylvie and Judy, female dusky sharks, 10.07 and 9.48 feet long respectively, survived for almost two years in the Mediterranean Sea, which is known to be very hostile to sharks, and returned to the Hadera area,” Said Dr. Aviad Sheinin, head of the Super Predators Department at the Maurice Kahn Marine Research Station, Department of Marine Biology, Charney School of Marine Sciences, University of Haifa.
“Their return can provide us with additional insights into the breeding cycle of the female sharks, their long-term survival, growth rate and assessment of the size of the female shark population in the eastern Mediterranean,” Dr. Sheinin explained.
In order to collect data on the presence of previously tagged sharks without having to catch them again, most captured sharks receive their own acoustic tag—a kind of finger-sized transmitter that transmits its unique shark’s code for about eight years. The data is received by various receivers deployed at several points along the Mediterranean Sea in Israel.
A recent examination of the signals revealed that the two ash-colored dusky sharks which had been tagged at the beginning of 2017 were back.
This is the first record of the return between monitoring periods.
“To date, we had observed that the tagged female sharks stay most of the winter in the hot water [near the power plant] and in the spring they leave and we haven’t seen them again,” said Dr. Sheinin. “We presume that the return of the sharks to Hadera’s hot water in the winter was connected to the sharks’ breeding cycle which lasts about two years. The first record of sharks returning after two years may explain this phenomenon.”
“This year, we will conduct ultrasound and blood tests to further investigate this unique phenomenon,” Dr. Sheinin said excitedly.