Recaptures
The overall recapture rate of sharks released from the nets is about 4%. It is interesting to note that the recapture rate of free-swimming raggedtooth sharks tagged by divers, where there is no capture stress, is higher (10.2%) than that of raggies tagged in the nets (4.7%). Recapture rates for other net-tagged species vary, e.g. 4.8% for the blacktip and 4.6% for the tiger shark.The overall recapture rate for injected sharks is 4.6% and 6.5% for the giant guitarfish. To date none of the other tagged rays has been recaptured. Here are some recapture highlights:
The three sharks which had the longest accurately recorded time at liberty were three raggedtooth sharks. One was tagged by a diver in 1990 and recaptured in 2002 (free for 12.8 years). Another one was tagged by a diver in 1991 and at the time of tagging already had an unreadable tag in it which was inserted in either 1988 or 1990. The shark was recaught at a fishing competition in 2002, tagged for the third time, and subsequently has been resighted by a diver in 2004. Thus the shark was at liberty for a minimum of 12 years. If taking the first tag from either 1988 or 1990 into account, the shark was at liberty for either approximately 14 or 16 years, respectively. The third one was tagged in 1997 and recaptured in 2008 (free for 11 years and 10 months). Another raggedtooth tagged in 1988 and recaptured in 1997 was free for 11 years and 4 months. This shark, however, also had an unreadable tag predating 1988 in it. The tag was possibly inserted in 1985 and thus the shark could have been free for over 14 years.
Raggies not only hold the record for the longest time at liberty, but also for the largest distance traveled. Two females tagged at Leven Point were recaptured (four and eight years later) in the Western Cape, traveling 1897 and 1710 km, respectively. Some tiger sharks also seem to like traveling. One tagged at Umtentweni was recaptured 401 days later in southern Madagascar. The minimum distance traveled was between 1530-1751 km. Another tiger shark traveled from Mzamba to the Mozambique Channel in 122 days. The minimum distance covered was between 1006-1200 km.
Other interesting recaptures include two "world-firsts". A great white and mako shark, both injected with oxytetracycline, were recaptured, creating much excitement amongst scientists. The white shark was tagged at a fishing competition and upon recapture 2.5 years later had grown 69 cm and gained 104 kg. The mako shark was one of the only seven injected animals to date and was recaptured one year later with no evident growth. Both recaptures were used for ageing work. The KZNSB is continuing with this project and it is hoped that the future will see further valuable recaptures of "tetracyclined-sharks".
Batoid recaptures are thus far restricted to giant guitarfishes, which do not seem to travel much. Two animals, both tagged at Amanzimtoti were both recaptured exactly three years later at the same location. Another animal, tagged 1991 in Ramsgate was caught four years later in Mzamba and then again 1997 in Port Grosvenor. It was at liberty for 5.3 years, traveling 72 km. The maximum distance traveled by a giant guitarfish was 320 km. The animal was tagged in Westbrook in 1988 and recaptured 3.5 months later near Shark Point in the Transkei.