Update: Scroll down for the latest on this story.
South Africa's Two Oceans Aquarium has successfully released two ragged-tooth sharks back into the wild – including one who's been an aquarium resident for 11 years!
The raggies were released in preparation for a maintenance closure at the aquarium, during which a larger predator exhibit will be built. Once secured, the animals were carted to the release site in a 6,000-litre holding tank on the back of a transport truck. The older of the two, a 240-kilogram (530lb) female known as "MJ", who has been with Two Oceans since 2005, was relocated first.
"Moving an animal that needs to be in water to breathe is, of course, not easy," says staff member Renée Leeuwner. "But we have been doing these releases for 12 years."
Unlike dolphins and other cetaceans, which are known to struggle with re-release, ragged-tooth sharks like MJ are hardy and seem to handle the move from captivity quite well.
The aquarium tagged and released its first raggie back in 2004, in conjunction with conservation groups Save our Seas and the AfriOceans Conservation Alliance (AOCA). That female, known as "Maxine", had spent more than eight years at the facility. Her release marked the beginning of M-Sea, a programme focused on raising awareness about ragged-tooth sharks and educating the public on the importance of the ocean's top predators. Since then, Two Oceans has been periodically releasing its captive sharks.
Maxine's tracker was programmed to pop off six months after her release, but in just that time, she travelled nearly 600km! The information from her tag, and those of the raggies released since, has given us insight into the sharks’ preferred migration routes, as well as clues about habitat use, including preferred water temperature and depth.
"Safety for the humans and the animals involved in the releases is always top of mind," says Leeuwner. "And, fortunately, we have developed systems and procedures that work very well."
Timing is also crucial, Leeuwner adds. The release site itself was carefully selected based on where wild populations of ragged-tooth sharks and their prey – typically small fish and crustaceans – are found in large numbers at this time of year.
Both "MJ" and her much smaller cohort "May" continued to hunt in their exhibit throughout their time at the aquarium, in addition to being fed. This is a good sign that their instincts are still sharp – but in case of complications, the animals were initially kept in a holding area before being released to the greater Atlantic.
"We do not foresee any problems with the sharks adjusting back to life in the wild or with their feeding behaviour," assures Leeuwner. "When we have tagged aquarium sharks in the past (with satellite tags), we have also tagged wild sharks at the same time. The data received back from the tags on the aquarium sharks showed that these animals behaved the same as the wild sharks."
Both May and MJ have been fitted with unique acoustic transmitters, which will alert shark scientists of their whereabouts as they cruise local waters for the next decade. If one of the sharks happens to swim past any of the listening stations along the coast of southern Africa, the tag's number will be recorded.
"Scientists are using every opportunity available to learn more about these incredible animals that have been roaming the earth’s oceans for more than 400 million years," adds the team. "Releasing sharks that have been housed at the Two Oceans Aquarium affords us a great opportunity to study ragged-tooth sharks in general and their migration patterns."
Two more female sharks will be released in the coming weeks. We'll be keeping you updated, so watch this space!
Update: Since the April release, two more ragged-tooth sharks have left their tank at Two Oceans Aquarium. Unfortunately, a minor injury meant that one of the animals could not complete her journey to the ocean, but will be released at a later date after some recovery time. The other ragged-tooth shark made it safely out to sea, and will now be tracked by scientists as she cruises local waters. We were lucky enough to film the first leg of the sharks' relocation:
__
Top header image: Saspotato, Flickr
Sharks
Sharks
Natural World
