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Grey nurse sharks, also known as sand tiger sharks, look toothy and formidable, but a new study finds they are actually curious about certain divers, whom they do not attack or bother.
The findings, published in the journal Tourism Management, indicate that scuba diving tourism can exist in the eastern Australia habitat of critically endangered grey nurse sharks, so long as divers behave a particular way and strictly follow guidelines.
If people comply, lead author Kirby Smith told Discovery News that the sharks will "often passively approach divers before slowly moving past them and remaining within close range." She added that sometimes "more than 30" large sharks at a time will come right up to particular divers and harmlessly check them out.
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The experience is quite memorable, given the look of these sharks.
"Grey nurse sharks grow to about 3.2 meters (10.5 feet) in total length, have a stocky appearance and have three rows of exposed teeth on the upper and lower jaws that protrude from the mouth," said Smith, who is a researcher in the School of Engineering and Science at Victoria University.
She explained that the sharks are so scary looking that they were "heavily targeted by spear-fishers in an attempt to exterminate the species from the east Australian coast." Now, the population of the sharks there is estimated only to be between 1146 to 1662 individuals.
Due to commercial and recreational fishing, global populations of this shark have also experienced sharp population declines.
For the study, Smith and her colleagues assessed diver and shark interactions at four off shore sites along the Australian east coast from March 2011 to February 2012. Smith, an experienced diver herself, previously noted that the sharks would exhibit disturbing behavior, such as erratic swimming and jaw gaping, around particular divers.
She called for strict adherence to guidelines, which say that divers must not touch, feed, chase, harass, or interrupt the swimming patterns of the sharks. They must also not block the entrances to caves or gutters, not wear mechanical devices, or dive in groups totaling more than 10 divers (up to 12 are OK, provided the extra two are diving instructors or guides).
The scientists found that grey nurse sharks do not ignore compliant divers. They instead appear to display intense, non-threatening curiosity about them, and even hover, cruise and mill around such well-behaved divers.
Marine biologist and veterinary surgeon Eric Clua, based in French Polynesia, also conducts research on shark behavior and management of shark tourism.
He told Discovery News that he was surprised that tourist divers at the east Australian sites were so compliant with the guidelines.
"If you allow me to compare what's happening in eastern Australia and other shark diving sites around the world I would say that the kind of harmony described by Smith et al. is strongly linked to the profile of most of the divers (mainly their affinity to marine life and respect of it), and the profile of the grey nurse sharks that, in spite of an aggressive appearance, are very nice animals," Clua said.
He added, "I would not say the same about lemon sharks, bull sharks or even grey reef sharks."
He, Smith and the other researchers hope that well-managed shark tourism programs will encourage people to value sharks more.
As Smith said, "Research has shown that a live shark is worth much more than a dead shark, and studies such as ours show that people and sharks can have a beneficial coexistence."