Pregnant grey nurse sharks (Carcharias taurus) are wandering away from no-take marine protected areas at night, putting the fierce-looking but mild-mannered species at risk of extinction. Not only that, but the critically endangered shark has only about 400 breeding individuals left in the wild, according to a 10-year study that tracked 34 grey nurse sharks migrating between the Great Barrier Reef and southern New South Wales (NSW).
Commonly known as the ‘grey nurse shark,’ ‘spotted ragged-tooth shark,’ or ‘sand tiger shark,’ this species can be found in various parts of the world, including eastern Australia where they inhabit coastal waters, including rocky reefs, coral reefs, and offshore islands. Known to congregate at a number of sites along the coast of NSW and southern Queensland at “aggregation sites,” they travel hundreds of kilometers between these sites in short periods of time, returning to the same location in consecutive years. One of the more distinct-looking sharks, they’re known for their protruding mouth and sharp, jagged teeth, which give them a fierce appearance despite no recorded shark bites in the oceanic continent and generally not considered a significant threat to humans unless provoked or cornered. However, this scary-looking appearance coupled with their large size has led to the eastern Australian population to drastically decline due to overfishing, habitat destruction, and the historical misconception that they are dangerous to humans.
Numerous conservation efforts are in place to protect their habitat, reduce fishing pressure, and raise awareness about the importance of their conservation. But famous shark activist Valerie Taylor has publicly stated this isn’t enough. And this collaborative research led by Dr. Ross Dwyer of the University of the Sunshine Coast and Dr. Carley Kilpatrick from the Queensland Parks and Wildlife Service (QPWS) shows things are more dire than was previously thought. The scientists have found the migratory sharks regularly visited no-take MPAs established along Australia’s east coast.
Flat Rock, Henderson Rock, and Cherubs Cave are frequently visited by migrating male and female sharks during winter through early summer. “In contrast, Wolf Rock was particularly important for pregnant female sharks which would stay at the site for up to 254 days during their gestation. However, sharks regularly left the relative safety of the MPAs, often in darkness,” Dr Dwyer said. “These excursions will likely increase the risk of them becoming bycatch – getting accidentally caught in commercial or recreational fisheries or in shark control equipment along beaches.”
“These night-time excursions suggest the existing no-take MPA at Wolf Rock needs to be larger to protect sharks in areas we now know they use, and help ensure the species’ long-term conservation,” explained Kilpatrick. “The tracking also revealed a longer than expected three-year migratory cycle linked to breeding. This slow reproductive rate, with females not breeding until they are at least nine years old and having a maximum of two pups at a time, highlights why the population has been so slow to recover.” However, both scientists are concerned that while Australia’s no-take MPAs do a great job protecting grey nurse sharks while they congregate in them, they are spending much more time outside of them than they thought — including areas adjacent to no-take MPAs like Wolf Rock.
Dwyer said the study used for the first time a novel combination of latest animal tracking technology and shark counts by citizen scientists: “The study was a massive collaborative effort, and we’d like to thank everyone who helped count and tag the sharks, and maintain over 300 moorings along the Australian east coast where these tagged grey nurse sharks were detected – from Heron Island in the Great Barrier Reef to Montague Island in south east New South Wales. This approach produced accurate, valuable data and can now be applied to other migratory coastal shark species to ensure marine area networks offer maximum protection benefits.”