BIG BOLD AND BEAUTIFUL
Shark-loving Andrew Nieuwenhof tells us all about the iconic grey nurse sharks at his home in east Australia. All photographs kindly provided by Andrew's regular dive buddy Stephen Henley.
Diving among grey nurse sharks (Carcharias taurus) at my home dive location, Nguthungulli Julian Rocks, is an awesome wintertime experience. At peak season, you can sometimes see as many as 40 to 50 of these big, bold and beautiful seasonal visitors on the one dive, giving the impression that they are thriving.
But grey nurses along the east coast of Australia are still struggling to recover from near-extinction in the 1950s and 1960s, when they were heavily targeted by trophy-hunting spearfishers. Their population was estimated to be down to only 500 individuals when in 1984 the New South Wales government stepped in to protect them, declaring them critically endangered in what’s believed to be the first shark protection legislation in the world. There’s now estimated to be around 2000 of them on the east coast. Globally grey nurses are also listed as critically endangered under the IUCN’s Red List of Endangered Species. Since 1984, their recovery has been slow, due partly to their low reproduction rate in a mind-blowing process of natural selection in the womb. When a heavily pregnant grey nurse passes closely by, you can almost see what is going on inside: baby shark cannibalism. It’s called intra-uterine cannibalism or adelphophagy, whereby the largest and strongest embryo towards the end of the gestation period consumes its weaker womb-mate. Only one or two pups are born and then it takes at least another two years before the shark becomes pregnant again.
So far, the grey nurse is the only known shark species to practice this extreme form of reproduction. There’s a far more common method of intrauterine cannibalism in which developing embryos feed on a steady supply of tiny, unfertilized eggs. This is termed oophagy, “egg-eating” and is practised among lamnoid sharks, such as great whites, makos and salmon sharks, but is also being found in some other sharks.
In my twice-weekly dive at Nguthungulli, I can never get enough of being so close to these slow-moving toothy predators, some as large as 3.5 metres. Many of them seem to be just hanging there in a state of suspended animation, my dive buddies appearing almost, well, Lilliputian in their midst. They’re a formidable sight, teeth permanently exposed, their small eyes contrasting with their large size, their stout grey to grey-brown bodies speckled with the unique spot pattern that identifies each shark as an individual. Apart from their size, the thing you notice most are those prominent teeth. I have never actually seen one fall out, but like other sharks, grey nurses loose teeth continually, replacing them with new ones from a conveyor belt-like structure in their jaws. They can go through as many as 30,000 teeth in their lives.
You can kneel on a sandy patch and watch them coming up to you face-on until the last second when they veer away, or peer from behind a rock to see a parade of 10, 15 or more passing by. Sometimes you can be swimming along and, without warning, one or several of them will be next to you.
While they seem half asleep, they can explode into wakefulness, if startled. With a flick of their powerful tail, they will from a floating start burst out of the blocks at an astonishing speed and disappear into the distance. Most of the time they are in a mellow mood, earning the nickname labradors of the sea. Often these interactions will absorb you for the duration of the dive, making you feel as chilled as they are. One of the reasons for their adorable chillness is the unique additional way in which they control their buoyancy. While grey nurses have oily livers like all sharks to help keep them buoyant, they supplement this by swimming to the surface, sticking their head out of the water and gulping air, storing it in their stomachs as they descend. This is the reason we see so many of them hanging seemingly motionless in the water column.
Nguthungulli Julian Rocks Nature Reserve, in the species-rich Cape Byron Marine Park, is one of several known grey nurse aggregation sites stretching from Montague Island in southern New South Wales to Wolf Rock in central Queensland, a distance of more than 1600 kilometres. Grey nurses migrate over this distance, using Wolf Rock as a mating site before heading south to New South Wales to continue gestating and to give birth to their pups. My local dive site, marked by two rocks sticking up 20 metres out of the ocean, is only 2.7 kilometres from the beach and is easily accessed on one of Sundive Byron Bay’s two boats, which head out five days a week. Often you will see migrating humpback whales and Byron’s resident dolphins on the trip out and back. If you’re lucky you will score an underwater interaction with one or more whales. You will certainly hear them, often during the entire dive, their whalesong providing a fitting serenade to the grey nurse spectacle unfolding before us.
Since 2000, scientists with the help of thousands of photos provided by divers at Nguthungulli and other aggregation sites, have been monitoring the east coast population in a project called Spot a Shark. Using an AI program, scientists have been able to identify many individual sharks from those unique spots, helping to track shark movements, assess the overall health of the population, and monitor behaviour and changes at local aggregation sites over time. Hopefully this, amongst many other measures, will help to provide the long-term protection for this critically endangered species to allow us to dive amongst them for many more years to come.
NOTE: In Australia, they’re called grey nurses, while in the US they are known as the sand tiger shark and in South Africa, the spotted ragged tooth shark. The scientific name is Carcharias taurus.
