A few weeks ago I wrote about observing the mating behaviour of giant cuttlefish in July. Another marine creature that comes to our coast in winter to breed is the Port Jackson shark. The PJ, as it is commonly known, is by far the most common shark in our inshore waters and can frequently be found where there is rocky reef. Although it is named after Port Jackson, this is only because white settlers first saw them in that location. They are, in fact, widespread throughout southern Australia. The PJ is regarded as a primitive shark, by which is meant that it evolved at an earlier period than most other sharks and has changed little over millions of years.

The Port Jackson shark is a distinctive animal, usually a little over a metre in length, olive or grey in colour, with a striking harness-like pattern on its sides. Its scientific name is (Heterodontus portusjacksoni), the first part of which means ‘varied teeth’. It feeds mainly on molluscs – that is, sea snails of various kinds – and uses its pointed front teeth to dislodge its prey and then its flattened back teeth to grind down their shells. PJs spend much of the daylight hours resting on the ocean floor, mainly around rocky reefs, and often in groups of from two or three up to ten or more. Occasionally they will be seen swimming slowly and gracefully from one place to another. They are frequently seen by divers in our waters and can also regularly be seen by snorkelers. They are extremely docile animals and are quite harmless. They will allow divers and snorkelers to approach very closely. While you need have no fear of a PJ, if you see one when you are in the water, treat it with respect. Don’t harass it and you will both have a good day.

Port Jackson sharks gather in large groups in late winter/early spring to mate. They will be found in larger groups anywhere in our waters, but are particularly numerous in Jervis Bay. So numerous are they that they are an international attraction for divers. As part of the SCUBA diving survey work that Andrew Green and I do for a project called Reef Life Survey, we ventured up there in September to count sharks, other fish and marine life with Jervis Bay dive operator Sue Newson from Crest Diving. We found large numbers of PJs at a place called Dent Rock, which we reached by swimming from the beach near Vincentia. Unlike most sharks, PJs lay eggs, which are a leathery brown thing about 20cm long, with a corkscrew shaped projection running around its side, which the shark uses to secure the egg in a crevice in the rocky bottom. As well as sharks galore, we found eggs everywhere. We were so impressed that we decided we had to return at night, when we expected the sharks to be more active.

We were not disappointed. At Dent Rock we found sharks, sharks and more sharks, along with numerous other strange creatures. I came across a large conger eel, the first time I had seen one out in the open. A worm popularly known as the ‘green snot monster’ could be seen extending its tentacles from rock crevices. I found a mass of big ugly catfish writhing around in a hole. But it was the sharks we had come to see. They were everywhere. However, they were somewhat disoriented by our lights and it was quite disconcerting to have sharks bumping into you every few minutes and then darting away.

But the highlight by far was when I came across a couple of sharks mating, something that not all that many divers have witnessed. Shark sex is not a pretty sight, I hasten to add. The male, which is the smaller of the two, roughly bites on to the fin of the female and then, twisting his body around her, inserts one of his two ‘claspers’, or copulatory organs. I watched in some amazement as this was going on a metre away from me. My situation was not all that comfortable: the mating not surprisingly involves a fair bit of thrashing around on the part of the sharks. I was desperately trying to take some half-decent photos with my camera in one hand while holding a torch in the other and there was another male in the vicinity bumping into me as it was swimming around. After a few minutes the show was over and calm returned, though I felt privileged to have had the chance to be present as nature revealed some of its wonders.

If you are in the water in August or thereabouts, keep an eye open for our Port Jackson sharks: it will be worth braving the cold. As I said last time, make sure you are wearing an appropriately thick wetsuit, have a buddy to share the fun with and check the sea and weather conditions to make sure it is safe. But don’t go looking for sharks at night unless you are properly trained and/or supervised. And you may still share some of the mystery without going into the water at all if you are lucky enough to come across one of the Port Jackson shark’s eggs washed up on our beaches.