Yesterday was windy but the ocean had almost no swell so the waves were relatively small and blown out.  Surfing wasn’t a great option so I grabbed my wetsuit and snorkel mask and went for a snorkel in Cabbage Tree Bay.  The sky was cheerful, mostly clear and sunny with the occasional puffy white cloud drifting by.  As I waded into the ocean from the beach I could feel the cool water gradually seep into my wetsuit.   The wind and choppiness further out churned up some of the algae and detritus but the visibility was still quite good. 

The giant clouds of jellyfish have all gone now as well as the big schools of juvenile fish but I was able to get some great video of Port Jackson Sharks.  Check out the short film below!

Port Jackson Sharks are endemic to Australia and inhabit the waters on the southern half of the continent, from New South Wales down around the southern coastline and halfway up Western Australia.   

Fact 1: Teeth and Diet
Unlike the vision of a shark you may be picturing in your head, with a giant mouthful of deadly sharp teeth, Port Jackson sharks’ dentition is quite different.  They have tiny sharp teeth in the front, perfect for capturing prey, and flat molars at the back, which are ideal for crushing the shells of their favorite meals – molluscs and echinoderms, including starfish, sea urchins, and sea cucumbers.  

Notice the two fins on the back of the shark.  These are the dorsal fins.  Can you see what looks like a white speck or point on the leading edge of these fins?  Those are their spines which are rumored to be poisonous.

Fact 2: Poisonous Spines
Although Port Jackson Sharks are generally considered harmless to humans, they do have spines on the front side of their dorsal fins which are rumored to be poisonous.  These spines are particularly sharp when the sharks are young and are thought to help protect them from predators until they are better able to fend for themselves.  

Fact 3: Very Unique Respiration
One of the most fascinating aspects of these sharks is their respiration technique. Port Jackson sharks can pump water into their enlarged first gill slit and expel it through the other four gill slits. This mechanism allows them to “breathe” without the need to constantly swim, enabling them to lie on the ocean floor for extended periods.  This is unusual for a shark since many sharks need to continue swimming in order to breathe.  

I’m pretty sure he sees me.  

Fact 4: Eyesight vs. Smell
These sharks are generally nocturnal so perhaps it should not be surprising but they are said to have poor eyesight.  That said, I have never been able to sneak up on them.  They always see me coming (or do they smell me?).  These captivating creatures primarily rely on their highly developed sense of smell to navigate the underwater world, making them excellent hunters in their own right.  

Notice that there is a fin on the underside of the shark’s body and just behind that fin you can see an oblong fleshy organ.  This is the male reproductive organ called the clasper.  

Fact 5: Reproduction and Sexual Dimorphism
Port Jackson sharks exhibit distinct sexual dimorphism.  Females, which are much larger, take 11 to 14 years to reach sexual maturity, while males, comparatively smaller, achieve this milestone in 8 to 10 years.  Reproductive organs called claspers can be found behind the bottom fin of male Port Jackson sharks (you can see this in the photo above).  I did not know this previously but female sharks tend to live in deeper waters and males in shallower areas.  So, the sharks we see in Cabbage Tree Bay are generally males.  The two groups only come together during the winter mating season.

Fact 6: Egg-Laying and Hatchlings
Port Jackson Sharks are oviparous and lay fascinating spiral-shaped eggs.  These eggs are placed in rocky crevices, beginning as soft structures that eventually harden. The outer shell of the eggs is composed of keratin, akin to human hair or nails. However, the odds are tough for these unborn sharks, as only 10% of the eggs survive to hatching, with many washing up on beaches or being eaten.   In fact, both male and female Port Jackson Sharks have been known to cannibalize the eggs.  If they are lucky, after a lengthy 10-12 months of incubation, the hatchlings emerge, measuring a mere 20-25 cm in size.   I really would like to find one of these eggs and watch it hatch!  

Fact 7: Migratory Patterns
Port Jackson sharks are migratory creatures, embarking on seasonal journeys. During the summer months, they feed in Bass Strait near Tasmania, while in winter, they migrate north to the warm waters of New South Wales for breeding, with Jervis Bay serving as a crucial destination. This impressive migration covers a staggering 600-800 kilometers between these regions.

Notice the black pattern that goes across the eyes and along the back and then splits at the dorsal fin?  This pattern is unique to the Port Jackson Shark.  

Fact 8: Bull Head Sharks (Heterodontiformes)
Port Jackson sharks are a type of bull head shark but there are others which look quite similar in many respects.  All bull head sharks have the pronounced brows or forehead ridges above the eyes and short, square snouts that make them look like something prehistoric (and for good reason).  The Port Jackson is distinguishable by the black harness-like pattern on it’s body that you can see in the photo above.   These sharks are in the order Heterodontiformes which includes only 9 living species but fossils of Heterodontiformes appear in the Early Jurassic Period, so these creatures have existed since the time of the dinosaurs!