The Cape Byron Leopard Shark Project with Dr. David Robinson

Dr. David P. Robinson, now the co-owner of Sundive Dive Centre in Byron Bay on the eastern coast of Australia, has been a friend of mine for years. David studied the whale sharks of the Arabian region for his PhD, but I wanted to talk to him about his new project, focused on leopard sharks, because they're wonderful.

In David’s words

The Cape Byron Leopard Shark Project

We moved to Byron Bay Australia from the Middle East in 2018. I love diving, and I wanted to help the marine environment as well, so we bought ourselves a dive center: Sundive. That's given us the chance to introduce lots of people to ocean life, and to start some new scientific projects as well.

I'd lived in Dubai since 2006, where I was working as the Assistant Curator for the Burj Al Arab aquarium. We had a lot of sharks within the exhibit there, including leopard sharks, so I was very familiar with the species.

I knew there was an aggregation of leopard sharks here at Julian Rocks, the main dive site off Byron Bay, but I wasn't really prepared for just how many sharks there are, and how special this place is. It was a no-brainer, really, to start a project looking at their ecology in the region.

I contacted the Cape Byron Marine Park. They thought it was a great idea and came on board, along with MMF of course. Together, we've formed the Cape Byron Leopard Shark Project to investigate all aspects of the species' life in this area. 

Leopard shark meetups

We've already identified that leopard shark behavior here in Byron is quite unique! Most of my prior diving experience was in the Middle East and, over there, seeing a leopard shark there was a pretty amazing event – you'd always be super stoked. In that region, we'd only see individual leopard sharks, and they'd usually be resting on the bottom. 

Here at Julian Rocks, you can have upwards of 50 leopard sharks swimming around you on a dive. We don't even have to move, as the sharks are swimming all around us. It's a very special site; I don't know of anywhere elsewhere in the world that's quite like this.

Julian Rocks is like an oceanic pinnacle, but located close to shore. We can access it easily, it's only a 2.5 km boat trip, but Cape Byron is the most easterly point of the Australian continent. Out past the Rocks, you're getting into deep water. Maybe that's why they aggregate here; that's what we're trying to find out!

Color-changing sharks

Leopard sharks change color as they grow up. We used to breed them in the aquarium and, when they're first born, they have vivid alternating dark and light stripes, which is where their other common name of 'zebra shark' comes from.

Our friend Dr. Christine Dudgeon, who is amazing, worked out that the young leopard sharks are actually mimicking sea snakes (and sea kraits). The sharks' relatively long tails give them a very sinuous movement when they're swimming, emphasizing their snakiness. They even have distinctive eyespots on each of their pectoral fins, so a potential predator looking down will see something big and venomous staring back at them, and presumably thinks "I'm going to leave that thing alone".

Monitoring leopard sharks

The 'leopard' spots in older sharks form from these 'zebra' stripes. The distinct stripes gradually change within a year or two to leave the spots behind, then this adult spot pattern seems to stay fixed for the rest of their life. That allows us to identify and monitor individual sharks over time. 

We had a fantastic 2020–2021 leopard shark season in Byron, carrying out dedicated surveys every week when the weather allowed. We identified 306 individual sharks that visited between December and May, with the total number of identified sharks from Julian Rocks now up to 387.

We've got a team of regular research divers here at Julian Rocks, but we've also got great support from the broader community along this coast. Anyone with a camera can submit images to the global database photo-identification database for leopard sharks, www.leopardshark.wildbook.org. We need the left side of the shark for ID: the area behind the gills and along the body. I just received photos from Wolf Rock, which is about six hours drive north of here, and even one from Tonga the other day, which was very cool.

Chris Dudgeon identified hundreds of leopard sharks during the 2000s at North Stradbroke Island, off Brisbane. She's uploading those onto the Wildbook website now. We've uploaded about 100 of her sharks so far, but we haven't had any matches with the recently identified Byron sharks. I was hoping for more excitement there, but it does indicate a large population size which is great.

We did get one match this year though. Chris had done some shark tagging at North Stradbroke back in 2005, and I noticed that one of the Byron sharks had an old tag insertion mark below its dorsal fin. That shark was already a mature male when Chris tagged it 16 years ago. We'd been estimating about a 25-yr lifespan for leopard sharks; I think we might be greatly underestimating their true longevity.

Isn't it romantic?

About 74% of our identified sharks at Julian Rocks have been adult females, with smaller numbers of mature males and sub-adults. Their behavior here is unusual. Most of them are swimming around during the day, constantly expending energy, whereas elsewhere, even at North Stradbroke Island, they're normally resting on the bottom through the day. 

I'm assuming they’re displaying some form of pre-mating behavior. We do see the males following females – and I have seen a photo of a male with engorged claspers – but we haven't observed any actual mating attempts. I'm kind of stumped on that one. Maybe it's occurring at night, and that's why we're not seeing it. We've got some ideas about deploying sensitive night-vision cameras over the upcoming summer to find out what's actually going on. Perhaps mating will happen at night, under the full moon. Very romantic.

Mystery of the baby leopard sharks

We don't see many juveniles in the wild, anywhere in the world. I've seen leopard shark eggs in the Musandam in Oman at about 30 meters' depth, near the limits of recreational diving. I think the sharks must be heading out to deeper waters to drop off their eggs. Recreational diving in eastern Australia is so well-established and widespread that, if the pups were within recreational diving limits, you'd have to expect that people would be seeing them.

"They're basically swimming tanks"

Leopard sharks don't have big teeth, they're more for grasping and crushing. They'll feed on things like octopus, fish, crabs, and lobster for instance. They can pretty much decimate these crunchy crustaceans.

I've never seen leopard sharks hunting in the daytime; they're mainly nocturnal predators. I suspect that smell is their most important sense for hunting. I've done some post-mortems on leopard sharks in the aquarium and the olfactory region of their brain is huge. They'll smell something tucked away within the reef, and they'll dig right into the rocks to get it. Their skin is extremely, excessively thick to protect them. They're basically swimming tanks.

Protecting Leopard Sharks

We think leopard sharks are doing okay on the east coast of Australia, but they're very much endangered in other parts of the world. They're such an easy target; they're harmless, coastal, and spend a lot of time sitting still on the bottom. They're one of the first sharks to disappear when fishing starts. 

I just saw a photo from the Andaman Islands, just north of the Maldives. About 50 sharks had been caught at once. They probably stumbled across an aggregation site, like Julian Rocks, and fished them out in a day. Boom, done. The sharks can't recover from that. We need to identify and protect these critical sites in advance.

That's part of what is so nice about working here in Byron Bay, as Julian Rocks is already a marine protected area. That said, they're only here from around December to May each year. We don't really know where they go after that. We'll try some acoustic tagging later this year and, of course, when divers submit photos it's extremely helpful for tracking the sharks. 

Thanks David!

*Largely to avoid confusion with an unrelated shark, also called a leopard shark, that lives in California. I'm just leaning into the confusion here... sorry.