Following great white sharks
Great white sharks are iconic animals, but they're also ones that we know very little about. And they're on the watch list of threatened species that conservationists internationally are trying to save, despite the misleading portrayal of the animals in some films. But, for conservation efforts to be successful, we need to learn as much as we can about where these animals go, how they hunt, and what sorts of environments they actively seek out or avoid. Now we're a step closer to doing that. With cameras that temporarily latch onto the dorsal fin, researchers have got their first glimpses of the Great White's underwater world. Chris Smith spoke to Oliver Jewell from Murdoch University....
Oliver - So what we've effectively done is put camera tags on white sharks in one of the first ever studies to do that, and it's part of a longer term study where we've used lots of different techniques to study these animals and each filling in a new part of the picture, but this one is really quite a big chunk of the puzzle which we just didn't see before.
Chris - One always gets a bit nervous when people talk about big chunks of things and great white sharks but where were you studying them?
Oliver - So this was all done in South Africa off Hans Bay which is in the Western Cape. Just offshore there's a really interesting island system and it's called Dyer Island and the seal colony is actually on Gyser Rock where there is 50 to 60,000 Cape Fur seals depending on the time of year and it attracts what was the largest population of great white shark anywhere in the world.
Chris - So how did you actually get cameras onto these things because these are big animals for a start aren’t they?
Oliver - Yes.
Chris - And they're not known for being particularly friendly necessarily, so how did you solve both of these problems?
Oliver - I worked for many years on a cage diving vessel and we kinda use the same technique. You put a bit of fish in the water and you use either a seal shaped decoy or a piece of bait and the shark swims up towards it. While the shark’s looking at this piece of bait or decoy, someone will lean over the side of the boat with a pole and a clamp and clamp these tags to the fin of the shark.
Chris - When you say “clamp” because one of the worries that marine biologists and the wider scientific community have is that we don't injure these animals when we tag them, so how do you satisfy the necessity to study but not harm?
Oliver- Well, with these clamps they're corrodible. So they'll fit onto the dorsal fin, but after a certain amount of time the tag pops off and comes to the surface so we can retrieve it and then the clamp falls apart and falls off the fin. So we don't want to leave any part on the animal beyond a week or so.
Chris - And as the animal's swimming so you've got video capture of where it's going and what it's seeing is that being stored on the camera device so that when it does resurface and you retrieve it that's when you get the data back?
Oliver - Yeah, exactly. We don't get anything if we don't get the tag back. So it's always a big risk when you put this expensive piece of equipment out in the ocean and then you have to hope that it films something good. It's also got a high-resolution motion sensor inside that's a bit like Fitbit and so every second there's 40 pieces of information going in on the heading of the animal in three-dimensions, the depth it’s swimming at, as well as the video. And then when it comes to the surface we've got either a satellite tag or a VHF tag on it so we can hopefully track it down, and if not we write our email address and hope that somebody emails us.
Chris - What was it like when you look at the footage and you are able to pursue these animals on their day-to-day business - any surprises? What did you see?
Oliver - Oh well I mean, for the most part the animals are just swimming. We've got to get good visibility too. Often it's really murky and the shark is just sitting there swimming along and you don't see anything exciting. But just every so often, something will catch shark's eye and it will start moving and we had one where the water was really clear and the shark was kicking up towards the surface and I was trying to see ‘What's it going for? It must be going for a seal or something’, and then it gradually slows and you look up and you see the surface, and you see above the surface there's a seagull flying and this shark just tracks it. For whatever reason this shark must have had a look at the seagull and decided I’m going to go and swim up and see what that is.
Chris - So in some respects it's not just telling us about where the animals go, it can also give us useful information about their behaviour and not just how they react to stimuli underwater either?
Oliver - Exactly that. I mean we can see different portions of time that these animals might be spending doing one behaviour versus another. We can see how much they move up and down the water column and how many times they beat their tail per minute. So we can see a lot more of these animal's day-to-day lives than we would be able to with a traditional tag that might give you a position every week or so.
Chris - And what are you going to do next?
Oliver - So what we're doing at the moment is building quite a large dataset where we're putting these tags or similar on white sharks in South Africa, in California, and possibly in other places as well, and then we really will be able to make a global comparison in their foraging patterns. And we’ll be able to look at things like how they change over time as they get larger and their prey preference will change for instance. We'll be able to track how they do that in terms of activity, in terms of their foraging aggregations in many places across the world.