Tracking sharks

A major threat to sharks the world over is the trade in their fins to be made into an expensive delicacy: sharks fins soup. Mahmood Shivji tells us about his work using molecular tools to track the shark fin trade - DNA extracted from a dismembered fin can tell us not only which species it came from but where in the ocean the shark lived. This is providing a powerful tool in monitoring and managing the trade and protecting threatened shark populations.

It's not just sharks that are targeted by the fin trade -  their relatives, the bizarre-looking sawfish, are in even worse trouble.

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Mahmood Shivji

Guy Harvey Research Institute

Save Our Seas, 
Sharks International Conference, 2010

Sawfish info from
Elasmoworld

Mahmood - We have some really good quantitative estimates now that tens of millions of sharks are being killed a year to supply the global shark fin trade. And in fact it could be as many as 73 million sharks a year. And that's a staggering number. No one is keeping track of which species and what numbers of each species are being killed worldwide to supply this trade. 

The best way currently to get a handle on this type of information is to actually monitor fin markets. 

Helen - How do you go from having a dismembered, dried shark fin to developing a genetic tool that's going to help us identify which species it came from?

Mahmood - In a way it's somewhat analogous, although I must add not identical, to DNA methods that are used in human crime cases.

The way we do this, over the past decade or so we've established an extensive reference database of DNA markers for 80 different shark species. We established this by collecting tissue samples with the help of colleagues around the world form wild sharks in the field as well as from sharks that have been landed in fishing ports.

Now we have this database of what are really species-specific DNA markers it's become really quite simple. It's just a matter of getting the fin or the meat from the market, analysing the DNA and then matching up the DNA from this body part to the reference database to identify which species that fin or that body part came from. 

Helen - What sort of species have you been working with and what sort of things have your studies been showing us?

Mahmood - The global fin trade consists of mostly around 50 shark species and you know some species are more common than others. As an example we did a market study with Shelley Clarke at Imperial College in the UK and showed that fins form blue sharks, short fin mako sharks, silky sharks and hammerhead sharks are the most common in the trade.

But surprisingly we also found fins form white sharks and both these species have small populations worldwide.

It turns out sharks are not the only elasmobranchs whose fins are valued in the fin trade. In fact there is another group called sawfishes. Sawfishes are a type of ray, they're related to sharks. Sawfishes are those rays that have a long nose or  rostrum, if you will, that has teeth on it. Sawfish populations have declined worldwide dramatically to a point where all currently six described species urgently need to be protected from fishing. And as a result all known sawfish species are now listed on CITES, with 5 actually listed on CITES appendix I. And what that means is that international trade in these species is now illegal for countries that are signatories to CITES, which is most countries. 

Helen - I take it there is still sawfish trade going on if your genetic studies are showing them up in trade? 

Mahmood - The most highly valued fins in the trade are actually from sawfishes. Some sawfishes have really large fins and as a result of overfishing, overfishing for the fin trade, as well as habitat destruction sawfishes have really taken the brunt of our overexploitation and their populations have declined tremendously.

Now, the problem is once you have a detached fin it becomes difficult to tell whether it's from a sawfish or whether it's from a legal to harvest shark. So what we've done is develop a quick genetics test that can distinguish fins form sawfishes from fins from other sharks and rays. It's sort of a generic test, it says that fin is from a sawfish and not from a shark or any other type of ray.

The beauty in this test is that it's really, really quick and therefore can be used practically. 

Helen - You've also been using genetics to pin down exactly what parts of the oceans they come from. Could you tell us a bit more about that?

Mahmood - What we did was that we actually looked at stock structure of scalloped hammerheads in the North and Southwest Atlantic. And we were able to find a clear genetic signature that would distinguish scalloped hammerheads from the Northwest Atlantic versus the Caribbean versus the Southwest Atlantic. We then went to the fins trade. We first identified fins are being from scalloped hammerheads. We then asked if some of those fins were coming from the Western Atlantic and we were able to match them up. 

And the reason that's important is because first of all it's sort of a proof of concept that you can tell not only what species the fin came from but what part of the world that fin came from. And it turns out in the Western Atlantic, scalloped hammerheads are severely overfished, in fact their populations have really crashed. And so the fact that we found fins from overfished populations in the fin trade tells you that there's a direct pathway, a direct channel from the Western Atlantic to Asian markets. And therefore more attention needs to be paid in the Western Atlantic to protect these stocks. 

Helen - Because your lab is also working on physically tracking sharks with various types of tags. How is that helping to build up a picture of where sharks move and how they use the oceans?

Mahmood - There's a critical need for migratory pathways of sharks and where sharks give birth and where they mate. One of the best ways to obtain that information is by tracking sharks. By putting on satellite tags, it will allow fine scale tracking of sharks over long periods of time. And what we're hoping to get at is to find first of all if there are specific patterns of migratory corridors, if you will, that individual species are moving along at certain times of the years. That's number one. 

Number two is to find out if females are ending up in areas where they give birth. Number three is to see whether both males and females are ending up in certain areas of the world at certain times where they're mating.

If we can find these places, define these corridors, and find these pupping and mating places, then those places can be protected in terms of fishing to make sure that these very sensitive demographic populations are not being fished. 

Brad Norman from Ecocean, a research group based in Australia, tells us about his pioneering work tracking whale sharks in Australia's Ningaloo Reef and beyond, taking inspiration from the stars.

Like a whale-shark version of fingerprints, they have unique patterns of spots that can be mapped using star-spotting algorithms. Brad describes the tools Ecocean have developed to manipulate photographs taken at any angle allowing them to rapidly and reliably pin down the identity of whale sharks .

Sadly, you can make a lot of soup from a single whale shark fin so it's no surprise there's a giant price tag on their giant fins. But Brad and his colleagues have shown that whale sharks can be worth far more kept alive in the oceans since they return many times to the same site where tourists happily pay for the experience of swimming alongside them.

Ecocean promote a sustainable model for whale shark ecotourism, offering a win-win situation for people and sharks. 

If you're lucky enough to spot a whale shark in the wild, you can get involved by sending your photos to the Ecocean project.

Find out more

Ecocean

Arzoumanian, Holmberg and Norman et al (2005).
An astronomical pattern-matching algorithm for computer-aided identification of whale sharks Rhincodon typus. Journal of Applied Ecology.

Whale shark (Rhincodon typus) info at the
Florida Museum of Natural History

Whale Shark Project,
The Shark Trust

Brad - Yeah for sure. I'm glad you're equally as excite about whale sharks as I am. Because I've been working on them since about 1995 and they're a beautiful creature and one that's threatened so we needed to learn more about them.

So the initial studies that I undertook were trying to identify individuals and work out how many whale sharks are at Ningaloo Reef in Western Australia and if the same ones come back and if in fact they're moving other places because so little is known about them.

They've got spots on their skin. Along with many other animals sometimes you can identify the animals through these natural markings. So I proceeded to take tens, hundreds, thousands of photographs and worked out by eye which individual sharks were which and whether we got matches.

That became a little be onerous, a little bit problematic, when you get thousands of photos.

I was very fortunate to link up with a couple of colleagues, Jason Holmberg who's a software engineer, and a good friend of his who's now a good friend of mine, Zaven Arzoumanian, who's a NASA astrophysicist. Zaven works on identifying start patterns in the night sky using a particular algorithm.

We bounced around ideas and came up with idea that we might be able to use an adaptation of this algorithm that the Hubble space telescope scientists used to identify stars in the night sky, we might be able to adapt that to basically identify individual sharks. It's sort of like a bit of fingerprint technology, really. 

And it's worked brilliantly. We've got many, many whale sharks in the library and many we can prove are coming back to Ningaloo Reef and other parts of the world using  this system.

Helen - Presumably you have to be able to get around problems like if you've taken the photograph from, say, different angles, maybe in different light conditions and so on.

Brad - The software, the way the system works, basically it deals with the angles between triangles of spots in an area behind the gills. Now that's great if you're side on the animal at 90 degrees and those triangles, those hundreds of triangles that the programme will draw of the pattern of spots, that will work perfectly.

But when you're not at 90 degrees to the side of the animal and you're taking a photo from behind or in front or below or above those angles get a bit screwed because of your angle to the shark. 

So, with actually come up with, well, it's not me, but a gentleman called Seth Ladiger, who's another programmer. He's come up with a system where we use 3D modelling. We take a photograph, put that photograph on a virtual 3D model of a whale shark. We then move the whale shark to be at 90 degrees and then we unwrap the photograph again. And what will happen is the angles will be what they would have been if you took the photo at 90 degrees. So it allows us to actually use those photographs that might not normally have been able ot be used. And it's working really well.

Helen - Do we know if those patterns change during the lifetime of an individual whale shark or do they really stay the same from when they're quite young to when they're much older?

Brad - Bearing in mind that when the whale sharks are born, they're very small. They're only half a metre in length. They can get up to, believed to be up to 20 metres. So, this is the beauty of the triangle system that we use. Although the animal will grow, the angles between the triangles that are drawn between all these spots, they will move equally as well so we don't see any change in the angles between the spot patterns over a period of time.

Helen - Wonderful, and what sort of things are you finding out from these tracking studies? What are we learning about the lives of whale sharks?

Brad - This system is letting us monitor the number of whale sharks that are coming to different locations. We started at Ningaloo Reef in Western Australia, but the Ecocean library is now expanded to receive photographs of whale sharks in 45 different countries now. So it's actually giving us a global monitoring programme for these species.

The long term study that we started at Ningaloo has shown us that may of the same whale sharks are coming back every year which is a great sign. Lots of new ones as well, which is really positive because it is regarded as vulnerable to extinction, their number shave been declining dramatically over the years.

What we've done in Australia is show that ecotourism can be an economic as well as an ecologically sustainable alternative to the once only value of killing a whale shark for fins.

But it's very, very important that it's not just an open slather and hundreds of licenses or boats potentially interfering with their natural activities. There's some basic things - you don't touch a whale shark, you don't get in their way, you don't have too may people around the animal, and you keep boats well clear.

Helen - A really important part of the Ecocean project, it seems, is drafting in the help of members of the public. Anyone lucky enough to spot a whale shark in the wild and catch it on camera can send the photos into the Ecocean photo library. Have you got any tips for taking useful photographs?

Brad - The simple thing to know is preferably be side on to the animal. The area we're mainly using for photo identification is the area behind the gills just above the pectoral fin.

As a scientist, myself and my colleagues can only be in one place, one day of the year. But we can have, and we are getting thousands of ecotourists that are becoming our research assistants. Their input is a really major part of our global monitoring system and we really appreciate it.