Keeping tabs on where whale sharks go

Using satellites to track whale shark migration around the world.
11 July 2017

Interview with 

Brad Norman and Sam Reynolds, Ecocean


We’re heading back to the Ningaloo Reef where not only did Chris manage to go swimming with whale sharks, he also caught up with Ecocean marine biologist Sam Reynolds. Her job it is to track these magnificent creatures, because we don’t actually know where they go across the world’s oceans. First, here’s Brad Norman again...

Brad - We’re trying to find out their migration using some satellite tracking to see where these animals are traveling when we don’t get the chance to see them or take photographs of them.

Chris - Doesn’t that mean you have to catch a 12-metre long fish in order to tag it?

Brad - Not quite. We have to do this in situ. I have to actually swim alongside a very large shark and put a tag on his dorsal fin while I'm swimming along.

Chris - How does the shark take to that?

Brad - Well, we’ve been very, very careful over the years. We’re making sure that the work that we do is minimal impact issue with the tagging. So we want to cause as less hassle to the animals as we can. So we’ve got a very simple, but a very low impact tag that we actually tag on the dorsal fin, and that seems to stay on on the shark. It doesn’t even react which is fantastic.

Chris - So rather than actually having to make an injury by penetrating the cartilage of the fin to hold the tag in, you're not doing that which is one way of doing it. You're actually having something that lightly attaches for long enough for you to get data.

Brad - Correct, yeah and the idea is using a spring clamp. We can just sort pressure onto the dorsal fin. Now, that’s not going to stay on forever which is fine because the last thing we want is these tags to remain on and fester, and cause damage, and so on to the animal. The idea is specific that these clamps and tags will stay only for a period of time, after which, they will fall away and leave no damage on the animal. We’ve got evidence to show that when we’ve resighted individuals that we’ve tagged the year before. Clamps, tags come off, no damage to the fins.

Chris - You said this is to monitor migration patterns, so you must therefore be using something like GPS or satellite monitoring or something. That uses radio signals and they don’t work underwater. How are you getting around that?

Brad - Well, that’s very interesting. What we found out was that the sunlight transmissions don’t go through water. So satellite tracking work well for a land-based animal or a dolphin or a whale, or a turtle or dugong, or something that comes up for air. Whale sharks are sharks. They don’t need to come to the surface. However, we used a different type of tag to understand more about the general behaviour of whale sharks called a daily diary. We were able to establish at certain times usually dawn and dusks, whale sharks while they're feeding at the surface, their actual dorsal fin is out of the water. and so, if we put a tag on that dorsal fin, it won't be pinging all day every day, but it will get enough transmissions to find out the position of that animal over a period of time.

Sam - Hi. My name is Samantha Reynolds. I'm a marine biologist and I work with Ecocean on whale sharks, and we’re here at Ningaloo Reef. It’s my job to download the transmissions that we get from the satellite tags. We do this from our website. The satellite company collects the data for us and we log in to the website, download the data, gives us a position, a time, and a date of when the whale sharks are at the surface. And then we take this data and we upload it to another website which then visualises the data. It’s a pubic website so anyone can go to the website and see the tracks of whale sharks that we’re getting.

Chris - Where do they go?

Sam - Good question. We’ve tracked a lot of them north from Ningaloo, northeast, northwest. We had one shark that travelled all the way to the southcoast of Java in Indonesia, and we also had one shark that travelled all the way down to near Rottnest Island of Perth. A few sharks visited Shark Bay. The pattern that we’re getting from the whale sharks is that they seem to stay in coastal waters. These are mostly juvenile males that we’re tagging. And so, we think that they're staying closer to the coast. We’ve also had the first fully tracked return migrations of whale sharks to Ningaloo Reef.

Chris - What does that mean?

Sam - We tagged the whale sharks here at Ningaloo Reef, we watched them move away from Ningaloo Reef. From my analysis, I said at least 300 kilometres away from where they were tagged and then we watched them come back again. The interesting thing is that it’s thought generally that whale sharks aggregated at Ningaloo Reef in the winter. But from the tracking that we’ve been doing, it looks like they're actually returning throughout the year. We had sharks returning in September or October, January. So, it looks like they could be using Ningaloo Reef all year round which is really interesting.

Chris - The ones that we were swimming with today were huge. They were maybe 8 metres long. It’s a size of a big bus bobbing around in the water with you. But what may surprise many people and it certainly surprised me was, that’s not a big animal. They get much bigger than that.

Sam - No, they can get a lot bigger than that. They can get up to 18 to 20 metres we think and at around 8 to 9 metres, they're starting to get mature. And so, we think that these coastal aggregations or collections of whale sharks if you like, the juveniles, and they're sort of building up their strength maybe, and then as they get bigger and mature, maybe they move further off shore, maybe to find a mate.

Chris - Why is it so important to study them because there are – use a horrible phrase – plenty more fish in the sea? Why are these ones important?

Sam - They're the biggest fish in the sea. They're the top of the food chain. We don’t really know what the effects would be of taking them out of that food chain, and do we really want the biggest fish in the sea to become extinct under our watch? I certainly don’t. So, I think it’s important that we study their threats and where they're going, and try and understand their movements so that we can protect them and areas that are important to them.


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