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Basking sharks are awesome creatures. They are just magnificent. They grow 10 meters long. Some say bigger. They might weigh up to two tons. Some say up to five tons. They're the second largest fish in the world. They're also harmless plankton-feeding animals. And they are thought to be able to filter a cubic kilometer of water every hour and can feed on 30 kilos of zoo plankton a day to survive. They're fantastic creatures. And we're very lucky in Ireland, we have plenty of basking sharks and plenty of opportunities to study them.
They were also very important to coast communities going back hundreds of years, especially the around the Claddagh, Duff, Connemara region where subsistence farmers used to sail out on their hookers and open boats sometimes way off shore, sometimes to a place called the Sunfish Bank, which is about 30 miles west of Achill Island, to kill the basking sharks. This is an old woodcut from the 17, 1800s.
So they were very important, and they were important for the oil out of their liver. A third of the size of the basking shark is their liver, and it's full of oil. You get gallons of oil from their liver. And that oil was used especially for lighting, but also for dressing wounds and other things. In fact, the streetlights in 1742 of Galway, Dublin and Waterford were linked with sunfish oil. And "sunfish" is one of the words for basking sharks. So they were incredibly important animals. They've been around a long time, have been very important to coast communities.
Probably the best documented basking shark fishery in the world is that from Achill Island. This is Keem Bay up in Achill Island. And sharks used to come into the bay. And the fishermen would tie a net off the headland, string it out along the other net. And as the shark came round, it would hit the net, the net would collapse on it. It would often drown and suffocate. Or at times, they would row out in their small currachs and kill it with a lance through the back of the neck. And then they'd tow the sharks back to Purteen Harbor, boil them up, use the oil. They used to use the flesh as well for fertilizer and also would fin the sharks. This is probably the biggest threat to sharks worldwide -- it is the finning of sharks.
We're often all frightened of sharks thanks to "Jaws." Maybe five or six people get killed by sharks every year. There was someone recently, wasn't there? Just a couple weeks ago. We kill about 100 million sharks a year. So I don't know what the balance is, but I think sharks have got more right to be fearful of us than we have of them. It was a well-documented fishery, and as you can see here, it peaked in the 50s where they were killing 1,500 sharks a year. And it declined very fast -- a classic boom and bust fishery, which suggests that a stock has been depleted or there's low reproductive rates. And they killed about 12,000 sharks in this period, literally just by stringing a manila rope off the tip of Keem Bay at Achill Island.
Sharks were still killed up into the mid-80s, especially after places like Dunmore East in County Waterford. And about two and a half, 3,000 sharks were killed up till '85, many by Norwegian vessels. The black, you can't really see this, but these are Norwegian basking shark hunting vessels, and the black line in the crow's nest signifies this is a shark vessel rather than a whaling vessel.
The importance of basking sharks to the coast communities is recognized through the language. Now I don't pretend to have any Irish, but in Kerry they were often known as "Ainmhide na seolta," the monster with the sails. And another title would be "Liop an da lapa," the unwieldy beast with two fins. "Liabhan mor," suggesting a big animal. Or my favorite, "Liabhan chor greine," the great fish of the sun. And that's a lovely, evocative name. On Tory Island, which is a strange place anyway, they were known as muldoons, and no one seems to know why. Hope there's no one from Tory here; lovely place. But more commonly all around the island, they were known as the sunfish. And this represents their habit of basking on the surface when the sun is out.
There's great concern that basking sharks are depleted all throughout the world. Some people say it's not population decline. It might be a change in the distribution of plankton. And it's been suggested that basking sharks would make fantastic indicators of climate change, because they're basically continuous plankton recorders swimming around with their mouth open. They're now listed as vulnerable under the IUCN. There's also moves in Europe to try and stop catching them. There's now a ban on catching them and even landing them and even landing ones that are caught accidentally. They're not protected in Ireland. In fact, they have no legislative status in Ireland whatsoever, despite our importance for the species and also the historical context within which basking sharks reside.
We know very little about them. And most of what we do know is based on their habit of coming to the surface. And we try to guess what they're doing from their behavior on the surface. I only found out last year, at a conference on the Isle of Man, just how unusual it is to live somewhere where basking sharks regularly, frequently and predictably come to the surface to "bask." And it's a fantastic opportunity in science to see and experience basking sharks, and they are awesome creatures. And it gives us a fantastic opportunity to actually study them, to get access to them.
So what we've been doing a couple of years -- but last year was a big year -- is we started tagging sharks so we could try to get some idea of sight fidelity and movements and things like that. So we concentrated mainly in North Donegal and West Kerry as the two areas where I was mainly active. And we tagged them very simply, not very hi-tech, with a big, long pole. This is a beachcaster rod with a tag on the end. Go up in your boat and tag the shark. And we were very effective. We tagged 105 sharks last summer. We got 50 in three days off Inishowen Peninsula.
Half the challenge is to get access, is to be in the right place at the right time. But it's a very simple and easy technique. I'll show you what they look like. We use a pole camera on the boat to actually film shark. One is to try and work out the gender of the shark. We also deployed a couple of satellite tags, so we did use hi-tech stuff as well. These are archival tags. So what they do is they store the data. A satellite tag only works when the air is clear of the water and can send a signal to the satellite. And of course, sharks, fish, are underwater most of the time. So this tag actually works out the locations of shark depending on the timing and the setting of the sun, plus water temperature and depth. And you have to kind of reconstruct the path.
What happens is that you set the tag to detach from the shark after a fixed period, in this case it was eight months, and literally to the day the tag popped off, drifted up, said hello to the satellite and sent, not all the data, but enough data for us to use. And this is the only way to really work out the behavior and the movements when they're under water.
And here's a couple of maps that we've done. That one, you can see that we tagged both off Kerry. And basically it spent all its time, the last eight months, in Irish waters. Christmas day it was out on the shelf edge. And here's one that we haven't ground-truthed it yet with sea surface temperature and water depth, but again, the second shark kind of spent most of its time in and around the Irish Sea. Colleagues from the Isle of Man last year actually tagged one shark that went from the Isle of Man all the way out to Nova Scotia in about 90 days. That's nine and a half thousand kilometers. We never thought that happened.
Another colleague in the States tagged about 20 sharks off Massachusetts, and his tags didn't really work. All he knows is where he tagged them and he knows where they popped off. And his tags popped off in the Caribbean and even in Brazil. And we thought that basking sharks were temperate animals and only lived in our latitude. But in actual fact, they're obviously crossing the Equator as well.
So very simple things like that, we're trying to learn about basking sharks. One thing that I think is a very surprising and strange thing is just how low the genetic diversity of sharks are. Now I'm not a geneticist, so I'm not going to pretend to understand the genetics. And that's why it's great to have collaboration. Whereas I'm a field person, I get panic attacks if I have to spend too many hours in a lab with a white coat on -- take me away. So we can work with geneticists who understand that. So when they looked at the genetics of basking sharks, they found that the diversity was incredibly low.
If you look at the first line really, you can see that all these different shark species are all quite similar. I think this means basically that they're all sharks and they've come from a common ancestry. If you look at nucleotide diversity, which is more genetics that are passed on through parents, you can see that basking sharks, if you look at the first study, was an order of magnitude less diversity than other shark species. And you see that this work was done in 2006.
Before 2006, we had no idea of the genetic variability of basking sharks. We had no idea, did they distinguish into different populations? Were there subpopulations? And of course, that's very important if you want to know what the population size is and the status of the animals. So Les Noble in Aberdeen kind of found this a bit unbelievable really. So he did another study using microsatellites, which are much more expensive, much more time consuming, and, to his surprise, came up with almost identical results.
So it does seem to be that basking sharks, for some reason, have incredibly low diversity. And it's thought maybe it was a bottleneck, a genetic bottleneck thought to be 12,000 years ago, and this has caused a very low diversity. And yet, if you look at whale sharks, which is the other plankton eating large shark, its diversity is much greater.
So it doesn't really make sense at all. They found that there was no genetic differentiation between any of the world's oceans of basking sharks. So even though basking sharks are found throughout the world, you couldn't tell the difference genetically from one from the Pacific, the Atlantic, New Zealand, or from Ireland, South Africa. They all basically seem the same. But again, it's kind of surprising. You wouldn't really expect that. I don't understand this. I don't pretend to understand this. And I suspect most geneticists don't understand it either, but they produce the numbers.
So you can actually estimate the population size based on the diversity of the genetics. And Rus Hoelzel came up with an effective population size: 8,200 animals. That's it. 8,000 animals in the world. You're thinking, "That's just ridiculous. No way." So Les did a finer study and he found out it came out about 9,000. And using different microsatellites gave the different results. But the average of all these studies came out -- the mean is about 5,000, which I personally don't believe, but then I am a skeptic. But even if you toss a few numbers around, you're probably talking of an effective population of about 20,000 animals. Do you remember how many they killed off Achill there in the 70s and the 50s? So what it tells us actually is that there's actually a risk of extinction of this species because its population is so small. In fact, of those 20,000, 8,000 were thought to be females. There's only 8,000 basking shark females in the world? I don't know. I don't believe it.
The problem with this is they were constrained with samples. They didn't get enough samples to really explore the genetics in enough detail. So where do you get samples from for your genetic analysis? Well one obvious source is dead sharks, Dead sharks washed up. We might get two or three dead sharks washed up in Ireland a year, if we're kind of lucky. Another source would be fisheries bycatch. We were getting quite a few caught in surface drift nets. That's banned now, and that'll be good news for the sharks. And some are caught in nets, in trawls. This is a shark that was actually landed in Howth just before Christmas, illegally, because you're not allowed to do that under E.U. law, and was actually sold for eight euros a kilo as shark steak. They even put a recipe up on the wall, until they were told this was illegal. And they actually did get a fine for that.
So if you look at all those studies I showed you, the total number of samples worldwide is 86 at present. So it's very important work, and they can ask some really good questions, and they can tell us about population size and subpopulations and structure, but they're constrained by lack of samples.
Now when we were out tagging our sharks, this is how we tagged them on the front of a RIB -- get in there fast -- occasionally the sharks do react. And on one occasion when we were up in Malin Head up in Donegal, a shark smacked the side of the boat with his tail, more, I think, in startle to the fact that a boat came near it, rather than the tag going in. And that was fine. We got wet. No problem. And then when myself and Emmett got back to Malin Head, to the pier, I noticed some black slime on the front of the boat. And I remembered -- I used to spend a lot of time out on commercial fishing boats -- I remember fishermen telling me they can always tell when a basking shark's been caught in the net because it leaves this black slime behind. So I was thinking that must have come from the shark.
Now we had an interest in getting tissue samples for genetics because we knew they were very valuable. And we would use conventional methods -- I have a crossbow, you see the crossbow in my hand there, which we use to sample whales and dolphins for genetic studies as well. So I tried that, I tried many techniques. All it was doing was breaking my arrows because the shark skin is just so strong. There was no way we were going to get a sample from that. So that wasn't going to work.
So when I saw the black slime on the bow of the boat, I thought, "If you take what you're given in this world ..." So I scraped it off. And I had a little tube with alcohol in it to send to the geneticists. So I scraped the slime off and I sent it off to Aberdeen. And I said, "You might try that." And they sat on it for months actually. It was only because we had a conference on the Isle of Man. But I kept emailing, saying, "Have you had a chance to look at my slime yet?" And he was like, "Yeah, yeah, yeah, yeah. Later, later, later." Anyway he thought he'd better do it, because I never met him before and he might lose face if he hadn't done the thing I sent him.
And he was amazed that they actually got DNA from the slime. And they amplified it and they tested it and they found, yes, this was actually basking shark DNA, which was got from the slime. And so he was all very excited. It became known as Simon's shark slime. And I thought, "Hey, you know, I can build on this." So we thought, okay, we're going to try to get out and get some slime. So having spent three and a half thousand on satellite tags, I then thought I'd invest 7.95 -- the price is still on it -- in my local hardware store in Kilrush for a mop handle and even less money on some oven cleaners. And I wrapped the oven cleaner around the end of the mop handle and was desperate, desperate to have an opportunity to get some sharks.
Now this was into August now, and normally sharks peak at June, July. And you rarely see them. You can only rarely be in the right place to find sharks into August. So we were desperate. So we rushed out to Blasket as soon as we heard there were sharks there and managed to find some sharks. So by just rubbing the mop handle down the shark as it swam under the boat -- you see, here's a shark that's running under the boat here -- we managed to collect slime. And here it is. Look at that lovely, black shark slime. And in about half an hour, we got five samples, five individual sharks, were sampled using Simon's shark slime sampling system.
I've been working on whales and dolphins in Ireland for 20 years now, and they're kind of a bit more dramatic. You probably saw the humpback whale footage that we got there a month or two ago off County Wexford. And you always think you might have some legacy you can leave the world behind. And I was thinking of humpback whales breaching and dolphins. But hey, sometimes these things are sent to you and you just have to take them when they come. So this is possibly going to be my legacy -- Simon's shark slime.
So we got more money this year to carry on collecting more and more samples. And one thing that is kind of very useful is that we use a pole cameras -- this is my colleague Joanne with a pole camera -- where you can actually look underneath the shark. And what you're trying to look at is the males have claspers, which kind of dangle out behind the back of the shark. So you can quite easily tell the gender of the shark. So if we can tell the gender of the shark before we sample it, we can tell the geneticist this was taken from a male or a female. Because at the moment, they actually have no way genetically of telling the difference between a male and a female, which I found absolutely staggering, because they don't know what primers to look for. And being able to tell the gender of a shark has got very important for things like policing the trade in basking shark and other species through societies, because it is illegal to trade any sharks. And they are caught and they are on the market.
So as a field biologist, you just want to get encounters with these animals. You want to learn as much as you can. They're often quite brief. They're often very seasonally constrained. And you just want to learn as much as you can as soon as you can. But isn't it fantastic that you can then offer these samples and opportunities to other disciplines, such as geneticists, who can gain so much more from that.
So as I said, these things are sent to you in strange ways. Grab them while you can. I'll take that as my scientific legacy. Hopefully I might get something a bit more dramatic and romantic before I die. But for the time being, thank you for that. And keep an eye out for sharks.
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They're the second largest fish in the world, they're almost extinct, and we know almost nothing about them. In this talk, Simon Berrow describes the fascinating basking shark ("Great Fish of the Sun" in Irish), and the exceptional -- and wonderfully low-tech -- ways he's learning enough to save them. (Filmed at TEDxDublin.)
Simon Berrow is a marine biologist dedicated to studying and preserving the basking shark. Full bio »