Sharks are in dire straits: how you can help

With many shark species living far from shore and in the depths of our oceans, it can be a case of out-of-sight, out-of-mind. We may think that since sharks have been around since before the rings of Saturn were formed that they can cope with any changes that come their way, but that is not the case. Adam Murphy had a chat with David Sims to discover what's going on...

David - Well, sharks of the open ocean - these are sharks that swim far from land, they live most of the time in the top layers of a few hundred metres, perhaps down to a thousand metres - it's incredible to think that over the last 50 years they've been exposed to high rates of exploitation from commercial, industrialised fishing activity. There's been, over the last 50 years, about an 18 fold increase in the relative fishing pressure. So far and away fishing is the main threat facing sharks. There are other things - habitat loss and pollution - but fishing is the principal thing that we've seen driving down populations.

Adam - And what kind of impact does it have? What numbers of sharks are being pulled out of the ocean by fishing?

David - The numbers are colossal actually. There have been relatively conservative estimates ranging from 63-273 million sharks pulled out of the ocean, so about a hundred million sharks roughly every year. And about 50% of those are pelagic sharks, oceanic sharks. And since about the 1950s, when this industrial scale fishing started to escalate... large vessels, a few hundred tonnes, with refrigeration, navigation, wayfinding equipment as well as sonars, and also very powerful winches and gears. Some of these longliners, for example - they can deploy a longline with a thousand hooks that's a hundred kilometres long, and do that on a daily basis. And there are several thousands of these plying the oceans. So over the last 50 years, we've seen about a 70% decline in oceanic species of sharks and rays. And that's largely because there's a huge overlap between where the sharks like to hang out - where they prefer to be, their preferred habitats - and where the fishers want to be to catch not only sharks, but also tunas and swordfish.

Adam - Let's say the worst happens and all the sharks and their relatives go away. What impact would that have? Why is this such an important issue other than - it's sad that there are no more sharks?

David - I guess people say, "well, hold on a minute, so what if the sharks aren't there anymore?" Well, clearly sharks have been around a very long time, as we've been hearing in the programme, and they're important components of the ecosystem. They're not all top predators; they have really important roles as mesopredators in stabilising the diversity of food webs. And so it's crucial that some controls, more controls than we have had up to now, are put in place to try to allow these populations to recover. So for example, the shortfin mako shark is the fastest shark in the sea, it can swim up to 40 miles an hour when it's hunting and chasing down these different fish species. And what we found with those is that their population in the North Atlantic at least has declined by about 40% over the last 50 years. And as Jenna was saying, the longevity of these sharks, the late age to maturity, is a problem. Shortfin mako sharks don't reach maturity for a decade or more, and they don't have very many young - a female might only have 12 young every three years. So a species like that just finds it a real problem to replace itself, if indeed the exploitation is happening fast enough. There's only a 60% chance of stock recovery by 2070...

Adam - Wow. That is really coming up. And then speaking of going into the future, what about climate change? That thing that always rears its head - what's that going to do for sharks?

David - Change is going to have an impact; not just perhaps directly through changes in their thermal habitat, which may increase ranges of some sharks, but also the interaction with fisheries. So for example, climate change is a major driver of ocean deoxygenation - so this is the ocean losing its oxygen. And this is happening due to the warming of the ocean, changes in the stratification, the temperature profile of water, but also the ventilation. And what we found in our study satellite tracking sharks is that in areas that are losing oxygen fastest, that's reducing the habitat of sharks in the top surface layer as that low oxygen blob of water starts to rise towards the surface. And the fishers actually are able to catch more sharks in these areas because there less water, less volume for the sharks to be in. And so catches a higher in these areas. So in the future, as deoxygenation climate-driven change is happening, it'll interact with fisheries, perhaps to exacerbate some of the population declines we've already seen.

Adam - And this is all very doom and gloom. So is there any cause for optimism to be had?

David - There is, absolutely, there is cause for optimism, because ultimately fisheries and the control of fishing is within our hands. This is something we can solve. And some management actions for these pelagic oceanic sharks have been put in place, but much more needs to be done. And the problem with a lot of pelagic sharks is they're caught incidentally. It could be that the fishing boats aren't really after the sharks; they're after tuna or swordfish, but sharks get caught anyway on these baited hooks. So we've got to reduce the overlap of sharks and these hooked lines if we're to have any chance of recovery, because of that incidental capture. It's very difficult to be specific about which sharks and where you're catching. And there are negotiations at the moment between the UN - or parties in the UN - to have a treaty for the high seas which better protects biodiversity. And spatial management for marine protected areas in certain places where sharks, for example, like to hang out has got to be part of the future solution.

Adam - What about me sitting in here inland in the middle of Cambridge? Is there anything I can do, or other people can do to get involved and help them out?

David - Yeah, there is, there's a number of things on a number of levels. For example, one can be political and start registering views with policymakers, whether that be in this country or for international bodies, the EU and the United Nations. More people thinking about sharks and being concerned about the population declines we've seen is a force for good; that can often lead to change. But I think one of the most important things is education, learning more about sharks. Why is it that many people are frightened of them? And as we've heard in the programme, there are many reasons why we shouldn't have that point of view. And I think also there's a greater opportunity for social engagement, for citizen science. So it's political, it's educational, but it's also scientific; and we're actually launching a project next year as part of our European Research Council funded work which hopefully should allow citizens to actually start to record data from sharks swimming a thousand metres below the surface in the twilight zone, using a small, four centimetre long video camera. So we're asking citizens to look at images that are taken by these sharks as they swim around to see what it is they're encountering way down there, perhaps below where light actually reaches.