Global risk assessment of sharks under the footprint of fisheries

Being a part of the largest global shark tracking programme in history.

Oliver Jewell Continue

Sharks under threat

Anyone that works on the ocean, or anywhere else in the natural world for that matter, knows we’re facing a growing dilemma. The footprint of human development is everywhere, we’re losing biodiversity faster than ever, and our natural resources are becoming strained. Combine this with the additional human-made pressures of global climate change and pollution, and you can see where I’m going. In the ocean, a huge issue is industrialised fishing, particularly in the high seas (areas outside of national jurisdiction). This study sought to determine the overlap in global fishing pressures, with the movement of as many elasmobranch species as possible.

A white shark carrying a newly deployed SPOT tag in Gansbaai, South Africa. The shark was tagged during the 2012 Ocearch campaign to South Africa and later contributed the Quiroz et al. (2019) Nature paper.

So how do you go about doing that?

Well, I’ll start with the tracking, as it’s the world with which I’m most familiar. In the late ’90s, researchers placed the first satellite tracking devices on elasmobranchs. One of the first species to carry them was, of course, my favourite, the white shark.

A team from California, including good friends and colleagues Andre Boustany, Scot Anderson and Barbra Block, tracked the movements of a white shark from the Farallon Islands to Hawaii [1]. The discovery was a complete game-changer because previously people thought that the species was primarily coastal.

The study didn’t say ‘everything you know about white sharks is wrong’ but was certainly a ‘there’s way more to the picture than you realise’ moment.

Later, studies found white sharks could migrate from South Africa to Australia and back [2] and the existence of an offshore aggregation in the North East Pacific [3]. And that’s just in the one species!

Since then, more and more people have been using these types of tag on elasmobranchs. There are mainly two types of tag design; Smart Position Only (SPOT), that attaches to the fin and transmit at the surface and Pop-off Archival (PAT), that logs data and pops to the surface to transmit afterwards. They’re both written about in our tagging and tracking shark’s page.

Our South African contribution

For years people were fascinated by the South Africa to Australia discovery, which was made by a shark named Nicole. She was tagged, and later photo ID’d right off Dyer Island, where I conducted my Master’s research and spent many years guiding ecotourism trips with Marine Dynamics.

People wanted to know if other white sharks made this migration.

The problem was, the tags were expensive and financial resources in South Africa are limited. That didn’t stop us from doing some great research, but it did stop us from trying to repeat that study. Then along came an organisation called Ocearch, who you may also know from the TV show Sharkmen.

They wanted to collaborate with us, all those studying white sharks in South Africa, to satellite tag and understand the movement patterns of the species across the Southern African region.

Now, their arrival wasn’t without controversy, their TV show had been divisive, as it depicted the removal of large white sharks from the water to be fitted with satellite tags before release. And this is a process that’s neither pretty nor easy to watch. But it does allow a great deal of information to be collected on the animals before they head back to the water.

Some local stakeholders in shark ecotourism were against the expedition because they felt their businesses might be affected or that we may hurt the sharks. These opinions were understandable, and we had to address them thoroughly before we began work. We had multiple stakeholder meetings and a huge amount of my time during this expedition was spent walking around Kleinbaai having face to face meetings with the cage diving operators. After all, this was the community I lived and worked in, and these were the people (and sharks) I worked with every day.

The point I must emphasise is, that our (the scientific community and government) decision to go ahead with this expedition was that, although we did a lot of local research, we were missing critical information on the migration patterns of the species. And if you don’t know enough about where a species goes, it becomes difficult to protect and manage it.

This was a critical opportunity to gain the information we desperately needed.

The Ocearch team arrived with their vessel, the RV Ocearch, the two types of satellite tag, 10-year acoustic monitoring tags and a host of other research equipment. They divided their time into two trips, one to the east from Mossel Bay to Port Elizabeth, and a second to the west that would focus on Gansbaai, False Bay and the surrounding area.

Each area had a lead scientist or two, in Mossel Bay, this was Ryan Johnson and Enrico Gennari, in Port Elizabeth this was Malcolm Smale and Matt Dicken, in False Bay, Alison Kock, and in Gansbaai, it was Alison Towner and I. There was also a vet, Pieter Koen, and a representative from the Department of Environmental Affairs, Mike Meyer, onboard during all research times.

The plan was to move from area to area to maximise the shark catching opportunities without putting too much pressure on one spot. Fishing would take place over a few days at a time. Sharks would be hooked, brought aboard the platform and fitted with a SPOT and an internal acoustic tag each and in some cases an additional PAT tag to validate positioning and give us depth data.

PAT tags leftover at the end of the expedition would be divided between regional researchers, and spare SPOT tags were to be used on tiger shark or bull shark research. Blood, parasite and bacterial samples were also taken from sharks while transmitters were being attached. And several ragged-tooth sharks were also caught and tagged while the team were in Port Elizabeth.

The expedition was a huge success. We caught 37 white sharks in total between the sizes of 2 and 5 meters in total length. We caught 16 in Gansbaai alone. And I got to use one of the additional PAT tags to track the movements of one of my all-time favourite sharks, Nemo.

And this was just us in South Africa. Across the world, other scientists were running similar expeditions and a huge amount of data on shark movements and migrations was being generated.

Our results are part of several studies that will be available in the coming years (some are already out). Yet when we were contacted by Professor David Sims of the Marine Biological Association about joining our datasets with others to create a global shark tracking project, we, of course, said yes.

And that brings me to the second part of our story, industrialised fishing.

A white shark in Gansbaai being fitted with a SPOT tag aboard the Ocearch tagging platform. I'm the guy at the back with the cap and black jacket deciding which sample to take next.

I got to tag Nemo, who was a favourite shark in Gansbaai, with a couple of missing fins, shortly after the Ocearch campaign with a PAT tag. She took this tag all the way to waters South of Madagascar in about 8 weeks and then returned to Gansbaai another 4 weeks later. An incredible migration by a shark we knew so well but had no idea how far away she went.

The total distribution of white sharks in the Southern African region from sharks tagged during the 2012 Ocearch expedition. Tracks from our data ranged as far as the Chagos Archipelago, a group of islands closer to India than South Africa, and waters near the Prince Edward Islands, remote islands about halfway between South Africa and the Antarctic. We did not find another Nicole in our research but uncovered many other unforeseen migration routes.

High Seas Fishing

As human populations grow, there is inevitably more pressure on natural resources. This causes complex issues between managing resources so that they last while ensuring the growing communities are healthy. And with fish, this means feeding people without crashing fish stocks.

Worldwide, an estimated 16% of the protein in people’s diet comes from the sea [4]. As we get closer to a global population of 8 billion, there’s inevitably going to be more of a strain on our oceans, which is why managing fisheries is such an essential but challenging job.

Quotas have to get things right. Not only are fishing communities destroyed by a crash, but the ecosystem may be irreversibly damaged as well.

One of the most famous examples of this was the Cannery Row sardine collapse, in Monterey.

Managing fisheries on a local-scale isn’t easy. Yet as vessels often return to local ports, catches can be monitored. If necessary, coastguards and navy’s can also assist with fisheries enforcement. Today, there are many success stories for locally managed, sustainable fisheries (i.e. pole and line caught skipjack tuna in the Maldives). What’s more, there’s a growing awareness of making an informed decision on what fish to buy from a consumers perspective (see Monterey Bay Aquarium’s Seafood Watch, for instance).

Things aren’t perfect, but steps are being made. However, there’s a bigger picture to consider.

High seas fishing is defined as fishing outside of any nations’ exclusive economic zone’ (EEZ), typically 200 miles offshore of the coast. Although as you may have read in the news in recent years, there are some pretty major political disputes about what is and what is not considered certain nations’ coastlines, and subsequent EEZ’s.

High seas fishing is controversial because there are little rules and regulations are governing what can and what can’t be caught. Sure there are protected species acts and organisations such as the International Commission for the Conservation of Atlantic Tunas (ICCAT). But this is just one fishery and specifically designed to manage the catches of one type of fish.

A recent example of how controversial high seas fishing can be is occurring right now off the Galápagos Islands, part of Ecuador. The island group were declared a UNESCO World Heritage site in 1978, and have been a great example of conservation success. But outside of the limits of Ecuador’s EEZ, waters are no more protected than anywhere else, and there are currently around 260, mostly Chinese, high seas fishing vessels sitting right on the edge of that limit.

Monitoring of where and when high seas fishing was occurring was nearly impossible until recently. Global Fishing Watch is an independent not-for-profit organisation put together with the aim of monitoring the world’s fishing effort [5]. It all started with a collaboration between Oceana, Sky Truth and Google, and I highly encourage you to take a look around their site for more information.

You can live view fishing vessel concentrations, or look back on historical records at the click of a button, and here’s a couple of maps I made in just a few minutes on their site.

Fishing vessels often use automatic identification systems (AIS) for safety and management. Here you can see the large concentration of fishing vessels right on the edge of the protected waters of the Galapagos Islands.

A similar, but less concentrated concern, are the high seas off South Africa, Mozambique and Madagascar, where a lot of the white sharks we tagged frequent.

Putting the pieces together

We were now in a situation where for the first time, we had enough data to explore the movements of many shark species in many regions of the world and a way to monitor fishing pressures the sharks encountered along the way.

Putting this all together would be no easy task, though. Lead authors, Nuno Queiroz, Nick Humphries, David Sims and their colleagues had now amassed 1,804 datasets from 23 species and four of the world’s oceans. Putting this data together raw is a challenge alone, but these datasets also require a fair amount of processing before they are usable too. Together with the groups actively making the deployments to wild animals, there were now over 150 people working on this project.

An overview of all the shark species tagged and tracked in the study. Over 150 authors made painstaking contributions to the collection and processing of this global dataset.

Worryingly, once you compare both datasets, it’s easy to see there is considerable overlap between shark movements and high seas fishing fleets. Around one-quarter of the month-by-month movements, meaning there are few safe havens for sharks in the open ocean.

And this situation gets worse when you focus on two of the most exploited species, blue sharks and shortfin makos in the North Atlantic, that were spending an average of 76% and 62% within overlapping areas.

Threatened species weren’t far behind, with white sharks and porbeagles some of the next most at risk with over 50% overlap.

“Our results show major high seas fishing activities are currently centred on ecologically important
shark hotspots worldwide” said Professor David Sims, head of the Global Shark Movement Project in the Marine Biological Association press release for the study.

A further worry was that fishing pressures overlap almost all ‘hot spots’ of shark activity. These hotspots indicate where critical habitats for sharks are, often including foraging grounds, in some cases even mating or nursery areas.

The overlap in hotspots is an additional concern because these fleets may not only be reducing shark numbers by their catches, but they may also be removing breeding stocks, which inhibits the ability of species’ caught to rebound. Without changes, the future may be pretty bleak for sharks.

As Professor Sims put it “Some of the shark hotspots we studied may not be there in as little as a few years’ time if management measures are not put in place now to conserve the sharks and the habitats on which they depend.”

Fortunately, it may not be too late. The United Nations are currently discussing how best to manage the high seas in future as part of the UN Ocean Conference, with the ultimate aim of updating the High Seas Treaty. Some proposals have already suggested that 30% of the high seas should be designated protected areas, and this study will provide substantial evidence in support of this.

Unfortunately, due to Covid-19 wreaking havoc across the world, the meeting has been delayed. Yet there’s still hope that decisions may be made later in the year or early in the next, setting the wheels in motion to protect sharks in the high seas.

The extent of overlap between the sharks and fishing vessels tracked. The yellower/whiter the distribution, the greater the density of overlap. Blue circles indicate where tracked sharks were caught and killed, mostly by commercial fishers. Two of the white sharks we tagged and tracked were killed but both were in inshore areas. Another study is needed to highlight the threats sharks face closer to shore.

The Legacy of the work

This is the most comprehensive work so far to overlay where sharks go and where they are under threat. Yet there are still limitations in the risks we can describe. Most of our data came from 11 species of shark, and there are far more species under threat globally. We can only tell hotspots from areas where sharks have been tagged, and there are large gaps. Barely any sharks have been tagged in the South West Atlantic or off East Africa, and across Asia, there are huge regions where no sharks have been tagged, for instance, off of India.

Likewise, only between 50 and 75% of large fishing vessels have AIS transponders and can be mapped using these methods [6]. The true fishing effort and the true overlap in shark movements will be even greater than we can describe.

But this is a substantial first step in describing the challenges ahead in high seas management. As Professor Julia Baum concluded in her review of the study, “Querios et al. have provided a much-needed blueprint for conservation actions that could be used to provide sharks with safe havens in our increasingly crowded oceans” [6].

Stay tuned for future studies or check out for more information.