Running the Gauntlet of Global Shark Threats

Tagging a shark is a thrill. Ok, it’s a big thrill. But the thrill doesn’t end when you step off the boat at the end of a tagging trip. The months and sometimes years following tagging a shark is also exciting for researchers as we follow the ‘ping’ journey of our tagged animals. In short, it’s not just the shark that gets hooked.

Reading the latest tag data results is like adding a lost piece to an enormous puzzle. And these days, it’s not just researchers who get to follow along; anyone with an internet connection can experience the excitement of solving this puzzle. One only need follow  OCEARCH to see that people from all over the world can be captivated by the movements of a single shark: Thousands logged on everyday to see if Lydia the Great White would make it right across the Atlantic.

When the 'Ping' hits the fan

But all the science and excitement comes to a crashing halt when your shark is no longer pinging. Although this can happen for a variety of reasons (tags fall off, they foul, batteries die), anthropomorphic threats are high on the list. And while when a tag stops pinging a lot of questions are left unanswered.

Tiger shark track leading up to last pings

But it is most frustrating for a researcher when, as sometimes happens, the track makes a beeline for a coastal port. When a shark’s last ping broadcasts its location in a port or fishing village, there is little doubt that the shark lost its life to fishing pressure.

This really happens. Recently a mako shark, fitted with a satellite tag and tracked across the Atlantic, made consistent final pings from a coastal town in Portugal after last being ‘seen’ in the mid-Atlantic. Likewise, the satellite tag of a great white shark tagged in the cold waters of South Africa’s Cape was found in the toilet in a small village up in Mozambique.

In it for the passion. Photo: RDaly

We don’t become researchers because of the pay checks. We do this job because of a passion we feel, a love for the animals we study. When we know that a fellow human has killed one of these animals, we’re rightly going to be frustrated. We’re going to be sad. And the frustration stems from a number of reasons. 

First, sharks are not naturally vulnerable animals and thus haven’t developed the biological or behavioural strategies necessary to offset high mortality rates. Take tiger sharks for example. They are the top predator of tropical seas and have very little to be concerned about (at least, when they become large enough not to be eaten). They eat, they cruise, they breed – the natural perks of being a large tiger shark. 

Second, when that shark is killed we lose out on a whole lot of data, a whole lot of little pieces of the puzzle that is the ocean ecosystem. 

Third, and tied up in the preceding reasons, there is a great deal of personal and financial investment in wanting these sharks to keep on pinging.

Concern for our Mozambique Tiger sharks

At the beginning of the year, we tagged the first tiger sharks in Mozambique waters within the Ponta do Ouro Marine Reserve. We have tagged 4 tiger sharks so far and as of writing, 2 sharks are still pinging their locations to us. We know very little about how tiger sharks use the ocean, which is why we continue to tag them. From what we and other researchers have observed so far, their movements can be described as showing high individual variability, ranging from regional patrols to long distance migrations.


Tiger sharks have the ability to cover large areas of ocean. Zoe, a tiger shark tagged at Raine Island, in the northern Great Barrier Reef made an 800km round-trip to Papua New Guinea. While at this stage we can only guess the purpose, we do know that these jaunts expose tiger sharks to a wider range of threats occurring hundreds, if not thousands of kilometres away.

Zoe the tiger shark swam to PNG and back - an 800km round trip (indicated by green line).

So what man-made dangers do our Mozambican tiger sharks face in their patrol area?

Artisanal fisheries make up the majority of the
industry in Mozambique Photo: K. Abrantes

Dangers to the north: Fishing pressure

Fishing is vital to the coastal communities in Mozambique. The largest sector is the artisanal fisheries, comprising around 80% of the industry in the country. This sector has no formal reporting system or enforcement, so while difficult to measure, the impact of artisanal fisheries within Mozambique is likely to be significant, with reports of up to 100 000 artisanal fishermen along the coast. This sector is concentrated in near coastal waters with small boats and coastal fishing the primary platforms. This area is also utilised by many species of shark and ray, including tiger sharks. Tiger sharks and other sharks and rays are used for meat, but the shark fin fishery is much more lucrative and is probably driving the expansion of this sector. 

As a rough idea, a 1994 estimate put the total catch of sharks in the artisanal gillnet fishery at 1800T.

Dangers in the open ocean

Tiger shark in the blue Photo: R. Daly

Offshore, industrial fisheries target tuna and sailfish using long lines, with sharks amongst other animals taken as by catch. The level of shark by catch is again difficult to measure due to underreporting. Dedicated offshore shark fin fishing by foreign fleets is known to occur in Mozambican waters. 

Fishing, direct and as by catch, legal and illegal, are clear threats to our tigers and the shark fisheries have grown in recent years – but the extent of the threat remains unknown.

Dangers to the south: Shark culling

Recent tiger shark track (red line) compared with the distribution of KZN Shark Board nets 

Shark culling has been brought to the world’s attention in recent months because of the program set in place in Western Australia. These culls, or shark control programs are designed to reduce the number of large sharks in a local area in an attempt to reduce the chances of unprovoked shark encounters. For our tagged tigers, one of the largest shark culling programs exists to the south and over an international border. The KwaZulu-Natal Sharks Board in South Africa manages a stretch of coastline with shark nets from Richards Bay south 320km. One of our sharks crossed the border soon after tagging and has spent a substantial amount of time in this area as seen in the above satellite track. The shark control program involves a gauntlet of both nets and drum lines. On average, the program catches 51 tiger sharks each year.

Dangers to the east: More shark culling

Photo: MercoPress.com

The KwaZulu-Natal shark nets program has been in place for decades, however new programs are being initiated some distance away. La Reunion has a new program to reduce the bull and tiger shark populations. La Reunion is trialling a multi-pronged approach to reducing shark numbers. Firstly, they are using dedicated fishermen to kill 45 of each bull sharks and tiger sharks (as part of a ciguatera research program). Secondly, a number of long lines with reportedly 300-400 hooks have been deployed and thirdly they are trialling a ‘smart’ drum line program which will likely be extended to cover more areas in the coming months.

Is this really something to worry about?

A tagged tiger disappearing into the deep Photo: R. Daly

Think it’s unlikely a tagged shark could be killed in these ways? Think again. In October 2012, a young Great white shark name Brenda, originally tagged by OCEARCH in South Africa, was caught and killed in Mozambican waters. More recently an immature, Ocearch-tagged great white, Madiba, was caught on a KwaZulu-Natal shark program drum line, less than a year after he was tagged. In this part of the world, tiger sharks and great whites often overlap, using the same waters – the risk is real.

The dangers that await our Mozambican tiger sharks are not isolated to this area. Our research on tiger sharks also occurs with the World Heritage waters of the Great Barrier Reef in Australia. These sharks may head into trouble in the Queensland Shark Control Program. This program, in place since the 1950s kills approximately between 200 and 250 tiger sharks each year along the Queensland coast (178 to 287 per year between 2001-2013).

We can only cross our fingers and hope that our sharks can weave their way through the gauntlet of hooks and nets, and that the pinging continues.


This article was originally posted by our friends and colleagues at Ponta Shark Diaries.