Using shark tags as ‘theft alarms’

The loss of acoustically tagged sharks in a Marine Protected Area (MPA) have been shown to overlap with illegal fishing activity. Could electronic tags be used as ‘theft alarms’ to prevent the practise in the future?

A grey reef shark, one of the study species in the paper

A paper published this week in Animal Biotelemetry has shown that the sudden loss of tracking data from sharks in the British Indian Ocean Territory’s MPA is linked to the discovery of illegal fishing activity on the site. Patrol vessels found over 300 sharks on board the illegal fishing vessels but using the tracking data researchers think that number could be closer to 2000. The team behind the paper suggest that electronic tags could be used as a means of locating and accurately predicting illegal fishing of sharks and other high-value species. The illegal trade of sharks has led to serious overfishing of some species and is the main threat to their survival. What makes it so hard to tackle is that it is nearly impossible to monitor vessels and accurately assess how many sharks are taken. Equipping sharks with specially adapted tags could be the best way to combat the issue and conserve population levels.

Original project


The team of researchers behind this new paper are led by David Tickler from the Centre of Marine Futures at University of Western Australia. In 2014 they conducted a study on the spatial movements of two species of reef shark in an MPA in the British Indian Ocean Territory. To do this they used a method called acoustic tracking where electronic tags are surgically inserted into the animal which is then released to swim around the target area. Within the target area a relay of acoustic receivers are spaced out evenly and when a shark swims by one of those receivers it retrieves data from the shark’s tag in the form of sound. This data contains things like depth, temperature and acceleration and can all be used to better understand the animal’s behaviour. In total 47 grey reef sharks and 48 silvertip sharks were tagged and used in the project. Now the data from their study has been used to highlight a potential new use for this technology.

The acoustic receivers used in the project

Loss of signal

What made the team re-evaluate the data for this study was not the tracking data they managed to retrieve but the tracking signals that they lost. There are a number of reasons why the tags may have gone dark. Firstly there are some occasional technological problems that can occur such as receivers not properly picking up signals or tags running out of battery. Signals can also be lost due to predation, by larger sharks such as hammerheads, or other forms of mortality such as illness or old age. Finally there is always the chance that the individual migrated outside of the target area, even though reef sharks show high site fidelity and very rarely traverse the open ocean. However despite these reasons it was still very unlikely that more than a couple of tags would be lost each month. But during December 2014 the team lost a total of 15 signals from shark tags. This was a tag loss rate five times higher than any other month and was unlikely to have happened by chance.

Fishing overlap

What the team realised was that the period of increased tag signal loss overlapped strongly with increased illegal fishing detection in the area. Patrol vessels belonging to the MPA intercepted 17 ships suspected of illegal fishing in December, the same month the 15 tags went dark. Two of those ships were arrested with a total of 359 sharks on board, of which 47% were grey reefs or silvertips. But based on the percentage of tag loss and population data the team had collected they calculated that the number of sharks lost in that month was likely to be nearer 2000, with at least a half being grey reefs or silvertips. They estimate that up to a third of the locally resident reef sharks may have been removed from the MPA. This is apparently still going on because researchers that continue to work in the MPA also received a tag from a fishing market in Sri Lanka as recently as 2018.

Pacific Sharpnose Shark Longline
A shark is trapped in a pelagic longline, the most common form of illegal hunting

Adapting the tags

The researchers say this example is representative of how even sporadic fishing can have serious effects on shark populations. But also point out it ‘demonstrates the potential of electronic tagging as a tool for detecting illegal or otherwise unreported fishing activity’. Using acoustic tags to monitor MPAs is a good way to assess the impacts of illegal fishing but given some improvements they may also be able to help catch the criminals red handed. One such improvement is FastLoc GPS which is used to track things such as cetaceans and turtles. It works by sending location data immediately to the nearest satellite when these animals surface to breathe, it is not as accurate as regular GPS but is much quicker. Sharks are not normally fitted with these tags as they very rarely surface, instead acoustic tags are more effective. However if their tags included FastLoc GPS they could send a signal to authorities as soon as they are removed from the water by fishermen. Therefore they could act as a theft alarm system and give us the best chance of catching who took them.

Satellite tracking of animals has been done for many years now and has helped produce fantastic research in spatial ecology and behaviour. But innovative new ways of using satellite tracking like this are starting to become more common. In October 2018 a multi-national operation by Europol codenamed Tarantelo caught 79 suspected illegal tuna smugglers by tracking their phones and tablets rather than trying to track their boats. As a result they recovered 88 tonnes of illegal bluefin tuna and helped to break a smuggling ring. It’s also not just illegal fishing, recently a team led by Evan Mason from University of Washington tagged seabirds to measure ocean currents. This creative project tagged 75 Scopoli’s shearwaters and used them as feathery buoys tracking how they moved as they rested on the ocean’s surface. New technologies and creative ways of using them such as these will hopefully be very useful in solving problems in the future.

A Scopoli’s shearwater doubles up as an ocean current buoy

Is the MPA working?

This is a hard question to answer, in a sense no because illegal fishing still occurs but also yes because it still aids in conservation efforts. The real factor in the success rate of MPA’s is enforcement. Reserves such as the British Indian Ocean Territory often cover hundreds of thousands of square kilometres and patrolling and monitoring them can be hard and expensive. As well as this the punishment for illegal activity varies widely depending on the governments of the country an MPA belongs to. In some developing countries officials turn a blind eye to things like illegal fishing or do not have the money to fund proper enforcement. However even though MPA’s are not perfect they are still important for marine wildlife conservation. In this study if the MPA did not exist the researchers would not have been able to set up their acoustic tagging project and would never have been able to find out what they did. Rather than give up on MPA’s it is important to continue to try and improve them and technology like ‘theft alarm’ tags could go a long way to doing that.

To sum up

The removal of reef sharks, such as silvertips and grey reefs, can have serious implications to their ecosystems. They are top predators and without them delicate coral reef systems, already under pressure from factors such as coral bleaching, can be seriously damaged. The same is true of other species of shark and other top predators like whales and dolphins, many of which are already threatened. That is why illegal fishing is such a damaging practise and stopping it is of the upmost priority. It is now believed to be the 6th most profitable crime in the world and due to its nature is very hard to tackle head on. But technological advances such as FastLoc GPS and monitoring projects like the one in British Indian Ocean Territory’s MPA can be used to level the playing field.

Reef sharks play an important role in coral reef ecosystems

However it must also be considered that tagging marine animals is not without risk, especially when surgery is required, and so care must be taken if the number of individuals being tagged increases. It is also not the only way of fighting illegal fishing. Unfortunately in developing countries the practise is a way of making money for people who have very little and need to provide for their families. So whilst it is easy to stereotype illegal fishing as a cruel and unnecessary activity it is also important to remember it is some people’s way of life. Therefore whilst promising tracking advances such as the ‘theft alarm’ shark tags should be explored, time and effort must also be spent in trying to tackle some of the core economic factors behind the problem.

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