Back in 2010, I joined the Marine Megafauna Foundation in Mozambique to study reef manta rays. One of the methods to study these incredible fish is to simply take photographs of them. By one photograph you can often see if it was a male or female, mature or juvenile and even exactly what individual that particular ray is. You see, manta rays have unique spot patterns on the their belly. So by going on dives and taking photos of the underside of any manta ray you encounter you can, over time, start to get an idea of population size, population structure, and possibly even movement and residency patterns.

MantaThose spots can tell us which individual it is


But…. In the vast ocean we are somewhat limited as primarily land-based creatures. Using regular dive equipment you may be able to spend 1 to 2 hours effectively underwater per day. And of course, you can’t survey multiple dive sites at the same time. After spending 6 months in Mozambique, I returned to Holland and started thinking if there isn’t a more effective way of collecting the same, or more, data.

DiverLobo No matter how much we are enjoying it down there, we can’t stay forever


For terrestrial species, photo-identification as it is known, is also often used. And by using so-called camera traps, you can survey multiple areas for extend periods of time. These specialized cameras turn on when something passes in front of it, only taking photos or a short video when it is needed, and conserving precious battery life otherwise. They can be deployed for weeks, months even.

To sense anything passing by, a sensor is needed. In conventional camera traps this is most often either a passive or active infrared sensor. So I thought, why not use this underwater?! Put one of these camera traps in a housing, put it on a reef, leave it there for a couple of weeks and pick it back up and see what animals, particularly manta rays in my case, have swum by.

If only things were this simple…. These infrared sensors, however, do not work underwater. Infrared light in an aqueous environment simply gets absorbed too quickly by the denser water. So what would kind of sensor can work in the salty sea? There are may number of possibilities, some more practical than others.

A friend of mine suggested using the fact that a large animal swimming over will cast a large shadow. Sensors that sense sudden light changes are readily available. So I started working on this. After a lot of google searching and some tinkering, this was the result. Two days before I was to leave again for Mozambique, and with the help of a good friends dad, we even made an underwater housing that would fit all of it in.

CT1After a lot of tinkering, soldering and perhaps also swearing, underwater camera trap 1.0 emerged


Did it work in real life scenarios? Not really. Light diffuses quickly underwater, and unless the water is clear like gin and the sun is out, the shadows created by large objects aren’t harsh enough to trigger the sensor. And it obviously could never work at night, or when it is not pointing upward towards a light source.

CTDeployedThe first ever deployment, unfortunately we came up empty handed


You could also set up a laser (not infrared) possibly on one side and align it with a light sensor on the other, and if anything breaks the laser it sets off the camera. But good luck putting all those different components in underwater housings and keeping the laser and sensor aligned in the often quite volatile ocean environment.

Sonar is a distinct possibility. Sound waves get sent out in pulses, and anything that it bounces off of will get picked up by a little microphone and voila, the camera takes a photo. But sonar also eats away at battery life and in reality is a lot more complicated than it sounds. And most readily available sonar components still emit at a frequency that some animals, such as cetaceans can still hear. To me, it didn’t seem like the solution.

So what next? Could you not combine lasers with sonar (evil scientist anyone?)? What if, instead of sound, you emit laserlight pulses? And if these light pulses bounce back off of anything, it gets picked up by a light sensor, in the same housing as where the camera and laser is? No tricky sonar or alignments of lasers needed! Could it possibly work?

I started scouring the internet and soon found components that might be suitable. With a lot of mucking around trying different things, I got something that worked. On land at least. With help from a friend, Ando Shah, also working at the Marine Megafauna Foundation, we improved the software and overall size of the device.

CT2.0Underwater camera trap 2.0: lasers, laser sensor and camera module all in one small package


We did pool tests, and it looked promising. Objects from two meters away were being sensed by our sensor. But would it work  on a reef system 25 meters deep?

AndoPool_I8A5214Preliminary tests in the pool proved promising. Here is Ando taking notes


In short, we don’t know yet. Turns out, electronics are not a big fan of a salty air environment. Nor do they like to be accidentally short-circuited, which does tend to happen when tinkering with a bunch of wires, lasers, cameras and batteries. Every time we had a working prototype, something would go array shortly after. And unfortunately, tiny specialized electronics are not easy to come by in Mozambique…. I once had to wait more than 6 months for a new camera module.

So it is still very much a work in progress. But I am confident that it will work one day. Could it  be used only for the benefit of manta rays? No. It could be used for anything really.  Document interesting behaviour in the deepest of seas? Assess biodiversity in remote areas? Help conserve aquatic species threatened with extinction? Perhaps this little device could do it all. Only the future will tell.


We got excited when we heard there was a satellite tag, which was until recently attached to a great white shark (Carcharodon carcharias).  Somehow it had made its way onto Mozambican soil. We had been contaced by Alison Kock, research manager at Shark Spotters; she was receiving transmissions from outside a town called Chidenguele, about a three hours drive south from Tofo.


The transmissions of the tag were close to the main road, so we were confident we could find it


Having printed off some flyers and put the last transmission locations into our GPS, Clare and I set off in my rusty 4×4. After several detours, we arrived at the end of a road only 600 meters away from the last transmission and could not drive any further. We parked near a village and started asking around in our best Portuguese. One guy seemed adamant he knew where the tag was and gestured to follow us. Only problem was, this friendly fellow could not talk. All he could do was emit high-pitched squeals and frantically gesture for us to follow him.


Silent Guy_FI8A5088

Our self-appointed guide for the day


He was going in the opposite direction of the last transmitted tag locations, but knowing these locations are not always accurate and due to the sheer enthusiasm of our newfound friend, we followed on. He led us around for about 2 hours passing many villages, passing out flyers with my phone number, a picture of the tag and explaining to people what we were looking for.


Pointing Guy_FI8A5075

“It is just over that hill!”


We were starting to lose hope and were about to head back to the car. Disappointed, thirsty and drenched in sweat, we handed out the last of the printed flyers to a group of women carrying water back to their village.

A short woman wearing an orange t-shirt suddenly started jumping up and down and cheering. We shortly joined in the celebration as she said she had found the tag on the beach. We were dancing around high-fiving each other. Our murmuring friend grabbed my wrist and raised it in the air as if I had just won the century’s greatest boxing match. Everyone was overjoyed.



Some of the curious onlookers as we were trying to retrieve the tag


We all went back to her village, a mere 220 meters away from the tag’s last reported location. The chief was called and we asked if we could see the tag. Everyone went off to a strange pile of dead palm leaves about 50 meters away from the houses and started digging away. When I approached the digging site, I got a sudden “espere!” (wait!) from the village chief.

I was a bit baffled and hesitantly stood at about 20 meters away waiting to get permission to come closer, take a few photos and help with digging. I soon found out the reason why I was told to wait; this wasn’t an ordinary pile of palm leaves, it was their toilet. And the tag was somewhere in the midst of it.



The ‘tag storing facilities’, also known as a ‘toilet’


After about 10 minutes they started walking back and washing something in a bucket of water. We were eagerly waiting to see if it was the actual tag, a bit anxious of its state as well… after all, it had been in a dugout hole full of human faeces.


Tag People_FI8A5085

The vast amount of data stored on this tag will aid in white shark conservation


After a quick rinse they held it up. It was the tag, fully intact at that. We quickly settled on a reward price of 700 Meticais and swiftly found a bag to keep the tag in. The tag will be sent to Alison in South Africa, and will allow for detailed analysis of all the archived data. We hope this tag will help unlock some of the secrets of one of nature’s greatest predator, the great white shark!