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.
Those 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.
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.
After 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.
The 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.
Underwater 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?
Preliminary 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.