A little while ago, you may have read my blog post on ‘the challenges of saving ocean giants (part I)’ describing some of the underwater challenges that make marine research, well, challenging.

You want to find out where your large, far-roaming, pelagic animal goes. Following it around is just not feasible due to low underwater visibility and the fact that humans are simply not made for being submerged for long periods of time.  Luckily there are a number of technologies that might just do the trick for you.

Tags allow for the identification or even tracking of individual animals. In the past, researchers wanting to know where a fish species, for example Bluefin Tuna, roamed, would catch them, quickly put a little plastic tag with an ID-number and contact details, get some basic information such as size and weight, and throw the fish back. By working closely with fishermen, hopefully in the next few weeks, months, perhaps even years, someone else would catch the same fish, see the tag, and contact the researchers, providing valuable information such as migration paths and growth rates. One great example of this is an Atlantic bluefin tuna tagged at two years old and just 14 lbs in 1997, which was caught again after sixteen years, now weighing in at a whopping 1,200 lbs!  But obviously you won’t be re-catching all the fish you tag, so you have to put out an awful lot of tags to get a decent amount back.

Nowadays, there are electronic tags, and they don’t necessarily need to be retrieved to get your data. Two common methods are acoustic telemetry and satellite telemetry. For the acoustic tags to work, you need to put out an array out of acoustic receivers, or ‘listening stations’. These stations listen out for an inaudible acoustic signal that the tags emit every minute or so. By downloading the data stored on the stations, we can see which tagged animals have been around.  And you can do this long-term. If you have a way of attaching the tag securely to the animal, or performing minor surgery and fitting the tag inside the animal (such as the abdominal cavity), you can monitor the animal’s presence near listening stations as long as the tag’s battery last. And this can be long, as long as five years.


actagThe acoustic receiver on the left listens out for the acoustic tags (seen on the right)


But you can only see if the animal is present in places where you put your stations, and of course the marine environment isn’t going to make it that easy. Environmental noise caused by waves or other organisms (such as snapping shrimp. Yes, you read that right, tiny little snapping shrimp) can produce so much noise that the listening stations cannot hear the acoustic tags properly. You also have to contend with all sorts of marine organisms trying to make the listening stations or tags their home, covering every inch of them.  Swell and strong currents might make your stations do a little travelling by themselves, leaving you without the device and, even worse, the data stored on it. 


taggedmantaA reef manta ray with an acoustic tag


Enter satellite telemetry: You aren’t dependent on other devices such as listening stations, and you can track the animal’s day to day movements as well as its depth and the temperature of the water it is in. These sophisticated tags archive data every 30 seconds to several minutes or so for several months, maybe even a year. After this pre-programmed period the tag pops off the animal and transmits daily summaries of all this information to an online database through the ARGOS satellite system. Pretty neat, hey?! 



A pop-up satellite archival tag, or ‘PSAT’


But again, there are still challenges to be overcome. GPS does not work in the underwater realm so we have to do with simpler, cruder ways of getting a daily position of the animal. Noontime shifts as you move around the earth longitudinally.  The length of the day gets shorter or longer dependent on the time of the year as you move between the equator and the poles. So you can estimate daily longitude and latitude by recording light levels. This all takes quite a bit of computing however, once you get the transmitted information, as it is all dependent on time of the year as well. And light levels aren’t always accurate, as marine mammals tend to dive up and down quite a bit, resulting in inaccurate light level readings. Recently there have been more accurate ways of telling latitude by looking at geomagnetic levels of the earths crust, which can give much more precise latitudinal positions.


Tagging_I8A4325Deploying a satellite tag on a reef manta ray in southern Mozambique


The data you get through the ARGOS satellite system is only a daily summary of the archived information. If you are lucky however, you can find them back. For my studies on reef manta rays I have been lucky enough to do so and you can read about it here!


taggedManta_I8A4301A reef manta ray with a fitted satellite tag


And of course there is the matter of biofouling, the growth of marine organisms on the tag, and tag retention. Any biofouling happening on the tag attachment might cause the tag to remain attached to the animal when it is supposed to pop off to transmit all it’s archived information.  If this happens, you might never hear from your tag again! Tags also occasionally tend to get eaten. Resembling a little fish swimming alongside your tagged manta ray, whale shark or great white, other predatory fish might gulp it up. And as these devices tend to be several thousands of dollars, this is obviously not something you would like to happen!

 As technology progresses, we will likely have better ways of tracking the movements of ocean giants. But as for now, we will have to do with the current options.

* Written by Daniel van Duinkerken. This post was originally posted on


Imagine doing behavioural research on a population of lions on the beautiful plains of the Serengeti. Your aim is to find out where they go. Why? You want to preserve them for future generations. One major implication in protecting an animal, is knowing where they go. If you want to protect and conserve any animal, you will need to know some things about how they go about their everyday life. You need to know ‘what’ the animals are doing and ‘where’. Where are they migrating, feeding, mating and giving birth? And different animals in a population might have different agendas, so it is also important to know what the subgroups, such as males/females/young/adults, are doing similarly, or differently. After all, if you are trying to save a species from extinction, you will not only need to protect one small part of the population. What use is it if you are protecting an area which only males frequent, while the females might be dying off elsewhere? Or if you are only protecting their mating grounds, but not their feeding grounds? 

Who wouldn’t want to follow these guys around all day long?


 Each morning, you get up before sunrise, go out into the vast African plains in a rugged 4×4 vehicle, to find the lions. You find tracks to follow or listen to the majestic roars bouldering across the bushveld. After locating the lions, you patiently observe and follow from a safe distance, trying not to disturb their natural behaviour. You work long hours, and get amazing data on where the different prides hunt, rest, mate, where the females go to give birth and where the bachelor males wonder to. If you keep this up for quite a while, you might be seeing yearly patterns. Prides moving north in the winter, south in the summer, following migrating prey.  This all sounds amazing, but also quite the feat to find out, isn’t it?

 Now imagine that same lion population living in an area with extremely dense fog. On the very, very best of day you might be able to spot an animal 30 meters away. On bad days you might happen to stumble upon the lions when you are only 3 meters away. And then just imagine that these are quite odd lions that leave no tracks or emit any sounds to follow or record. And these lions also need to continuously move, there is no resting or sleeping, making it harder for you to find and catch up to them. To top it all of, these lions also live in an environment where you, as a human, can only spend a few hours a day. If you exceed these limits, you end getting sick or possibly even die.

 This gives a clearer picture of what it’s like to study far-roaming pelagic animals. Manta rays, whale sharks, billfish, great whites; they all live in places and have habits that make it incredibly hard to study them.

MurkyManta_I8A7170When the water is like pea soup, these guys might be swimming right by you and you wouldn’t even notice!


 It is probably quite obvious by now that these animals are quite hard to get your head around. You can’t jump in the water with a SCUBA tank strapped to your back and go trailing a manta or whale shark all day. It is simply impossible due to issues such as decompression sickness, fatigue, cold and obviously the somewhat thicker nature of water compared to air. You cannot follow the animal everywhere. Would you like to swim down to several hundred meters depth, or over a kilometre deep? It would mean certain death. If you do decide to follow your research subject, you are also quite likely influencing the animal’s normal behaviour.  How would you feel if someone was trailing you for hours, maybe even days on end, from only 30 meters away? And remember, that 30 meter figure, is on a good day. And you can really only follow one animal at a time, so it will take you a long time to figure out what the entire population is doing.

Tagged Manta_FI8A5180Can you see that little antenna sticking out? These sophisticated tags allow us to track these large pelagic animals


 Fortunately, devices have been developed that can help see where animals, both terrestrial and aquatic, go. Perhaps a simple way to study the movements of your pride of ions would be to attach a small GPS device onto an animal, leave it on for as long as the battery allows, then find the animal again, get the GPS back and download the data, which should give you quite precise information on the animals whereabouts. But, you have to find the animal again to get the data. And you would have to design a GPS device that is small and light, battery-efficient, super robust, able to withstand prolonged exposure to water, heat, rubbing up against stuff, moving around and so on.

 For marine animals, it doesn’t get any simpler. For starters, there are few habitats that are more hazardous to scientific equipment than the marine environment. Corrosive salt water and bone crushing depths come to mind. Add to that that GPS doesn’t even work underwater, and once again, the marine environment is presenting us with quite a few more challenges.

 So how do we try to overcome those challenges I hear you ask? I will leave that for my next blog.

* Written by Daniel van Duinkerken. This post was originally posted on



Ecstatic is the right word to describe how we felt after deploying five pop-up satellite archival tags (PSAT’s) on reef manta rays early July. The first ever PSAT’s to be set on reef manta rays on the continent of Africa, these sophisticated devices were programmed to stay on the animals for approximately 100 days, collecting a wealth of information on the reef manta rays’ movements and diving behavior.

Tagged mantaA reef manta with a satellite tag


I have been diligently checking my ARGOS satellite account for any hits every day since the tags were first deployed. These tags are only able to transmit when at the surface, so when the animal is in or in the unlucky event that a tag has shed prematurely. Not expecting any hits until the tags were programmed to pop off on the 10th of October, it was a bit of a disappointment to find a steady stream of hits of one tag after only 19 days! And another tag started transmitting only after 36 days on the animal. My ecstatic state was quickly turned into a somewhat disappointed and panicked demeanor.

ARGOS_IMG_4184A steady stream of hits from the ARGOS satellite system most likely means a tag has popped-off, as was the case with tag 128924


These tags are highly advanced, and this means a hefty price tag. With each tag having a total cost of around US$3500, you want them to perform well and get the most out of them, especially as the chances of seeing them ever again is pretty slim. The positions we get from these tags when floating at the surface are not that accurate, with errors of at least several 100 meters, making it quite literally looking for a needle in a haystack when it is bobbing around in an immense ocean.

However, if washed ashore, the chances of retrieval are increased tenfold. Disappointment soon turned into excitement, when it seemed that we could actually retrieve the two tags. If found back, I could access the raw data on the tag, revealing all the measurements of water depth, water temperature, light levels, magnetic levels and acceleration for every 30 seconds! Far more than what is normally transmitted through the satellite system, which is only a condensed version of the data, this will be highly beneficial to our study on the movement ecology of reef manta rays along the Mozambican coastline. And not only will we be getting this high-resolution data, we will also be able to redeploy these two tags, saving us thousands of dollars.

Path Sat Tag 128924The track of the second tag after it had popped-off. It started about 30km north of Bazaruto Island, and got blown towards Bazaruto Islands by some fierce northerly winds over the course of four days.

The tags were found to be transmitting and floating offshore off Bazaruto Island, and within a few days they seemed to have been washed ashore on the island. Lodges on the island were contacted and flyers, with information on the tags and the reward for returning them, were passed out at the local villages. We quickly got word that the tags were found, and after some phone calls, I set out to meet with the lucky beachcombers in Vilankulos.

Tags Downloading_IMG_4178After picking up the tags, the download of the data could commence


Looking at the data, already some interesting and very different behavior between the two animals can be observed. Tag 128922 showed data of the animal diving down to a maximum of 116 meters deep, but spending his time at an average depth of 17 meters. Tag 128924 however not only dived deeper, up to 184 meters, but also displayed a much deeper average depth of 43 meters. With these deeper depths came also colder temperatures, as low as 15 degrees Celsius. Each animal however also spent time near the surface on a daily basis, showing that they are quite the vertical swimmers.

Another incredibly interesting aspect these highly sophisticated tags record is accelerometer data. Every 1.28 seconds it record the accelerations in G per second across the x, y and z axes.  This will give us insight into how fast these animals can move, and possibly also when they display different types of swimming behaviors. It may additionally show us when they are feeding, cleaning, resting or simply on the move, information that we could previously not obtain.

 The task that lies before us now is to analyze all this data. Obtaining the most probable tracks of the animals, performing dive behavior analysis and acceleration data analysis involved a lot statistical modeling. Not an easy task, but Fabrice Jaine, our data analysis guru, and I will be cracking away at it for the next few weeks, fueling our desire to know more about these enigmatic animals.

Data_IMG_4182The large amounts of data coming from these tags will help us elucidate the movements of these large rays


But why have these two tags shed prematurely? Why did they not stay on the animals until the 10th of October? These questions we can also answer, or at least speculate. The first tag to pop-off, was actually initiated by the tag itself. The animal behaved so consistently for about a week that it set off the Constant-Depth-Release. A built-in feature, this enables the tag to release earlier than programmed if for example the animals has died and is lying on the seabed. Judging by the dive profile of the animal this definitely did not happen, but it was diving so consistent that the average depth was similar every day, tricking the tag into popping off.

 The second tag seemed to have been bitten off by something. This is not something uncommon with tags, as they do resemble small fish swimming with the manta ray. Predators such as game fish or sharks can mistake the tag for a fish, have a go at it, and break off the tether.

 In short, the data we get from these tags is invaluable in the conservation of reef manta rays in southeastern Africa. This is an incredibly lucky start, and let’s hope the other three tags will be retrieved as well! Many thanks to all the people involved in getting the tags back to us; Janneman Conradie of MMF and Big Blue Vilankulos, Luis, Tony, Antonio and Mapanzulo of Pestana Bazaruto Lodge, Anel of Indigo Bay Resort, and Thomas and Arnaldo for finding the tags, Muito Obrigado!

* Written by Daniel van Duinkerken. This post was originally posted on