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Shacks 2012

Created By: Roland Ortega
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http://www.okavango-croc.com/ 

Croc Cam!

Following one of the most mysterious animals on earth while it travels its underwater world - this is something I have always dreamed of doing. Many film makers and scientists have tried this in the past, with not too much luck unfortunately. With such an incredible improvement in camera technology and the fact that the Okavango water is so clear in the winter months, we were able to successfully film a Nile crocodile underwater, using a small high definition camera attached to the crocodiles nuchal shield (hard bony plate on the neck of the crocodile). This particular sequence was used in our recently produced film "Croc Labyrinth" Produced by Earth-Touch for National Geographic. Although we have up to now, spent a huge amount of time with crocodiles underwater, I always ask myself how our teams presence has affected the behaviour of the crocodile underwater. We know that the crocodiles are aware of us underwater and this will almost definitely affect how it positions itself and moves. The idea of a remote camera, is to actually give the crocodile some time to recover from the capture and then to hopefully start behaving in more of a natural way, so that we can start to understand its natural behaviour underwater.

One of the first and most pressing questions I had was, are these crocodiles actively using the underwater cave systems to recover from stress? {1}The specific stress that we were evaluating would be our capture and release of the animal, but other stress factors exist in the wild for these crocodiles, such as predation or attack from larger crocodiles and people using the river. What the underwater floating papyrus system provides for crocodiles are slightly warmer water, less current and low light for hiding. While exploring these underwater cave systems, we also noted some very clear holes in the papyrus which provide sharp beams of light in this very dark environment (we actually use these light beams as markers for navigation in these caves). It occurred to me that these holes may also provide the crocs with an opportunity to breath whilst hiding in this cave environment. In order to capture this behaviour, we would need to give the crocodile enough time to recover from the stress, which would then allow it back up to the surface to take a breath. A remote camera would be the only way to see this!

I have added some frame grabs from our footage to show you the sequence of events as they occurred (and are shown in the film). Firstly we had to attach the camera in a way that it would be secure and accurately frame both the surrounding environment and the crocodiles head - with a bit of luck and some accurate free hand aiming - we managed to do this. The croc was then released off the front of the boat.



The croc immediately moved to the bottom of the river channel, which it travelled along for a short distance. {2}As we have seen in all our dives, the croc prefers to move along the river floor and on most occasions will slowly walk along the floor rather than actively swim with its legs tucked to the side of the body. In this case the croc was moving downstream, so really there was no need to move any faster than the current was going. The croc then moved to the side of the channel where it began to hug the side walll very closely. It was almost as if the croc was using its head to sense all objects on the river floor.




The framing on these shots were perfect! You can clearly see the crocs head with bony protrusions, eye sockets and the tip of the snout. If you look carefully to the side of the eye socket, you can actually see the pupil of the crocs eye (left eye). When watching the footage, you can see how the croc is relying on fine tuned senses around the snout to aim the snout in the direction in which it should travel. Traveling forwards with eyes that are placed on either side of the head (rather than facing forward like humans), will have its own set of challenges of course.




Because this would be the first time anything like this has been done, we opted to retrieve our camera sooner rather than later - unfortunately for us, after watching the footage, we realised that we had not given the crocodile enough time to settle down (thus showing us the behaviour we needed to see). We were lucky enough however, to get our camera back and at least see that this technique was effective in filming behaviour underwater! Excellent news!! Now our team needed to replicate this method on another crocodile, but this time, give the crocodile enough time to settle down and hopefully prove that these floating papyrus mats are being used as a resting sanctuary during periods of stress.

What can be seen with our second attempt, is the croc moving into a darker portion of the river - before eventually swimming into a dark cave of floating papyrus. Of course at this point the low light levels left us with completely black images with just some sound of the camera hitting against vegetation. The camera had also been knocked around at this stage, changing the angle of the frame, but lucky enough throughout all this footage we could always see a portion of the crocs head.





Because we were familiar with this area underwater, we could now see that the crocodile made use of the first bit of floating papyrus that it encountered after being released. It was a deliberate move by the crocodiles to get out of the bright main channel and into a darker portion of the river. Our crew watched (or listened) to the rest of the footage as the croc moved in this pitch black environment, would our croc return the light or even better, find one of the breathing holes we had seen while under the papyrus? Eventually the croc moved. In the distance we could see light! {3}The croc had now moved into a position we always suspected they used underwater. Sitting in the dark, facing the light of the main channel. This way the crocodile cannot be seen from the main channel, but has optimised its own position to see outwards (for any potential threat). This was great!




We had already achieved so much with this experiment and were able to now accurately look at the crocodiles underwater bahaviour. This was truly a look into the crocodiles own world - no divers - just the crocodile. With this crocodile, we gave the animal a lot more time to relax and show us some more of its natural behaviour. {4}When a crocodile is stressed underwater, it has the ability to hold its breath for many hours. While this is not ideal for the crocodile, it is an adaption that it has made to deal with threats above and below the water. So one sign that a crocodile is beginning to relax, would be a crocodile moving back up to the surface to take a breath. By doing this the croc is showing that while it is not fully relaxed, it feels safe enough to return to the surface for a breath. What we saw next totally blew us away!! After spending some time under this mat of floating papyrus looking outward, the crocodile began to slowly swim back up to one of the "holes" in the papyrus! The croc knew exactly where it was going and why. The camera captured the crocs head swimming upwards toward the surface and before popping out, the croc expelled a large burst of air from its nostrils.




Although quite rough and over exposed, this sequence of footage was able to show the crocodile making use of a "breathing hole" in the papyrus to take a breath of air, before returning down to the bottom of the cave again - excellent results! This is exactly what we suspected these crocodiles were doing. This habitat thus provides crocodiles with a very effective sanctuary for escaping predatory threats. In the image below, the camera captures the exact moment when the crocs head pops out of the water for a big breath. You can see by the surrounding vegetation that this is clearly a well covered section of open water which provides the croc with a certain amount of protection.




After taking a large breath for not more than 2 or 3 seconds, the crocodile returned to river bed again. So what we have seen is not complete relaxation by the croc, but enough to allow the croc to return to the surface to avoid building up an oxygen debt under water. This was an incredible result for our team! We have basically shown what an essential habitat the floating papyrus fringing the main channel, provides for crocodiles. Under these floating mats of vegetation, the crocodile is able to hide, warm up, safely breathe air and even potentially bask (by exiting the water through these breathing holes and basking on the floating papyrus). Papyrus is a dominant vegetation type fringing the main river channel in the Okavango and massive stands of this plant are found throughout the Okavango. In the Panhandle, severe burning of the papyrus takes place every year during the breeding season of crocodiles (July - Sep). Now that we have shown how important this habitat is to crocodiles, we can now assess how harmful these fires can be to the crocodile breeding process. During breeding, many large male crocodiles will congregate on the main channel and continue to fight with other smaller males in their territory. During this time, smaller male crocodiles will rely on habitats which can protect them from predation from other crocodiles. If this papyrus habitat is burnt, these caves may become filled with dead vegetation and breathing holes may become covered. Burning will thus continue to be a big threat to the breeding and nesting behaviour of Nile crocodiles in the Okavango Panhandle.




Thanks to our very successful croc cam experiment, we are now able to confidently say that crocodiles make use of this extensive habitat type and we need to do everything in our power to conserve this habitat !
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