Along a small stretch of uninhabitable coastline off the coast of Djibouti lies one of Nature’s treasures which, up until now, few have been privileged to witness. During the months of October to February, large aggregations of young whale sharks visit the Gulf of Tadjoura to feed on the plankton-rich waters within the Gulf of Aden. Although Djibouti is most definitely a no-frills destination that most governments advise against visiting, I can’t resist the lure of these gentle giants.

I have joined a team of researchers and volunteers from non-profit groups Megaptera and the Marine Conservation Society Seychelles (MCSS). We are heading off for five days to build on the existing research data on the large aggregation of whale sharks that are attracted to this region. Sailing alongside the deserted coastline you gradually forget fears of threats such as piracy, and you give in to being unreachable, with no mobile reception. By the time we arrive at Acacia Bay, I find myself finally relaxing and enjoying the adventure. The skiff boats are lowered into the water and we prepare ourselves for a couple of hours of whale shark research.

The waters of Acacia Bay bloom with plankton

The Search Begins

Sitting in the skiff and moving at a snail’s pace just five metres from the shoreline, our research team sits in anticipation, surveying the surface for sharks. Suddenly one of the team members shouts and points and everyone grabs their cameras and enters the water. Timing your entry to meet a fast-moving shark is not easy, especially during your very first encounter. Invariably, I found myself waiting for the bubbles to clear in front of my mask only to find that the shark had raced past me.

Finning after the shark, I watch the team taking their photos for spot pattern identification. Using waterproof military-grade laser sights mounted on either sides of a camera, the team’s images can be used to determine the length of the shark, as well as the sex. Eventually, I give up trying to keep up and instead tread water to get my breath back.

As the cooler months arrive in Djibouti, so do young whale sharks measuring three to six metres in length, although sharks up to eight metres have been sighted. Little is known about where the sharks come from. Local reports from ecotourism operators suggest that these sharks move around a small area of coastline in search of food.

By late morning as the sun climbs higher in the sky, plankton is attracted to the surface. As the wind picks up, currents upwell creating plankton hotspots up and down the coast. Plankton is made up of small or microscopic organisms such as fish eggs, tiny fish fry, crustaceans, algae and protozoans. Whale sharks are filter feeders that swim through the water with their mouths wide open to feed. As they gulp at the incoming water they use their gill-rakers to filter out the microscopic plankton before exhausting the filtered water over their gills for oxygen transfer.

No one can yet say how many sharks are coming to Djibouti, but researchers from Megaptera and the Marine Conservation Society Seychelles are slowly piecing it together

Heads Up

Once the cruising sharks track down these blooms of plankton, their swimming patterns will change to either “ram feeding” or “vertical feeding”. Ram feeding sharks will swim very fast through the water with their mouths wide open trying to filter as much water as possible. As plankton density increases, the sharks will often start to gulp, which will invariably slow their swimming speed. Interestingly, if left undisturbed, a gulping whale shark will often stop swimming and instead rotate itself into an almost vertical position where it will continuously gulp, stationary in one area until the food source is depleted.

I find that it is far easier to find the sharks from the water, and so, as the boat comes to collect me, I instead wave them on, and ask them to come back for me in a while. Watching the boat further down the shoreline now, I keep an eye on the team jumping in on another shark 40 metres away. I know I now have a 50/50 chance of the shark coming my way. It’s not long before I spot the tip of the shark’s tail breaking through the water’s surface, sweeping quickly from side to side.

Dipping my head underwater, I come face-to-face with this majestic fish and fire off several shots. I swim alongside the giant for some time, giving me all the opportunities I need to get the photograph I want. As I follow the shark I notice that the density of the plankton cloud thickens, and as it does, the behaviour of the shark changes too.

Using “ram” and “vertical” feeding techniques, the animals move slowly from plankton cloud to plankton cloud

Slowing its pace, the whale shark opens it mouth and starts to repeatedly gulp at the cloud of plankton. In almost a trance-like state the shark stops swimming and instead manoeuvres itself so it can feed vertically in one spot. As I get perhaps too close to this feeding shark, I am reminded that this giant is fully aware of my presence. As it moves away from the cloud of food I realise that I have disturbed it.

With experience from my previous visits I have learnt not to chase the sharks and instead to stay with the food, and as I follow the cloud of plankton, it’s not long before other whale sharks join me to feed on the soup of microscopic organisms. It’s a great reminder that understanding an animal’s behaviour can pay off with fantastic encounters.

For the rest of this article (Scuba Diver 2013 Issue 3 No 74) and other stories, check out our past issues here or download a digital copy here.

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