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Swimming with Whale Sharks in Tanzania

News item submitted by Frontier
News item dated 10 Dec 2009

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I glance above the water and 20m away a monumental fin towers upwards, standing 1m proud of the water, what seems like an unbelievable distance behind it a huge tail breaks the surface, lazily sweeping from side to side. It is heading straight for me, but when I look under the surface, the deep blue water rich with plankton hides all but the shards of sunlight piercing into the depths. I try and peer into the blue, but it must be too far away, the anticipation is unbearable. Every breath from my snorkel seems ear shatteringly loud, the languid water perfectly still, out of breath from the fast swim from the boat, adrenalin surging. I glance out of the water again, so close, maybe 10m away the fin seems impossibly large, still cruising straight towards me, and the tail set a good 5m back from the fin. I put my head back underwater, it’s here!  

Until you have seen one, there is little to prepare you for the scale of the world’s biggest fish, Rhincodon typus, commonly known as the whale shark. To say that a fish measuring up to 12.65 meters and weighing in at more than 21.5 tones is big seems an understatement in the extreme. The shark is found in tropical and warm oceans, living most of its 70 year lifespan in the open sea, only seeking shallower waters during seasonal feeding aggregations. This gentle giant is a filter feeder, similar to the UK’s own huge shark, the basking shark, feeding on macro-algae, plankton, krill and small nektonic life such as small squid or vertebrates. Like the basking shark. This species, despite its immense size, does not pose significant danger to humans, countering the popular misconception of sharks as "man-eaters". Due to their magnificent size and strange technique of using their entire body to glide through the water, contributing to an average speed of only around 5kmh, whale sharks are not much faster than a swimmer in the water. They are gentle, graceful and inquisitive animals, and provided you watch out for the powerful sweeping tail, snorkelling with one of these majestic fish presents one of the pinnacles of wildlife encounters. During the months of December to February, whale sharks gather in the warm nutrient rich waters off western Mafia Island, and if you are lucky you may chance across a group.

My vision is full of the biggest fish I have ever seen, the head looks like the front of a small car, wide mouth open, steadily gathering microscopic food. Transfixed to the spot, the shark casually so gracefully rolls slightly and passes by close enough to see the beautiful white spotted skin, reflecting back waves of light from the surface. A surge of small pilot fish ride in front of the mouth like dolphins playing at the bow of a tanker, huge remora, suckered on to the sharks belly get a free ride over the oceans. Tiny eyes look back bemused and curious to the funny humans following close alongside. Slowly cruising through the water, we find it easy to keep up, the massive body flexing from side to side. 

Wary of the 2m tall tail fin and the massive power, we keep a respectful distance, but the shark is curious, rolling round it comes back through the middle of our group, snorkellers dart in each direction eager to get out of the way of the boat sized fish. We need not have worried, with an agility that belies its bulk the shark flicks between us with ease. With a flick of the tail it is over, once more the shark disappears into the blue. But no sooner than we lift our heads out of the water, another shark cruises into our group, again curious of our presence. After 30 minutes, and with big smiles and aching legs we claw back onto the boat, everyone is grinning and there is a sense of the surreal running through the boat, we have just snorkelled with four whale sharks, the biggest fish in the sea, simply incredible!

Trevor Worsey

Find out more about the Tanzania Marine project here.