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Meeting the Mighty

Our boat zigzagged between submerged coral outcrops and passed through a small gap in the fringing reef, writes Nicolette Scourse. We were now in ocean blue - in a great warm current running down the coast of Western Australia. Its heat creates food for the minute and the mighty. They come from the ends of the ocean for the feast.

 

It seemed to be a vast empty sea... but they were there, seen by a tiny spotter plane high above. Our boat slowly changed direction. We took up our appointed places ready to slither through that ambiguous reflecting surface into their world. We had been well schooled using toy models, showing viewing positions (no swimming ahead of its pectoral front fins), distances (3 m. from its body) and code of conduct including no duck diving towards the animals. This was to be a very organised encounter - commendably and necessarily so for animals’ protection. Such rigorous controls and limited numbers of tour operators ensure that future generations will be able see these giant rarities. Sadly elsewhere in the world they are captured for aquarium sensations, or in the wild, are frequently driven away from traditional feeding grounds by intrusion from uncontrolled tourism.

We all stood ready, aiming to be two groups of five each side. Our slight little guide was down into the water, mermaid-like. A Gemini back-up craft to rescue any exhausted swimmers was lowered. We saw nothing beyond dark ripples of undulating light. The guide raised her arm and we were in. Out of range of the bright blue sky, we peered down through a dull cloudy murk. It was like a thick soup needing a bit longer in the blender... and a rich soup it was if one had microscopic eyes -  floating bacteria, single-celled plants and animals, small eggs, and free swimmers such as krill, jellyfish, larvae of Christmas Island Crabs, scallops, squid and juvenile fish. How far ahead should I focus? At what level? 

A vague grey shape gradually materialised around a whitish shallow ellipse of a mouth which was barely open, followed by a chequerboard of pale lines framing solid pale circles - a Whale Shark’s body. The biggest fish in the ocean glided slowly, with no apparent muscle movement. Its wide flattened front pectoral fins were reminiscent of the wings of an aircraft, but instead of a jetstream trailing fish were cadging a lift.  

It moved towards us and we could see its tiny eye: not dark or bright or swiveling in the usual fishy way of inspecting humans, nor the scrutinising eye of reef squid, or the knowing dark gaze of a curious dolphin. It was more of a sleepy eye, preoccupied and unconcerned by our presence – reassuring as this animal was 8 m long (nearly the length of a double-decker bus). Its five classic shark gill slits moved visibly. We started to swim, finning steadily. The gunmetal grey skin was leathery, rough textured like other sharks, in contrast to the translucent shine of fish scales. The ridges and markings of its great body gave it the appearance of an armour-plated submarine, Captain Nemo’s Nautilus image from “Twenty Thousand Leagues Under the Sea” made real. It seemed to glide by magic with efficiency more refined than an Olympic athlete. Meanwhile we were now working our legs hard, finning with our utmost effort feeling water resistance pressing against arching fin blades, breathing hard and tiring fast.  Beside us the retinue of slim silver fish idled along in the slipstream. It seemed like minutes, or was it seconds… who can tell?   

We inevitably slipped back to tail level. Its massive length and the height of its fin made us gasp. The visible potential power of this exaggerated upper lobe and the extraordinary length of muscular body left us in no doubt of the 1 meter = 1 ton ratio. No reminder needed to stay four meters clear of the tail. The very top of this animal’s tail was missing and rough edged, possibly damaged by a boat’s propeller. As we looked, it moved slightly. Shafts of sunlight from the world above caught the edges of front fins and tail and touched them with gold, caught for a moment in a moving spotlight. The bright edges blurred as the giant began to descend, its head out of sight, its aircraft fins merging into a haze. 

In slow motion the massive rear body and tail blended into shadows and dark blue emptiness. 30 meters down there was a Whale Shark below us - and we were treading water in a void.

Their range is wide and deep: it is known they can dive to 700 m (nearly 3000ft). It seems Whale Sharks from the Seychelles fit into the jigsaw, while others have circumnavigated the globe in between visits.  After feeding, some are migrating from these protected Australian waters to further north, where in some areas they unfortunately remain a focus of unsustainable commercial fishing. Their enormous size also leads them to easy misinterpretation as evil threatening monsters to be killed, or as a sensational addition to an aquarium. Female Whale Sharks seem to congregate in seas around Taiwan: the largest, killed in 1996 had 300 young inside her, some still alive, about 40-60 cm long (16-20 inches) and emerging from their eggs – a salutary number  considering only 320 individuals had ever been sighted anywhere until the 1990’s – population numbers remain unknown. Their ovoviviparous habit of retaining eggs within the body and giving birth to live young occurs in many sharks.    Their mating and associated behaviours are still a mystery. The animals we had seen were juvenile males, the norm in this migration to the Australian coast.  It is thought they become mature at about 30 and live to about 70 years old.  

Our four animals had been moving through the water relatively slowly (although not from our swimming viewpoint), filtering plankton – passively floating bacteria, tiny algae, single celled organisms, small eggs, and free swimming creatures as small as 1 mm (0.04ins), including krill, larvae of many types: Christmas Island Crabs, scallops, small jellyfish, squid and tiny vertebrates such as juvenile fish. We had seen their mouths slightly open, but they can open them to more than a meter to optimise feeding. Swimming forwards, water is pushed into the mouth passively – “ram filtration” as in Basking Sharks. Going one better than these distant relatives, Whale Sharks can also feed actively by suction, creating a flow by opening and shutting their mouths sucking in water and then expelling it out through the gills. In 2011, off the coast of Mexico, a diving photographer was apparently nearly sucked in inadvertently along with the flow, but at alarmingly close range he managed to avoid a Jonah style experience, caught dramatically on camera. Photography has also captured new knowledge of their feeding behaviour – they actively target concentrations of plankton or fish, switching feeding method accordingly. A BBC film recorded a Whale Shark homing in on a school of small fish as well as a timed arrival to coincide with mass spawning of fish shoals and the resultant bounty of sperm and eggs. Although of a very ancient and primitive lineage, their food filtering method is highly efficient. The food laden water flows across unique filter pads - sieve-like structures - which separate food from water. Any clogging build-up of food is thought to be cleared by Whale Shark “coughing” which has been observed.   Denser morsels of food are passed on to the back of the throat.

Their regular arrival to feed in these waters between April and July is beautifully timed. The warm Leeuwin current has been flowing south since March and mass coral spawning also occurred in March or April, timed for minimal tide movement about a week after the full moon. By April the water temperature has risen to around 27 degrees C and the massive synchronised spawning has created a rich planktonic soup with its enormous diversity of microscopic life, eating and being eaten. For humans this rich food source is so thick it makes underwater visibility poor; for the sharks it is the realisation of their goal. 

 

Nicolette has just written and illustrated 'Wild Encounters - Try Not To Smile' (on Amazon and iTunes).

 

http://www.wildencountersthebook.com/