This week’s instalment from marine biologist Robin Aiello sees her come face to face with the awe-inspiring whalesharks in the waters off Halaveli.

Whiptail Ray

It has been another amazing week full of beautiful dives, snorkels, lagoon cruises and island walks. The weather has been clear and warm, and the seas so calm that you can do an entire marine biology session from the surface without even getting wet.
I have, in fact, been spending hours on the jetty with guests looking down into the sea and spotting some fantastic animals. We have many harmless blacktip reef sharks that slowly cruise back and forth under the jetty, whiptail rays that look almost like eagles flying through the water, unicorn fish with their long horns sticking out from their foreheads, long slender coronet fish with their huge extended mouths, and bluefin trevallies (also called jacks) chasing schools of small silver fish.

Bluefin Trevallies

The trevallies (jacks) always put on an exciting show for us as they stalk and hunt the small silver fish that form massive schools in the very shallow water at the beach.

Small groups of 3 – 6 bluefin trevallies swim up and down the beach, getting closer and closer to the shore and forcing the small fish to form tighter and tighter schools – it is like cowboys rounding up the cattle on a range.

Bluefin trevallies

They do this for some time, then, without any warning, there is a huge commotion. The trevallies have decided it is time to strike, and change direction at full speed (which is really really fast) and dash through the school, grabbing fish as they go. The small silver fish, in response, take off in all directions like a firework display. They will even jump out of the water and land on the beach in their sheer panic to get away.

But, there is no where for the small fish to hide. Suddenly other predatory fish join the feeding frenzy, and if that is not bad enough, the seabirds and herons fly in from all directions to join the mayhem and pounce on any fish they can. The whole frenzied activity lasts only a few seconds, but what excitement! Sometimes I feel sorry for the poor little fish!

An unplanned evening snorkel

Probably the most unusual thing that I have seen in a long time was spotted one evening from the jetty. I was heading to dinner, all dressed up, and one of the guests asked me what it was – I had no idea – didn’t even know if it was manmade or natural.

Diamondback squid egg case

So I ran back to my villa and grabbed my snorkeling gear and jumped into the water.

This thing was weird! At first, I had no idea what it was. It was in constant motion, rolling around and undulating, but I soon discovered it was the water movement that caused it to move – it was not actually alive. It was slimy and felt like thick mucous, and to add to the bafflement, there were thousands of little pink/purple balls embedded in it.

Finally it dawned on me that it had to be some sort of egg case – most likely molluscan from either a snail or a squid. After a couple of hours of research I discovered that it was, in fact, the egg case of a very large squid that reaches a size of over 1 metre called the Diamondback Squid. This squid would have laid the egg case out in the lagoon and the tides, currents and waves washed it into the shallows. Very interesting.

Diving with whalesharks

Yesterday, though, was the real highlight of my whole visit – every Sunday the Dive Center offers a day trip to find and snorkel with whalesharks. And what a day we had!

Thanks to our amazing boat crew, and of course the legendary snorkel guide Santana, we had the wonderful experience of swimming with 3 large whalesharks. Amazing! It is no easy feat to find a whaleshark – since they are fish, they do not come to the surface to breath like whales, so the only way to find them is to patrol an area – up and down along the coast. The crew stand lookouts on the roof of the boat looking for a large dark shadow in the water.

Whaleshark

Then, if one is spotted, there is a flurry of activity as we get on our gear and jump overboard. At this point, the race begins. Although these huge animals are barely moving a fin at all, they maintain such a fast speed that we as mere human snorkellers must kick and kick and kick as fast as possible to keep up with them. They do not seem to be bothered by us at all – in fact, on several occasions they appeared to be curious and changed direction to come right up close underneath – within only a few metres of us.
When they are this close, they take your breath away. They really are special creatures!

They are so spectacular, that this creature will be the topic of my Creature Feature for this week.

Creature Feature – Whalesharks

Whalesharks are well known to frequent a spot on the southern part of the Ari Atoll – no one really knows why they ‘hangout’ in this area. But they seem to be mainly young-adult males that are about 6–8 metres in length.

Although this is considered relatively small for a whaleshark (they can reach sizes of over 12m) they are still incredibly impressive. In fact, whalesharks are the largest fish in the world.

Whaleshark

Whalesharks are a type of shark – not a whale. They, like all sharks, have a cartilaginous skeleton rather than bone, have what are called denticles covering their skin instead of scales, do not have an air bladder, but use a liver full of oil for buoyancy, and of course they have ‘replaceable’ teeth rather than only one set like most reef fish. Sharks have hundreds of teeth and can go through as many as 30,000 teeth during their lifetime.

What happens is that teeth that form the ‘front-row’ periodically fall out, and within only a few days another tooth that behind in the ‘second-row’ will rotate into position. It is kind of like a conveyor belt of teeth. In this manner the shark always has fresh, sharp teeth! Whalesharks, although they do not use them, actually have about 300 very small teeth.

How whalesharks feed

So how does a whaleshark feed if it does not use teeth? Well, these giants of the sea, feed on some of the smallest animals in the ocean, plankton, by a method called filtering feeding.

Inside their mouths they have an unique system of filter-pads that trap all the small plankton – a lot like a sieve.

Whalesharks feed in two ways – ‘gulping’ and ‘ram feeding’. If there is plenty of concentrated plankton in the water, these sharks will stay in one place and take in huge gulps of water full of plankton.
If, however, the plankton is spread out in the water, then the sharks will swim at an average of 4km per hour with their mouths open – when they have enough food, they will swallow, then resume feeding – this is ‘ram-feeding’.

To watch them feed is incredible. They have huge mouths – up to 1.5 metres wide and they can filter over 300,000 litres of seawater per hour.

Identifying whalesharks by their spots

Other than the sheer immense size of these fish, the other really noticeable feature is the patterning. They are fully covered with spots and dots, and some lines – really beautiful.

They almost look like a bright starry night sky. In fact, a few years ago a couple of scientists came up with the interesting idea to use a computer program designed for tracking stars to document the spots on individual whalesharks.

Since the patterning on each whaleshark is unique for that individual (much like our human fingerprints are unique to each person), scientists have been able to compile a global database of whalesharks from photographs of their spots.

So, when you visit Halaveli Resort, be sure to take the trip out looking for whalesharks – it is fantastic!

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