Jonathan travels to Holbox, Mexico in search of the massive whale shark—the world's largest fish. Reaching 50 feet long, these animals grow larger than a school bus, but they are completely harmless since they eat only plankton and small fish. Jonathan gets up close and personal to a mouth the size of a small car in his investigation to discover why so many whale sharks visit Holbox every summer.

#underwater #scuba #scubadiving #sharks #whalesharks #holbox #mexico

This is an HD upload of a previously posted Season 2 segment.

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Holbox is not your typical tourist destination. Until recently, this sleepy island wasn’t much more than a fishing village.

There are no paved roads, and everyone gets around in golf carts or other nonconventional transportation. There are almost no cars on the island.

The highway here is a stretch of beach where you can hit maybe 20 MPH if you have a fast cart. Downtown, this island has the charm of a place not yet discovered by throngs of tourists.

But everywhere there are signs. Something special has been discovered here. Offshore in the cool waters of the Gulf of Mexico, a giant lurks!

To find the whale sharks, I get up early to meet the boats to take me and the other intrepid snorkelers on the adventure of a lifetime.

These are converted fishing boats. Instead of depleting the ocean of fish, these fishermen are instead making their living taking tourists to swim with the fish. A really big fish.

Using a GPS device to help him find the shark hot spot, the captain takes us about an hour offshore.

Our guide Andreas stands in the bow, with a carefully trained eye on the horizon.

Soon, we pass a pod of dolphins.

We also see manta rays, and large schools of fish feeding in a frenzy.

Soon, he spots what we are looking for—the large fin of a whale shark sticking up out of the water.

As we pull the boat up alongside the shark, I can see its massive mouth open and funneling water in, like a gigantic storm drain. The shark is feeding. But what could it be eating? It’s more than 30 feet long. What could feed such an enormous animal?

To find out, I don my snorkel gear and hop over the side.

The whale shark passes right in front of me. The water is not very clear, and this is where I get my first clue what is going on here.

The sharks have come to this section of the ocean because it is filled with plankton! Whale sharks might be the biggest fish in the sea, but they eat only plankton and small fish.

The word plankton comes from a Greek word meaning drifter, so plankton are drifting organisms.

Early in the morning, when the water is calm, the plankton forms a thick layer near the surface.

He's just surface feeding. What the whale sharks do here is they swim across the surface of the water with their mouths open wide and all that plankton that's sitting right there at the surface gets funneled right into their mouths.

The enormous mouth swallows up huge quantities of water.

The water comes back out through the shark’s gills, but comblike structures in the gills capture the plankton like an enormous spaghetti strainer. So the whale shark swimming through the water is like a big pool skimmer, filtering the plankton for breakfast. Each shark eats hundreds of pounds of food every hour! It turns out that eating plankton is very efficient for a large animal.

Conditions here around Holbox Island are perfect for plankton in the summer. The water is not as clear as other islands in the area, but these conditions attract a vast number of whale sharks, manta rays and fish—all animals that eat plankton.

The fish attract other predators like dolphins, birds and bigger fish. That’s why Holbox has always been a great fishing area for the locals.

I can’t believe how many sharks are around the boat. I can count as many as ten at a time. I have been to a lot of places around the world to swim with whale sharks, but never anyplace with this many!

Soon however, as the sun gets higher in the sky and the air gets warmer, wind picks up and waves start to form. The plankton layer dissipates, and the sharks dive down deep, out of sight.