What Is The Biggest Fish Of The World Ever Seen?

  At up to 40 feet long and weighing several tons, they are one of the most spectacular sights in the sea. There are 28,000 species of fish. About 400 of them we call sharks, and the largest of those is the whale shark or Rhincodon typus– it’s the largest of all fish.

 An average whale shark is twice the size of the largest great white shark. So you’re really talking about an animal that is a leap and bound bigger than its next biggest relative. Whale sharks are found everywhere in the tropical oceans. 

So, you find them in the Pacific Ocean,the Indian Ocean, and the Atlantic Ocean. Anywhere where it’s warm enough, which pretty much means anywhere where it’s over about 72 degrees Fahrenheit.


Food Consume By Whale Sharks

 While they may be the largest fish in the sea, the animals are gentle giants.These are sharks that feed by filtering tiny food items out of the ocean, rather than having huge teeth and biting things. 

They’re a very large animal that’s feeding very low on the food web. It’s pretty much the same way that great whales feed.

They’re fairly indifferent to the presence of people, and they really present no harm to us at all. It’s amazing to be in the water with an animal three or four times your size -watching the majestic movement, the power. And at the same time they are so tame, so gentle, so fearless, it’s a fantastic thing. 

Vast Migrations


Named for their size and feeding habits, the animals are capable of making vast migrations. Yet, despite their enormous size, little is known about whale sharks. We don’t really know what role they’re filling in the ecosystem. 

Gathering Of Whale Sharks


So, we’re asking simple questions like how many whale sharks are there and where do they come from, and where do they go. 

Whale sharks are thought to be solitary animals most of the year, but during certain seasons they gather in large numbers in different places around the globe, including off the Yucatan Peninsula in Mexico.

 This is the largest aggregation of whale sharks in the world, and it’s happening a stone’s throw from one of the biggest tourist destinations in the Caribbean.


It really is one of nature’s wonders. Major funding for this program was provided by The Batchelor Foundation, encouraging people to preserve and protect America’s underwater resources.

Tourist Destination

 And by Divers Direct Emocean Club, inspiring the pursuit of tropical adventures and scuba diving. Cancun, Mexico, is one of the most popular tourist destinations in the Caribbean, attracting millions of visitors each year.


But just offshore from the miles of hotels and hustle and bustle lies a fragile yet highly productive ocean ecosystem. Each summer, the region is home to the largest known aggregation of whale sharks in the world. About twenty years ago, we thought that whale sharks were solitary off-shore animals.

 And then they started to discover that in certain places in the world, there are places quite close to the shore, where whale sharks actually gather in large numbers. We discovered that one of those places is Yucatan Mexico. And in two places at least here in Yucatan, Mexico, near Isla Holbox, and here near Isla Contoy,there are places where dozens, sometimes hundreds of whale sharks gather in the same place.

But Why Whale Sharks Gather Here?

The reason whale sharks come here is to feed. And when they come to Isla Holbox on the Northern side of the Yucatan, they mostly come to feed on zooplankton. But when they come to the Caribbean side of the Yucatan, they’re here to feed on fish eggs. 

And they feed on fish eggs, and nothing but fish eggs, all day, every day for at least 4 months. It’s the most amazing biological aggregation I’ve ever seen.They tend to be sub-adults, so these are not fully grown whale sharks. 

They are in the high twenties to low thirties, feet. And they tend to be overwhelmingly male, which is interesting,because if you go to the offshore locations where the really big animals are, most of those animals are female.

 So there seems to be some sort of segregation in the ocean,where juveniles and males go to one place, and adults and females go to a different place.We don’t really know why this is. While the animals can dive to at least a mile deep, they tend to feed at or near the surface. 

We’re pretty sure that whale sharks fall into that feast or famine feeding mode where, when you know when conditions are good as they are here in Mexico, they can eat nonstop for four months. But then when they leave they can go a really long time before they have the need to eat again.And that’s how their life goes. 


They go from buffet to buffet, but they’ve got to run a marathon in between. Watching dozens of whale sharks vacuuming up plankton is a spectacular sight. You sail into this ocean of fins. It’s quite extraordinary to see the size, and it never gets old. It’s like being a kid. You’re just very excited about seeing these animals.

This aggregation first caught the attention of scientists in 2003, when locals started taking tourists to see the animals. The tourist operations started when fisheries deplete, and we figure out that there was so few knowledge about the whale sharks.

 Our research was developed in order to gather enough information to manage the tour operation.The Mexican National Commission for Protected Areas formed Project Domino with U.S. collaborators to better understand the animals’ movements and devise conservation measures.

To ensure responsible whale shark interactions, local authorities also worked closely with researchers and other stakeholders to develop guidelines for tour operators.There are about nineteen different guidelines. It is mostly to be respectful with the sealife. 

Based on the research findings, the government created a whale shark biosphere reserve in 2009 to protect the animals, but experts quickly discovered that the whale sharks also aggregated outside of the boundaries of the reserve.

That demonstrates that animals do not care about borders.In the meantime, popularity of the tourist whale shark encounters took off…In 2003, there were about ten boats only. By 2004, there were fifty boats allowed. Nowadays we have more than 250. 

Ecotourism(tourist connecting with nature)

Ecotourism is definitely a two-edged sword.It’s a tremendous opportunity for people to connect with nature. And we absolutely want to encourage that. But we’ve got to do it in a way that is going to be safe for the people and safe for the animals. This is no longer ecotourism. It’s massive tourism.


 If you can imagine over a hundred boats at the same time on that small area. All the fumes, the possibility of leaking oils and things like that, could be a disaster. When you have that many boats, and that many animals, all in the same place, it’s pretty much inevitable that at some point, a propeller is going to meet flesh.

 And we see a significant portion of the animals show signs of recent interactions with boats. We lack a lot of enforcement. It’s supposed to be surveillance every single day, but to be honest, in the last three years, we’ve been having the visit of the surveillance people for no longer than three days in the whole season.

 It really falls back on the eco-tour operators themselves, to be self-regulating, and as we know from banking and other sectors of society, if you rely on people to regulate themselves, it doesn’t always go as well as it could.

 Rafael says that while most tour operators are trying to be conscientious, they are facing a tremendous amount of pressure from ticket agencies, which guarantee guests animal encounters or they get their money back.That’s in my opinion, is something that should never be existed at all because that is putting a lot of pressure on the animals. 

Protecting Whale Sharks

The ideal thing should be to establish a max number of boats to interact per day in the area.It really does need a disinterested third party to come in and say, okay, too many boats,we need to limit entry, we need to limit the number of people, we need to increase the costs of doing this because the market forces have made it so cheap that margins are so razor thin, that the whole system is really running on a knife-edge.


To better understand the animals and make conservation recommendations, the Georgia Aquarium has teamed up with Rafael de la Parra and others to form a non-governmental organization.We call that Blue Realm or Ch’ooj Ajauil which means Blue Realm in Mayan. Reino Azul in Spanish.

What we’re trying to do is take a broader approach than just whale sharks and look at protecting the whole marine region because we recognize that the whale sharks are a reflection of a much bigger picture, which is this extraordinarily productive ecosystem that they have here.

Despite the fact that tourists are coming to see the animals in droves, still relatively little is known about these charismatic giants, nicknamed “Dominos” by the locals because of their polka-dotted skin pattern. One way to get a good estimate of how many animals are in the area is to count them from the air.Okie dokie, here we are. 

Locating Whale Sharks In Oceans

Look a bunch of them right here. Lots of them.Woohoo! Many many many, wow! On the aerial survey that we are conducting,hopefully once a week for the whole five months that the season last, trying to locate them,and to count them. So far in 2009, was the largest aggregation ever. 

And we counted upto 420 whale sharks in a single spot. Today, we count up to 170.Little one. Another way to study the animals and track their movements is to satellite tag them. A lot of what we’re doing here involves deploying different types of tags that will tell us about what whale sharks are doing when nobody’s watching. We have what we call archival tags.

Attaching Tags on Whale Shark



Those are tags that record data about what the whale shark is doing. They save it inside the tag,and then at some predetermined time the tag is programmed to release itself from the whale shark, float to the surface, and begin to report its treasure trove of data via satellite back to the researcher.

 We also have real time tags. Those focus on telling you where the animal is right now. And those are tags that are towed along behind the animal, floating at the surface. And they report to us via the same GPS system that your car uses. And so those are able to tell us, at any given moment, where the whale sharks are going. 



One of the things that I’m really excited about this year is that I’m connecting those realtime tags to social media. So this year our whale sharks are going to be tweeting their locations in real time by Twitter. And that’s a really fun piece of science that’s going to allow kids and the public to follow along with science as it happens.

In addition to recording the animals’ location, the tags also collect temperature data and depth profiles. Attaching tags of any kind to whale sharks is the biggest challenge. We struggle with getting them to stay on.Whale sharks are very fast and very large. They have the thickest skin in the animal kingdom. So getting a tag into their skin and getting it to stay there for months turns out to be much harder than you think.

 Through the use of satellite tags, experts have been able to figure out a general migration pattern for the animals.There are other places in the Caribbean where you can see whale sharks all year, in Honduras for example, around Utila. Other places like Belize, you see them mostly in the springtime,and then in the Gulf of Mexico, mostly in the summertime and into the Fall. 

And this reflects a rough migration pattern where they migrate up the coast of Mesoamerica, and then into the Gulf of Mexico, where they do a big loop over the course of the summertime.But as with anything, there are always exceptions to the rule…There’s a famous whale shark called Rio Lady who was tagged by Bob Hueter from Mote Marine Laboratory. And Rio Lady was tagged here at the offshore location, and she went off to the south Atlantic. 


She didn’t go into the Gulf of Mexico at all. In fact she went the exact opposite direction. She went right across the Caribbean and out into the islands in the south Atlantic. Her tag came off, not far from a place called St. Peter and St. Paul Rocks.

 Which is right on the equator, about eight hundred miles off the coast of Brazil. And so her total migration path was over four thousand miles. Since then,Rio Lady has returned to the aggregation site in Mexico, where scientists were able to puta new tag on her. So we’ll see if she goes back to that offshore location. Why does she go there? Why does she do something different from all the others?

We think she’s a big pregnant female. And we suspect that she probably was going to that offshore location for pupping or some other part of the reproductive cycle.Reproduction is probably the biggest black hole in our knowledge about whale sharks.Nobody’s ever seen them mating, nobody’s ever seen them giving birth.People have found occasionally newborn whale sharks in the size of sort of one to two feet in length. 

And we do know that they give birth to live offspring. And that females can have as many as three hundred babies in their uterus at once.During whale shark season, Rafael and his wife spend three or four days a week studying the whale sharks from the air or in the water. In addition to tagging the animals, scientists also take photos to identify and track the whale sharks.

You have to jump and chase the animal, and be perfectly perpendicular, and take the photograph right behind the fifth gill, on top of the pectoral, and catching as much as possible, the dorsal part of the animal. 

And if you can get that photo, and mark some spots on it, and upload it to this website, there is a computerized algorithm that then compares that photo with every other photograph in the database. And there are whale sharks from all over the world in this data set. 

And it returns a list of potential matches,and then you can you can look at them visually to confirm whether in fact you’re looking at the same animal or not. Using this process we’ve now got over a thousand animals in the whale shark aggregation from our site in Mexico.We have some animals here that now have ten-year visitation histories or more. 

And these animals stopped becoming numbers, and start becoming old friends for us.One big concern the scientists have is boat collisions with the animals.When they are feeding on surface, they are vulnerable to boat collisions, or propeller damage. And in this area, besides the tourist operation, we have a lot of traffic. 

We have at least three to four times a week, a couple times per day, big cargo ships passing right where the whale sharks are aggregating. To avoid potential disaster, the scientists want to collect data on the ship traffic occurring in the area. Vessels over 300 gross tons are required to use what is called the Automatic Identification System.And what the Automatic Identification System is, or AIS, is a method for tracking vessel sat sea.


We are looking for the highest point for miles around so that we can cover as much of the ocean with the AIS as we can.This tower behind me is it. All righty.After a lot of hard work, the lights are blinking. We’ve got power, the solar panels are charging the battery, the antennas are up, everything’s working, which is great.

We’re going to want to at least archive vessel traffic for a year, look at seasonal changes, and things like that. 

We’ll look at the sightings of whale sharks that people have collected over years. And we’ll combine those sightings, and look at where ship traffic intersects with those sightings. And then what we’ll be able to do is dois some statistics to look at the risk of collisions between feeding whale sharks, andships.

 When we see what the risk of collisions is like, we can make recommendations to slightly tweak the shipping lanes around aggregations of whale sharks.And that’s really going to help us work with the maritime industry to say ‘hey,of course you guys have rights to these waters as well. 

But if you could just move your shipping lane a mile to the east, you’re going to reduce the chances of hitting whale sharks by so many percent. That kind of informed decision making I think is the best way to work together. It’s been done with whales, in particularly in the U.S. with the North Atlantic Right whale, where they’ve shifted traffic lanes,just ever so slightly to reduce the risk of collision with these Right whales. And what that’s done is just a few degrees shift in the shipping lane, has resulted in more than fifty percent reduction in risk to collision with Right whales. 


And a more than eighty percent reduction in risk from collision with other large baleen whales.We really get great satisfaction from taking the science and turning it into effective conservation outcomes. In addition to using traditional satellite tags, Jake is also experimenting with a new tag design that he’s putting together himself.He assembles the tag in his hotel room before the team heads out on the water.

What this is doing is recording pitch, roll and heading, as well as depth, so every time the animal changes direction, changes depth and changes its orientation in the water, we’re able to measure that. And this is recording a hundred times a second. It’s sort of like we’re able to ride along with the animal and see what it is doing underwater. 

We need to recover these tags to get the information off them. Because these tags are recording data at such a fine scale, and because it’s – all that data – it’s not possible to transmit over satellite. The scientists put one of these behavioral tags on a shark they nicknamed Senora Elastica. 

For the next three days they hoped to see her again at the aggregation site to recover the tag.We thought she had gone. We thought we had lost her. And then Jake went out to take some photos one day, just really for recreation. And from the deep, underneath him, Senora Elastica rose from the blue, and he was able to reach down and pluck the tag off. 

And now we have a hundred hours in the life of a whale shark, which is, really an extraordinary dataset that nobody’s had before. Once the team returned to the Georgia Aquarium in Atlanta, they began to look at the data in the lab…And it is so much fun, I have to tell you. The way that you can reconstruct her movements in three dimensions, you can see every tail beat, you can see every dive and every feeding behavior. 

And that’s really really exciting.We’ve covered several night times several daytimes, some surface behavior, some bottom behavior. It really is extraordinary detail that we’ve never had before about what whale sharks do. One of the things that it really revealed to us is how much time they spend going up and down. 

We thought a lot of the time they were either at the surface or at the bottom. But as we look at the data in more detail,we see that they’re pretty much constantly going up and down. We really were surprised exactly how much of their time they spend in transit.We’re probably underestimating how many whale sharks there are out there. 


Because we base that on a surface assessment. You look around, you say ‘oh there’s about a hundred and fifty animals here.’ But if there’s an additional thirty to forty percent that are on the bottom at that moment, and they’re going to swap with other animals that are currently at the surface, then you’re probably underestimating exactly how many whale sharks there are in your aggregation. 

That’s probably a good thing. We’d like to know there are more animals out there, but it’s the sort of information that we wouldn’t have had before this kind of tagging technology.So it’s very exciting for us for the first time to be able to see what whale sharks do in their spare time. The Georgia Aquarium is the only facility outside of Asia that has whale sharks on display. We have four animals in the aquarium. Two males and two females.

 They came from Taiwan. So those are Pacific animals, not Atlantic animals. The Aquarium’s research staff not only conducts research in the field, but has also teamed up with Emory University to sequence the genome of whale sharks, using tissue samples collected from captive animals.

We take the DNA and we work in a lab to create what’s called a sequencing library. Which is a sort of form of the DNA that can be sequenced by the instrument. Then what the instrument effectively does is it converts the chemical information to data. And then really the bulk of the work involves putting the data together.

Whale shark has so many like unique features, and the genome size is so big, so if we decipher the genome of this whale shark, then definitely we will be able to know why the whale shark is so big, and why whale shark has some very unique feeding mechanism. 

And how the whale shark is related to other shark species. The other reason the genome is interesting is that sharks were the first group of vertebrates to evolve an adaptive immune system. So they’re the first vertebrates to have specific antibodies in their blood to particular diseases. 

And so if we want to know about where our own immune systems came from, looking in in the tissue and DNA of sharks is a great place to start.We can also use the DNA as a way to develop tests so that we can understand how diverse whale shark populations are. So far, we think that whale sharks are all one species. But to be kind of frank, I don’t really believe that. 

I believe we probably haven’t looked hard enough at their genes yet.The scientists hope to compare tissue samples collected from the captive animals to those of other areas, to determine whether or not there are distinct sub-populations.That’s a big shark! As we probe further into their genetic sequence,I expect that we’ll find differences between Atlantic whale sharks and Indo-Pacific whale sharks. 

Because it’s very unlikely that whale sharks are going around the bottom of South America, it’s just too cold for them down there.

The oceans are still full of mysteries. Whale sharks may be the biggest fish in the sea, but so far we only know very little about these gentle giants.I love being offshore with the animals, and those days when it’s really hot, and really still, and all you can hear is the swishing of tails and dorsal fins through the water.

And I like to think about the fact that this species has been on the planet for 70 million years. So back in the days when it was dinosaurs, and not tourists that were roaming the Yucatan,whale sharks were already here, they were already probably doing exactly what we’re seeing them do right now. I always come back from the field with renewed energy for science, and renewed energy for trying to understand the biology that’s all around us.

 Anyone who tells you that there isn’t great stuff yet to be discovered in the oceans, hasn’t stuck their head underwater lately, because there’s still plenty of cool stuff to see.

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