The Whale Sharks of Isla Mujeres… Every year, as the summer heat descends on the Yucatan peninsula. A truly amazing phenomenon happens to the north-east of the small holiday island of Isla Mujeres.
Local fishermen call it the “Afuera’’ – Mexican for outside. In reference to those deeper waters offshore from the tip of the Yucatan. Where, come July and August, the largest known gathering of whale sharks (Rhincodon typus) takes place.
Long considered as solitary giants roaming the open oceans, aggregations seemed quite rare. And, prior to the discovery of the Afuera, a large gathering was thought to be 15 to 20 whale sharks. Typically those aggregations were associated with high seasonal concentrations of zooplankton.
But it seems that whale sharks are really quite social creatures when something special is on the menu. And the Afuera offers them something really different… An almost unlimited quantity of rich, energy-dense nourishment. With literally hundreds of whale sharks gathering to gorge themselves on this “all you can eat” buffet of nature.
The Afuera… Hidden in Plain Site
Incredibly it would seem that this massive aggregation has been happening for many years, generations possibly… All quite unbeknownst to either the scientific or ecotourism communities. But the local fishermen knew, and the first rumors apparently surfaced as early as 2002.
However, at that time all the attention was on a different aggregation. The recently discovered gathering of whale sharks and manta rays in the shallow coastal waters of the northern tip of the Yucatan. Between Cabo Catoche and Isla Holbox,
The discovery of the “Cabo Catoche aggregation” led to a number of scientific surveys to quantify the population and dynamics.
Followed by the eventual establishment of a Whale Shark Biosphere Reserve by the Mexican government in 2009.
It also created a thriving and regulated ecotourism whale shark watching industry on nearby Isla Holbox.
So, it was not until September 2006 that the Afuera was actually investigated. When Mexican whale shark scientist Rafael de la Parra managed to organize a series of five aerial surveys.
Flight Paths of the Aerial Surveys in September 2006 – Courtesy of Rafael de la Parra
What the survey revealed astonished everyone involved. Because not only were the rumours true, but the numbers of whale sharks spotted were almost unbelievable. With a total of 480 sightings recorded in an elliptical area of open ocean of about 18 km2!
The Whale Sharks of Isla Mujeres – Timing…
The Cabo Catoche aggregation happens in the shallow coastal waters off the north-eastern tip of the Yucatan peninsula. Beginning in May and ending around in mid-September. With the most whale sharks present for a few weeks from late July to the middle of August.
They gather to feed on the seasonal spawning of crustaceans (copepods and sergestid shrimp). And the aggregation is known for the its turbid waters and poor visibility. Which makes any kind of underwater photography quite challenging.
And yet at the Afuera, just 55-65 kms away, huge numbers of whale sharks were gathering. In what, from the air, appeared to be deep and clear blue water…
The Whale Sharks of Isla Mujeres – Little Tunny
Subsequent investigations by de la Parra revealed the presence of huge quantities of fish eggs in the water. Which DNA testing identified as from the little tunny (Euthynnus alletteratus), the most common tuna in the Atlantic Ocean.
Little tunny can grow to about 900mm in length and weigh up to 12kg. But the average size is just over half of that. A fraction of the larger species of tuna and most probably how it got its name!
But what little tunny lack in overall size they make up with their prolific ability to breed.
Which they do by the females releasing massive quantities of eggs into the water column. Followed by the males releasing their sperm.
The female little tunny are incredibly fertile creatures. And are able to release around 1.75 million eggs over the course of a mating season. Those eggs are circular and transparent. Plus they are buoyant because they contain a droplet of oil. So they are pelagic and able to float in the current.
In the Atlantic Ocean those mating seasons happen from around the middle of April. When the water temperature reaches about 25°C (77°F) and can last until mid- September. With the most intense spawning occurring in July and August.
The main spawning areas are in offshore waters that are typically 30m to 40m deep. All of which perfectly describes the location and timing of the Afuera!
The Whale Sharks of Isla Mujeres – Whale Shark Tourism
Just as a significant whale shark watching industry has been established around the Cabo Catoche aggregation from Isla Holbox. A similar but bigger one has grown around the Afuera… Serviced from both Cancun and nearby Isla Mujeres.
Isla Mujeres from the Air… With Cancun in the Distance
The big difference between the two is that Cabo Catoche occurs within the Whale Shark Biosphere Reserve. And so it is regulated… But, unfortunately for now at least, the Afuera is neither protected or regulated.
There is a lot you could say about both Cancun and Isla Mujeres – both positive and negative… And I can only offer my personal opinion, which is that Cancun is simply not my cup of tea. I found it far too touristy and over-developed. While Isla Mujeres has a much more laidback and slightly rustic charm plus the principal form of transport are golf carts!
The estimated 2m tourists who visit Cancun every year have a wide array of entertainment options available to them. And in the Afuera season that includes “guaranteed” whale shark swimming.
A similar mechanism occurs on Isla Mujeres and what that means is every morning a veritable armada of whale shark swimming boats leave from both locations. The “guaranteed” part means that the tourists will be in the water with the whale sharks twice. Basically they will get their turn as the people on board each get immersed…
It is hardly a quality experience, but in all probability, is all most of the tourists want. And what appears to happen is that the operators bring the tourists out, give them two immersions with the whale sharks and then it’s time to get back to Cancun or Isla Mujeres!
The Whale Sharks of Isla Mujeres – Quality Time…
To have any kind of quality time with the whale sharks you need to sign up for a private tour. Which means that somebody organizes all the logistics for you, so you can turn up with your camera, mask and fins to enjoy the experience.
That is exactly what I did and was pleased with the overall outcome which involved five full days out on the water. Being in a private boat has a lot of advantages. And means that you stand a good chance of getting to the whale sharks before the tourist armada arrives. So you can have some good encounters before it all turns into a zoo…
Then it’s a question of finding a good spot to continue swimming with the whale sharks. But be ready to be surrounded by a bunch of tourists dropped in beside you!
But the zoo part does not last that long… As the boats want to get back as soon as they have fulfilled their two-encounter guarantee. Typically, that is about two hours or so. And then the number of boats starts to decline rapidly and calm returns.
Interestingly, none of this seems to bother the whale sharks. They just get on with what they are there for – feasting on the little tunny eggs.
The Whale Sharks of Isla Mujeres – In the Water
Personally, prior to my trip to Isla Mujeres, I had very limited experience of in-water encounters with whale sharks. Those that I had had, in places like Mozambique, Papua New Guinea and Socorro in Mexico, are probably best described as fleeting…
On the surface encounters in Mozambique revolved around cruising whale sharks looking for food. And the best chance of a quality encounter was if a shark found a large quantity of floating plankton. In which case it would hang around till it was all consumed.
Otherwise it was basically a “drive-by” where you are dropped in front of an approaching whale shark and they swim towards and past you. There is very little chance of staying with a whale shark when it is swimming as they move decidedly quicker that they look like they are…
Whale Shark “Banking” in Mozambique
Often though, the whale shark would see you and the other snorkellers and then resort to “banking”. A defensive mechanism whereby they dive down and turn their back, with its really thick hide, on you.
Underwater on scuba in PNG and Socorro the encounters are even more fleeting. As it is more of a three-dimensional meeting that the two-dimensional ones at the surface. The time spent with the animals seems like milliseconds as they quickly move on!
But at Isla Mujeres the whale sharks are so focused on feeding that they basically ignore you. Which means you can have some very close encounters! The buoyant little tunny eggs keep the whale sharks at the surface, and they are simply feeding to their heart’s content.
You and all the tourists seem to be nothing more that a minor annoyance. One that is quickly forgotten as they continue to feed!
The Whale Sharks of Isla Mujeres – Migration Patterns
Whale sharks and their migratory patterns are a source of great mystery… And nobody really knows where they come and go. However, from a very layman-like and non-technical perspective, it would seem that they have a routine that they follow, with key way-points where they can feed as they grow.
For example, at Tofo in Mozambique the whale sharks that gather there are a certain size. As are the ones at Isla Mujeres and Cabo Catoche. While in the Galapagos some really big ones are seen in the season.
Well-known whale shark scientist Simon Pierce made a back of the envelope calculation that while at the Afuera, the animals consume about 143kg of little tunny eggs during an 11 hour feeding period.
Which seems an awful lot. But it needs to taken into the overall context that they are gorging while they can. And long periods can follow where the whale sharks may not find food at all!
It also explains why it is believed that many of the whale sharks tagged and identified at both Cabo Catoche and the Afuera stay in the overall area for up to six months at a time. Plus, why you and the tourists are ignored… these guys are focused on the food!
The Whale Sharks of Isla Mujeres – Feeding Time…
Knowing that basic fact allows their in-water behavior also to be understood. Something that took me a couple of days to rationalize when I was there in the thick of it all.
Think of the whale sharks as totally focused on the food supply. And while they are swimming forward at the surface, they can ingest what is immediately in front of them. For a whale shark, that is a good thing… As they might go for considerable periods where there is no food in front of them!
So, when they eventually swim out of the area where the tunny eggs are, they stop. And, it would seem they simply turn around and go back.
What that means for you is that if you have been dropped in where the tunny eggs are, there will be an endless procession of whale sharks making their way backwards and forwards through their personal little tunny egg corridor.
And all you have to do is stay where you are and look for the next one. Practically, that means that as soon as you have finished one encounter you need to be looking for the next approaching whale shark. So, you need to try and fin up a bit and spot the next approaching fin and get in position.
The Whale Sharks of Isla Mujeres – Bottle Feeding
For me the most spectacular encounter possible during the Afuera is the “Botello” or bottle feeding. This appears to happen when the whale shark happens upon a large patch of food. That can be little tunny eggs at the Afuera, crustaceans at Cabo Catoche or just plain old zooplankton elsewhere.
The whale sharks seem absolutely determined to consume every piece of that patch of food. And to make sure they do, they assume a vertical position and basically hoover up every last piece. As they do that they seem totally fixated on the task at hand, which allows you to have a great and really close encounter.
Although it has to be said that the size of a whale shark’s mouth does create thoughts about Jonah and the whale when you get really close!
The Whale Sharks of Isla Mujeres – In Conclusion
The annual Afuera aggregation is a must-do if you are into seeing and photographing “big animals”. Whale sharks are after all the biggest fish in the sea and the encounters with them to the north of Isla Mujures are very special.
Simply stated, being in the water with so many whale sharks, where all you have to really do is wait for the next one to appear simply, does not happen anywhere else – at this point in time at least…
It is so special and clearly of profound importance to whale sharks in general, we have to hope that Rafael de la Parra and his wife Beatriz, together with people like Simon Pierce can convince the Mexican government to extend the current biosphere at Cabo Catoche to cover the Afuera!
The Whale Sharks of Isla Mujeres – X-Ray Article
The full version of the whale sharks of Isla Mujeres was also published as an 8-page article in the global diving magazine X-Ray.
You can use the following link to download the full Whales Sharks of Isla Mujeres article.