Record Breaking Study Tracks Whale Sharks
Needless to say, the team at Ningaloo Whale Shark Tours n Dive are passionate about the whale sharks that we and our guests encounter on a regular basis. These elusive creatures are masters of migration. Given their enormous size, they must consume a great deal of their favourite food – plankton – on a regular basis. And from March to September, these majestic fish visit the waters of Ningaloo Reef for an extended feast.
But whale sharks are always on the move. Their enormous bodies – which can grow up to 18 metres long and weigh upwards of four to five tonnes – require a great deal of food to eat. The fact that whale sharks feed exclusively on plankton, which are extremely tiny organisms, means that they have to store up reserves when food is available.
The gentle whale shark occasionally eats very small fish or eggs as well, but it wouldn’t dream of eating anything bigger. In fact, its specialised mouth is completely ill-equipped to dine on anything else. But as you can imagine, whale sharks have voracious appetites. They go through an enormous amount of plankton in a daily feeding.
Researchers Focused Their Study at the Yucatan Peninsula
Catering to this insatiable appetite means that whale sharks have to travel epic distances in the course of a year in order to stay full. An ambitious nine-year study on their migration habits was recently completed, and the results are fascinating. This was the largest study of whale shark migration ever undertaken, and it has helped researchers solve the age-old mystery of where whale sharks give birth.
Whale sharks are known to congregate at a few feeding locations around the world. In addition to Western Australia, they also travel to Indonesia and Belize. And from May to September, a large group arrives off the coast of Mexico, northeast of the Yucatan Peninsula. Researchers have counted upwards of 800 of these gentle giants feeding here at this time, and this is where the study was focused.
Study co-author Robert Hueter (who is also the director for the Centre for Shark Research at Mote Marine Laboratory, explained to National Geographic why this location was of particular interest to researchers:
“From this one feeding area, these animals spread out over vast parts of the region—throughout the Gulf of Mexico, down into the Caribbean Sea, through the Straits of Florida up into the open Atlantic Ocean. We found animals coming back for as many as six years at a time. Clearly they are returning to this site to fuel up on the rich food that’s there to carry them through much of the rest of the year.”
The fact that so many whale sharks come here on a regular basis gave Hueter the idea to launch this study back in 2003. We’ll look at the details of what he discovered in the next section.
Results of the New Whale Shark Study
Hueter and his team began by tagging as many whale sharks as they could and monitoring their migration activity via satellite. This allowed them to watch migratory groups of these fish over extended periods of time, revealing a great deal of information about their migratory habits in the process.
The amount of time invested in this study is unprecedented. In the past, researchers have learned most of what they know about whale sharks specifically from the time they spend feeding at places like the Yucatan or around Ningaloo Reef. The same places that are ideal for swimming with whale sharks are also perfect for collecting data. The problem, however, is that this only offers a partial glimpse into the lives of whale sharks. Where do they go and what do they do when they are not actively storing up during the peak feeding season?
Previously, scientists weren’t able to confidently answer these questions. Before these tagging efforts were underway, researchers had to acknowledge that they only knew where the whale sharks were for about six months out of the year. The fact that whale sharks can seemingly vanish for months at a time is impressive, considering their sheer size.
Of the 800 whale sharks that were involved in this study, a particular female stood out. She was presumably pregnant and embarked on an incredible journey that spanned 7,800 km of open sea. She swam out into the waters between Brazil and Africa, and as she was crossing the Equator, her tag came off. Read on to find out why this particular journey is so important to researchers.
Where Are All the Female Whale Sharks?
When you swim with whale sharks, it’s relatively easy to differentiate the males from the females once you know what to look for. The males have large extensions (which are called claspers) on their pelvic fins, and the females do not. And if you have a quick look around, you’ll notice something unusual – there are far more males than females in the group.
It’s extremely unusual for this sort of gender imbalance to exist in animal populations. For that reason, scientists have long suspected that there are more females out there that they simply aren’t seeing. When this particular female disappeared in equatorial waters, they believe they may have found the answer to a persistent question.
Based on the tagging data, the researchers now think that the pregnant females may be heading deep into the middle of the ocean to give birth around remote islands or seamounts. This makes sense, given the fact that baby whale sharks are quite small and potentially vulnerable to predators. Giving them time to grow and develop at a remote location could increase their chances of survival.
This hypothesis would help to explain why it’s relatively rare to see new-born or very young whale sharks in popular feeding areas like Ningaloo Reef. They’re most likely being cared for at a remote nursery site.
If you’re spending time in Western Australia and would like to see these amazing creatures up close and in their natural habitat, get in touch with us to arrange a Ningaloo whale shark swim. It truly is a once-in-a-lifetime opportunity!