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© Ethan Daniels / Shutterstock
© Ethan Daniels / Shutterstock

Five Incredible Whale Shark Discoveries of the Last Decade

Added to Blogs on 27 August 2020
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Let’s celebrate this year's Whale Shark Day by learning about five fascinating facts scientists have discovered about these gentle giants in the past decade, from having a unique eye armour to figuring out how old they are by studying atomic bomb tests!

Whale sharks have a special armour protecting their eyes

2 Large WW2122237A whale shark near Isla Mujeres, Quintana Roo, Mexico © WWF / Vincent Kneefel 

The fact that shark skin is covered with tiny teeth – denticles – has been known for a long time. But did you know that whale shark eyes are covered with hundreds of tiny teeth as well? As a team of Japanese scientists discovered, a unique “armour” made up of as many as 2,900 tiny denticles covers each eye of this fascinating creature. These special denticles differ in structure and build from denticles found on their skin and that is because the eye denticles fulfil a different function. Since whale shark eyes protrude on each side of the animal’s head, no wonder they need this special armour for mechanical protection. So far it also seems no other shark species has this special feature, making whale sharks even more unique!

Whale shark age can be estimated correctly because of Cold War nuclear explosions

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A whale shark with a school of barracuda in Tubbataha, Philippines © Simon Lorenz / WWF-HK 

Understanding how species grows, matures, and ages is crucial to being able to protect it effectively. Previously, scientists used to count growth bands in whale shark’s vertebrae to determine the animal’s age, which works just like counting tree rings. However, the researchers around the world could not agree whether these bands were developing in whale sharks once a year or every two years, which makes a massive difference. Earlier this year scientists were able to finally solve this puzzle because of the atomic bomb tests that took place in the 1950s and 1960s. These explosions doubled the amount of a particular carbon isotope (Carbon-14) in the atmosphere, which was eventually absorbed by all living organisms on the planet. As we know how fast this carbon isotope decays over time, it can be used to determine age. Using this particular method for the first time, the scientists were finally able to confirm that vertebral bands do form in whale sharks each year. This means we are finally able to estimate the age of these giants correctly, with the oldest specimen recorded to be 50 years old.

Whale shark mommas act as giant sperm banks

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A whale shark in Donsol, Philippines © naturepl.com / David Fleetham / WWF

While a lot remains to be discovered about the reproductive cycle of these giants – and especially where they give birth – one important discovery was made 10 years ago when a team of scientists studied whale shark embryos found inside a large female caught off the coast of Taiwan 25 years ago. 304 embryos in different development stages were found at the time, far exceeding the highest number recorded for any other shark species. But how it was possible for the babies to be of different sizes and development stages was just speculation back then. Scientists thought that perhaps the pups were fathered by different males at different times, which would explain the differences in development. However, it wasn’t until recently that researchers were able to confirm that all those baby whale sharks had the same father thanks to paternity DNA tests. Most of all, this discovery revealed that female whale sharks can act as gigantic sperm banks, able to store sperm and fertilise eggs over a period of time. As scientists explained, whale shark mommas do that to maximise the chances of survival of her babies.   

Whale sharks in Indonesia eat up to 137 pieces of plastic per hour

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A whale shark swims near a floating plastic bag in Oslob, Cebu, Philippines © Steve De Neef / National Geographic Creative

As whale sharks filter-feed at the surface and several dead individuals have been found with significant amounts of plastic in their stomachs, scientists have long speculated that marine plastic pollution must be impacting these giant fishes. We just did not understand how serious things really were. A team of scientists recently studied the impact of marine plastic pollution on whale sharks in Indonesia and sadly, what they found out was not good news. Located in the heart of the Coral Triangle, Indonesia was selected for this study as it takes the infamous second place on the list of world’s largest marine plastics polluters. After studying plastic abundance in 3 locations around the country, the researchers concluded that whale sharks could be eating up to 137 pieces of marine plastic per hour! And this includes both tiny microplastics as well as bigger pieces measuring nearly 50 cm! Although whale sharks do have the ability to “cough” out large objects that accidentally end up in their mouths, judging from necropsies of individuals found on beaches around the world, that mechanism does not always work. As one report from Sabah in Malaysia revealed, a plastic bag measuring 46 cm by 32 cm killed one whale shark there. Who could think that something so small could lead to the death of one of the biggest animals on the planet? So next time you buy groceries or get that take-away dinner, remember to avoid single-use plastics and instead opt for more sustainable and eco-friendly alternatives. And if you have a moment to spare, please sign and share this petition to help stop plastic pollution if you haven't done that already.

Whale shark teenagers are real homebodies

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Whale shark swimming in crystal clear waters in Thailand © 22August / Shutterstock

Although we know that whale sharks can migrate large distances (e.g. one tagged female named Anne travelled over 20,000 km in 2 years and 3 months!), thanks to several different teams of scientists studying their regional aggregation sites all over the world, we now know that young males are actually real homebodies. Recent studies revealed that they hang around the same areas over long periods of time, often returning to same spots year after year. Some sharks studied in the Western Atlantic Ocean were spotted there for over 10 years and others in the Indian Ocean returned to the same site for 7 consecutive years! These discoveries were possible because individual whale sharks can be identified – and therefore tracked – thanks to their unique skin patterns. A constellation of white dots covering their bodies act in the same way for whale sharks as fingerprints do for us, people. Interestingly enough, animals found at these aggregation sites were mostly juvenile males – with females and adult males spotted rarely. Even though we are talking here about the biggest fish – which, it seems, should be easy to track and find – we still do not know where females and adult males spend most of their lives. We also still don’t know where whale sharks give birth and spend their first years of life… All these mighty secrets are still waiting to be uncovered!

Big troubles versus the big fish

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An archival photo from 2001 from a whale shark fishery. Whale sharks used to be targeted for meat and fins in various places around the world. © Jürgen Freund / WWF 

Even though whale sharks could seem invincible due to their impressive size (after all, large adults can weigh even as much as six large African elephants!), the reality is very different. Whale sharks are endangered and at risk of disappearing from our blue planet forever.

One of the main threats pushing them to the brink is fishing, although these days whale sharks are mostly caught by accident (as bycatch). Whale sharks can easily get tangled in fishing nets and in those places where they frequent the same areas as schools of tuna, some fishers may even set nets around these gentle giants on purpose to maximise their chances of catching more tuna. Being highly migratory animals and filter-feeding at the surface, they are also at risk of ship strikes, especially when their feeding areas collide with shipping lanes. Irresponsible whale shark tourism – where animals are harassed, there are too many tourists and boats, or regular food provisioning is changing sharks’ natural behaviours – can also pose a threat to whale sharks.

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A snorkeler photographs a whale shark near Isla Mujeres in Mexico © naturepl.com / Alex Mustard / WWF 

Luckily, not all is lost! If we act now and implement conservation solutions based on science, we can still save these gentle giants for future generations and let them roam our deep blue oceans till the end of time! Here are five things that need to happen to save these oceanic nomads:

  1. identify where shipping lanes cross whale shark migration routes;
  2. reduce their chances of getting caught by fishing operations;
  3. conserve their key habitats such as aggregation sites;
  4. ensure whale shark tourism is done responsibly and sustainably;
  5. and work together across borders to keep them safe as they cross entire ocean basins.

Check out the stories below to find out more about what WWF is doing to protect these fascinating animals from Mexico, to Philippines, to Pakistan, and Tanzania. And don't forget to click here to learn more about how you can help.

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References

Andrzejaczek, S., Meeuwig, J., Rowat, D., Pierce, S., Davies, T., Fisher, R., & Meekan, M. (2016). The ecological connectivity of whale shark aggregations in the Indian Ocean: a photo-identification approach. R. Soc. open sci. 3160455 https://doi.org/10.1098/rsos.160455

Germanov ES, Marshall AD, Hendrawan IG, Admiraal R, Rohner CA, Argeswara J, Wulandari R, Himawan MR and Loneragan NR (2019) Microplastics on the Menu: Plastics Pollute Indonesian Manta Ray and Whale Shark Feeding Grounds. Front. Mar. Sci. 6:679. https://doi.org/10.3389/fmars.2019.00679 

Guzman, H. M., Gomez, C. G., Hearn, A. & Eckert, S. A. (2018). Longest recorded trans-Pacific migration of a whale shark (Rhincodon typus). Marine Biodiversity Records, 11(8). https://doi.org/10.1186/s41200-018-0143-4

McKinney, J. A., Hoffmayer, E. R., Holmberg, J., Graham, R. T., Driggers, W. B., 3rd, de la Parra-Venegas, R., Galván-Pastoriza, B. E., Fox, S., Pierce, S. J., & Dove, A. (2017). Long-term assessment of whale shark population demography and connectivity using photo-identification in the Western Atlantic Ocean. PloS one, 12(8), e0180495. https://doi.org/10.1371/journal.pone.0180495

Ong, J. J. L., Meekan, M. G., Hsu, H. H., Fanning, L. P. & Campana, S. E. (2020) Annual Bands in Vertebrae Validated by Bomb Radiocarbon Assays Provide Estimates of Age and Growth of Whale Sharks. Frontiers in Marine Science. https://doi.org/10.3389/fmars.2020.00188

Rohner, C.A., Cochran, J.E.M., Cagua, E.F., Prebble, C.E.M., Venables, S.K., Berumen, M.L., Kuguru, B.L., Rubens, J., Brunnschweiler, J.M., & Pierce, S.J. (2020). No Place Like Home? High Residency and Predictable Seasonal Movement of Whale Sharks Off Tanzania. Front. Mar. Sci. https://doi.org/10.3389/fmars.2020.00423

Schmidt JV, Chen CC, Sheikh SI, Meekan MG, Norman BM, Joung SJ (2010) Paternity analysis in a litter of whale shark embryos. Endang Species Res 12:117-124. https://doi.org/10.3354/esr00300 

Tomita, T., Murakumo, K., Komoto, S. Dove, A., Kino, M., Miyamoto, K. & Toda, M. (2020). Armored eyes of the whale shark. PLoS ONE 15(6): e0235342. https://doi.org/10.1371/journal.pone.0235342

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Author

Magda Nieduzak

Senior Communications Officer, Sharks: Restoring the Balance, WWF-Hong Kong

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