Tag Archives: whale shark

Diet check: the whale shark is more “vegetarian” than we thought

The elusive whale shark, the world’s largest fish, seems to endure long periods of starvation and eats more plants than initially thought, a new study concludes.

Image credits: Red Brick.

The ocean is an incredibly large ecosystem, hosting a dazzling array of creatures. You might have some trouble believing that a 12-meter shark weighing over 20 tons roams the seas, scouring the water for… plankton. Indeed, the whale shark I’ve just described is not a fearsome predator, but rather a filter-feeding shark, surviving on krill, fish eggs, crab larvae, and only the occasional small fish or octopus caught in its 1.5 m (4.9 ft) wide mouth.

However, as a new study reports, they might also indulge in plant-eating, much more than previously thought. They also seem to go long periods without eating anything.

Much still remains unknown the behavior and habits of the whale shark (Rhincodon typus) — and following them around is not very practical. So along with his colleagues, Alex Wyatt, a project researcher at the Atmosphere and Ocean Research Institute, carefully monitored the growth, diet, and health of three whale sharks living in an aquarium and two whale sharks living in ocean net cages. They complemented these observations with blood tests and tissue isotope analyses.

“Whale sharks are one of the most exciting organisms to encounter for tourists and scientists alike, not just due to their sheer size, but also their grace and beauty. It is a privilege to unveil some of the mystery surrounding their lives,” said Wyatt.

“Similar to blood tests performed when you visit the doctor, we are able to assess the health of whale sharks based on the contents of their blood,” said Wyatt. “We combine blood tests and tissue isotope analyses to create an accurate health check for the animals.”

Wyatt found that several of the wild whale sharks had gone without eating for weeks or months, according to the blood tests. It’s unclear if they hadn’t found anything to eat or if they just don’t eat during their long migrations when the analyses were taken. Researchers also found evidence of substantial plant consumption, suggesting that the two might be connected.

“This is a somewhat surprising and controversial finding, since whale sharks are generally assumed to feed strictly on higher levels of the food chain. However, some whale sharks have been found with seaweed in their stomachs and eating plants might make sense if feeding opportunities can become as limited as our blood tests suggest,” said Wyatt.

Understanding these sharks is crucial for conservation efforts. Already, the species is classified as endangered by the International Union for the Conservation of Nature, as their numbers and habitat have decreased dramatically, primarily due to human activity like offshore drilling and fishing.

However, Wyatt cautions that his findings might only be representative of some populations of whale sharks in the wild. He plans to carry further, more thorough health checks.

The study has been published in Ecological Monographs.

NASA algorithm and citizen scientists allow biologists to track whale sharks

It’s always exciting when research from one field is applied to another. This time, it’s applying astronomical data and citizen science to whale sharks.

The spots on a whale shark do kind of look like stars in the night sky. Credits: Max Pixel.

It’s always surprising how much NASA’s work affects other fields of science, and ultimately, our lives. It’s not just about space flight or satellites, things like solar cells, highway de-icing and 3D printing all benefitted from NASA’s work. Now, lead scientist Dr. Brad Norman from Murdoch University was able to study whale sharks thanks to an algorithm developed by NASA engineers.

The algorithm was written to analyze star charts, but Norman and collaborators realized they could also use it to detect the white spots on a whale shark. Like fingerprints or stripes on a zebra, these spots are unique for every whale shark. So Norman gathered 30,000 photos of the awe-inspiring creatures from citizen scientists in 54 different countries.

“This effort is helping us to uncover the mysteries of whale sharks and better understand their abundance, geographic range, behaviours, migration patterns and their favourite places on the planet,” Dr. Norman told local newspapers.

“A great example of citizen science where members of the public can play a really positive and active role in monitoring our wildlife, in this case, whale sharks,” he added.

The team identified 20 locations, including Ningaloo Reef, the Maldives, Mozambique and the Red Sea, where the whale sharks gather, predominantly in male-dominated groups (males accounted for up to 90% of the group population). They only knew about 13 of these places before the project started. Meanwhile, in places like the Galapagos, 99 percent of the whale sharks were female. The scientists also identified some of the preferred migration routes of the creatures.

“Citizen science has been vital in amassing large spatial and temporal data sets to elucidate key aspects of whale shark life history and demographics and will continue to provide substantial long-term value,” the paper concludes.

Whale sharks can grow up to 12 meters long (39 feet). They’re gentle giants, slow-moving filter-feeders, the largest known extant fish species. However, despite being so big, they’ve been especially elusive until the 1980s. We don’t really know how many whale sharks there are in the world and as a result, their conservation status is hard to estimate. Researchers believe that this study could help with such estimates and could also help direct conservation efforts to where they are most needed. Engaging the general public is also a great way of increasing awareness and support for such efforts.

Journal Reference: Bradley M. Norman et al. Undersea Constellations: The Global Biology of an Endangered Marine Megavertebrate Further Informed through Citizen ScienceBioSciencehttps://doi.org/10.1093/biosci/bix127.

Borneo orangutan and two shark species hit extinction ‘red list’

It was a sad announcement, as conservationists revealed that three emblematic creatures just entered the extinction red list: the Bornean orangutan, the world’s biggest fish – the whale shark – and a hammerhead shark species.

Photo by Eric Kilby.

“It is alarming to see such emblematic species slide towards extinction,” Jane Smart, head of IUCN’s Global Species Programme, said in a statement.

It’s highly worrying to think that future generations could only see these creatures in zoos and movies, but that’s a clear possibility by now. The Bornean orangutan, which along with its cousin the Sumatran orangutan are Asia’s only great apes, has moved from being classified as “Endangered” to “Critically Endangered” – which means it’s basically just one step away from extinction. To make things even worse, this situation is hardly reversible.

“As orangutans are hunted and pushed out of their habitats, losses to this slow-breeding species are enormous and will be extremely difficult to reverse,” Erik Meijaard, an IUCN assessor of the species said in the statement.

The main problem is habitat loss. As humans continue to expand and create more plantations for palm oil and rubber, they are destroying more and more of the rainforest. Also, for the past four decades, 2,000 to 3,000 of the orangutans have been killed every year by hunters or locals who see them as pests.

IUCN also warned that the slow-moving whale shark, which can measure up to 12.65 metres (41.5 feet) is suffering a similar fate. The shark is being killed because its fins are considered a delicacy in some parts of Asia. It is also accidentally caught by fishing nets aiming for tuna.

An emblematic hammer shark is also threatened. The small brownish grey shark, which has an exceptionally large “hammer” is especially prone to getting trapped in fishing nets due to its shape. It’s difficult to estimate how many of these sharks still survive, but their numbers are definitely dropping.