(Wikimedia/Zac Wolf)

Revealing the mysteries of the magnificent, elusive whale shark

Imagine trying to collect a blood sample from a fish the size of a school bus, with skin like sandpaper four inches


Alistair Dove
September 24, 2017 12:00AM (UTC)
This article was originally published by Scientific American.

Being in the presence of the largest fish in the world is a wonderful feeling. Your eyes can’t help but gaze at its intricate pattern of spots and lines and the way they reflect in a mosaic fashion against the rippling sunshine from the sea surface. There’s a soft sway to its massive caudal fin as it serenely propels the animal forward through the endless blue. I imagine it feels similar for the entourage of tuna, remoras and other hangers-on that seem to admire its underbelly and innocently chase a free ride from its slipstream. Yes, a whale shark is a thing of wonder. But more so, it’s a thing of mystery.

We don’t know much about the whale shark, and what we do know was difficult to uncover. I know, because that’s my job. As a marine biologist, my focus lies in the diversity and health of aquatic animals and their environment, at study sites from the Yucatán peninsula of Mexico and the Galápagos Islands of Ecuador, to the remote South Atlantic island of St. Helena. On our most recent expedition, to Cenderawasih Bay, in Indonesia’s West Papua area of New Guinea, a team of researchers from Georgia Aquarium, Conservation International, Indonesian partners and I have been opening up a new frontier in this quest for whale shark knowledge.

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Gathering useful research data about this elusive and mysterious species is difficult for many of the same reasons that make it so spectacular: size, speed and a habitat that spans two thirds of the globe. Sure, you can observe the grandeur of its external characteristics; a juvenile male whale shark can be up to eight meters in length. We can track their movements across the globe using satellite tags to better understand their migratory patterns, and we can count the number of whale sharks to make estimates about the health of a population’s numbers. But simply counting animals as a measure of health is a blunt and imperfect instrument.  What we really want is to understand what happens inside the animals.

Gaining access to valuable health data is a logistically complex and physically grueling endeavor, and to this point has proven a nearly impossible feat. Imagine trying to collect a blood sample from a fish the size of a school bus with skin like sandpaper that’s four inches thick and a mouth wide enough for a human to comfortably nap inside of. The massive fish move at a pace that only an Olympic swimmer could keep up with for any length of time. Trying to swim at that pace, burdened with scuba gear, while gathering measurements, assessing body condition and attempting to gather a blood sample is like struggling to knit while riding a bicycle. As a result, nearly everything we know about this incredible species has been gathered during very brief 30- to 60-second encounters that really limit what you can do — until now.

With the help of Indonesian fishers and their government, and a unique partnership between a public aquarium and a conservation NGO, a whole world of data from wild whale sharks is now at our fingertips thanks to an unusual interaction between whale sharks and a type of traditional Indonesian fishery in Cenderawasih Bay.

Formally called a bagan fishery, this square-framed lift net has been used by Indonesian fishers for decades. They target schools of baitfish by lowering large nets beneath specialized floating wood or bamboo platforms and use bright lights at night to attract the baitfish above the nets—which are then quickly lifted to catch the entire school at once. This “free” meal is too good to pass up for whale sharks, which can be seen feeding on the baitfish around the bagans all year round. In the process, the whale sharks can accidentally trap themselves in the nets. Fishers, who regard whale sharks as a sign of good fortune, release them after clearing the nets of their catch. Working with the fishers during the day, we can also target specific animals, enticing them into the net with scoops of baitfish.

These whale shark catches provide just enough time with the animal sitting still to conduct comprehensive medical examinations including drawing blood samples for the first time ever, taking measurements and attaching satellite tracking tags. It’s a low-stress interaction for both the animals and the biologists.  Whale sharks differ from many shark species in that they do not need to swim forwards in order to breathe, and they seem perfectly happy to wait quietly in the bagan until they are released, when they usually circle right back around and start feeding again!

When a blood sample is collected from a whale shark, which can be from any of 5 different places on the body, it is brought to a nearby makeshift lab on the research boat to begin testing. We are looking for several things: properties of blood gases, blood cells, and blood chemistry, including indications of infectious disease or pollution exposure. What we find tells us not just about the internal health of the whale shark, but the health of the waters it so gracefully resides in and how that can be impacted by human activity.

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One of the research questions I’ve been eager to address is what effect, if any, does plastic pollution have on these filter feeders that skim the water’s surface to collect their meals, exactly where tiny particles of marine plastic also accumulate. Because rapid development has outstripped waste management infrastructure, Indonesia is one of the top five plastic polluting countries in the world (the other four are also in Southeast Asia), so it’s an ideal place to conduct this kind of study.

Measuring the effects of pollution scientifically can help organizations like Conservation International coordinate their outreach programs in places where endangered animals like whale sharks are found, helping governments and empowering local communities to reduce damaging pollution. Back at Georgia Aquarium, in Atlanta, we can use this information to inform discussions with guests and with companies in the United States that may be manufacturers of some of the plastics that are turning up in our oceans. These might seem like disparate entities, but supply chains are increasingly globally connected, and the ocean is too, so it will take collaboration and cooperation on a global scale to work toward a healthier and more sustainable ocean.

While the human population of West Papua is diverse, many Indonesians, notably the fishers, revere the whale shark as a sign of good luck. I’d say I agree. Lucky is exactly how I feel every day about working with these animals whether it’s in Southeast Asia or at the Georgia Aquarium, the only institution in the Western Hemisphere that provides care for these incredible creatures. It’s a privilege to be learning new things about them all the time and sharing those findings with members of the public who visit the aquarium and are unlikely to see a whale shark anywhere else in their lives.

While slowly uncovering the mysteries of the whale shark, we are beginning to piece together a puzzle of both this endangered species and the broader health of our one globally connected ocean, which is the dominant geographic feature of our planet.

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Alistair Dove

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Related Topics ------------------------------------------

Biology Marine Biology Marine Life Scientific American Sharks

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